Input, Innateness, and Induction in Language Acquisition JAMES L. MORGAN Department of Cognitive and Linguistic Sciences Brown University Providence, Rhode Island
Input and innateness compliment one another in language acquisition. Children exposed to different languages acquire different languages. Children’s language experience, however, underdetermines the grammars that they acquire; the constraints that are not supplied by input must be available endogenously, and the ultimate origin of these endogenous contributions to acquisition may be traced to the biology of the mind. To the extent that assumptions of innateness encourage greater explicitness in the formulation of theories of acquisition, they should be welcomed. Excessively powerful assumptions of innateness may not be subject to empirical disconfirmation, however. Therefore, attention should be devoted to the development of a theory of language input, particularly with regard to identifying invariants of input. In combination with a linguistic theory providing an account of the endstate of acquisition, a theory of input would permit the deduction of properties of the mind that underlie the acquisition of language.
Language is the product of the child’s attending to, representing, and analyzing linguistically relevant input in a fashion sanctioned by imperatives of human nature. This interactional position is acceded to by virtually all theorists, including strong nativists such as Chomsky, who, in outlining the goals of the study of language, has written: We must determine how the child comes to master the rules and principles that constitute the mature system of knowledge of language. The problem is an empirical one. In principle, the source of such knowledge might lie in the child’s environment or in the biologically determined resources of the mindlbrain, specifically, that component of the mind/brain that we might call the language faculty; interaction of these factors provides the system of knowledge that is put to use in speaking and understanding. (1988, p. 15)
In this article, I advocate an intermediate position on the question of innateness in language acquisition. Several arguments lead irresistibly to the conclusion that Reprint requests should be sent to Dr. James L. Morgan, Department of Cognitive and Linguistic Sciences, Brown University, Box 1978, Providence, Rhode Island 02912. Received for publication 1 September 1988 Revised for publication 30 August 1989 Accepted at Wiley 13 July 1990 Deuelopmentnl Psychobiology 23(7):661-678 (1990) 0 1990 by John Wiley & Sons, Inc.
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acquisition could not proceed without preprogramming. If the descriptions provided by present-day linguistic theories come anywhere close to being psychologically valid (these theories at any rate provide insightful and wide-ranging accounts of the truly formidable intricacies of natural language), then the extent of required preprogramming may be substantial indeed. Nevertheless, admitting innateness into the explanatory armamentorium does not exclude learning: language is not innate OY learned; language is innate and learned. On this view, the key theoretical issue is how to apportion explanatory responsibility between input and innateness. At present, this decision is largely uninformed by empirical findings. I argue, however, that strong assumptions about input should be favored in principle. My argument hinges on differences in vulnerability to disproof between assumptions of input and innateness. Strong assumptions of innateness may not be subject to empirical disconfirmation by the very acquisitional data that they purport to predict and explain. In contrast, it is easy to identify the sort of acquisitional data that would require strong assumptions about input to be abandoned. In the following, I develop these arguments concerning input, innateness, and induction in language acquisition.
Why Language Is in Part Learned The reason why language must be learned is obvious. There are very many different languages in existence, and (with some interesting exceptions including creolization and other instances of generational change) every child systematically succeeds in acquiring the very language (or languages) to which he or she is exposed, regardless of whether this might be the child’s genetically ancestral language. Insofar as any language is a system that relates sounds (or gestures) to meaning, critical components of such exposure-language input-must include hearing (or seeing) examples of the language and having access to the context, physical and social, in which these examples are used, so that their meanings may be educed. The child’s task, then, is to represent and analyze this input, learning which sounds are possible, how sounds may combine with one another to form morphemes or words, what morphemes mean, how words may be combined to form phrases and sentences, what social factors govern appropriateness of particular expressions, and so forth.
Why Language Is in Part Innate-a
General Argument
The reasons why language must be innate are perhaps more subtle, but they are no less compelling. The debate on innateness in language has been muddied somewhat by confusion over both what might be supposed to be innate about language and what is meant by the term “innate.” As Oyama (in press) has noted, “innate” has a history of being used rather loosely as a rubric for several overlapping claims about the origin and nature of behavior. These include having evolutionary history, being species typical, having a genetic basis, being adaptive, being present from birth, arising without relevant experience, occurring independently of the environment, and having a rigid or stereotyped form. Virtually all of these have been advanced by one side or another in the debate over the innateness
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of language. The appropriateness of any particular definition, however, depends upon the precise nature of what is claimed to be innate in language. Claims about innate aspects of language have been made at several different levels of analysis, varying in abstractness. Most concretely, the forms or functions of particular linguistic expressions could be innate. Alternatively, specific aspects of the linguistic knowledge underlying linguistic expressions-one’s grammar-could be innately determined. Most abstractly, the particular learning capacities through which linguistic knowledge is acquired could be innate. I will discuss each of these in turn. The notion that particular overt aspects of language might be innate has a long tradition; here, the sense of “innate” as behavior displaying “rigid or stereotyped form” seems to be most germane. This notion is implicit at several points in Genesis, from the Garden of Eden (Adam’s naming of animals) to the Tower of Babel. Feldman, Goldin-Meadow, and Gleitman (1978) recount a tale from Herodotus in which two monarchs agreed to decide a dispute concerning the primacy of their kingdoms by having two children raised in strict isolation. The dispute was resolved when the children uttered some words in the language of one of the kingdoms, which was thereupon conceded to be the more ancient. King James I is reputed to have conducted a similar experiment, the subject of which supposedly acquired Hebrew. Despite these colorful tales, however, no serious evidence exists to support the view that specific manifestations of language are innately determined. In the literature on feral and isolated children, there is only one example of a child who exhibited any speech upon discovery; further investigation has suggested that this particular child (allegedly the bastard son of a Prussian monarch) was actually held in captivity for several years and trained to utter two or three sentences (Lane, 1976). Others subjected to the cruel natural experiment of social isolation have failed to invent language spontaneously (see Curtiss, 1977, for an account of the modern-day case of Genie). The view that certain aspects of grammar, including rules, relations, and categories of language, might be innate has several modern advocates (see especially McNeill, 1966). Here, “innate” in the sense of “species typical” (or “language universal”) is most relevant. Certainly, some grammatical elements do appear to be universal: languages have a basic unit, the clause, that is used to express propositions-propositions are composed of a predicate and one or more arguments. Distinct classes of words are canonically used to denote predicates and arguments; and one clause may be embedded within another. Investigations of children who are linguistically, but not socially, isolated-deaf children of nonsigning parents-suggest that some of these elements may develop in the absence of relevant linguistic input (for details see Goldin-Meadow, 1982, and Goldin-Meadow & Mylander, 1984). The inventory of universal elements of grammar, however, may be quite limited. Maratsos (1986) argues that the category noun is unique in manifesting common cross-linguistic characteristics; the remaining categories that are usually taken to be most basic, verb, adjective, and preposition, are grouped in virtually all possible combinations in form classes of specific languages. In addition, whereas Chomsky (1986) has argued that there is a universal structural definition of the primary relational category subject, whose acquisition by children is guided by innate principles, Maratsos (1986) has argued that subject lacks any cross-linguistic core of features that would enable its structural properties
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to be discovered. For present purposes, suffice it to say that whether the specific rules, relations, and categories of any given language are innate is a matter of considerable debate. The most unassailable case for innateness, to my mind, may be made at the third and most abstract level of analysis, with respect to the capacities for representing and analyzing input that underlie children’s acquisition of grammars. Here, the sense of “innate” as “arising without relevant experience” is most apt.’ Several considerations argue for the need for constraints on learning in acquisition beyond those that might be supplied by children’s language input. Foremost among these is the logical problem of induction-namely, that for any child, the available input necessarily underdetermines the grammatical system that is acquired (see Goodman, 1983, for a more general discussion of this logical problem). Knowing a language entails being able to produce and comprehend an unlimited number of sentences; yet each child’s linguistically relevant experience is finite. The child must arrive at some sort of general grammatical system based on this finite experience. The logical problem of induction, however, is that there are infinitely many general patterns compatible with any finite range of data, and, hence, the data do not determine the choice of any particular generalization. With respect to language, there are infinitely many (logically possible) grammars compatible with any finite exposure to language, but no such exposure forces the choice of any particular grammar. Nevertheless, individuals who share knowledge of a particular language are able to produce or comprehend more or less the same range of sentences and therefore have arrived at more or less the same generalizations about (or have acquired more or less the same grammar of) that language. (Readers who would dispute this assertion should note that they were able to comprehend the previous sentence, even though it was undoubtedly novel to them. This would not be possible unless they shared with me notions of what constitutes English.) No two children share precisely the same experience. Still, children who are exposed to a particular language typically arrive at a general system common to both themselves and the previous generation of speakers. Again, the data of experience do not compel the selection of any particular grammar by any particular individual, and infinitely many logically possible grammars are consistent with any finite exposure to language. Therefore, the likelihood that large numbers of individuals would acquire the same grammar (or even similar grammars) is zero, unless acquisition is subject to constraints beyond those provided by the data of experience. (Similar arguments have previously been made by several others, including Chomsky, 1965; Gold, 1967; Morgan, 1986; and Wexler & Culicover, 1980). Several additional arguments for innateness in language may be marshaled, relating to the relatively rapid and error-free nature of acquisition. Here, however, I shall note only one additional logical problem for acquisition, which I will term the problem of underspecification (see also Chomsky, 1965, and Lightfoot, 1989). Mature knowledge of language entails abilities that are not merely extrapolations from experience but that have no basis in experience whatsoever. For example, mature speakers of a language can distinguish well-formed from ill-formed sentences. Most likely, the reader will judge the Sentences 1-5 to be well-formed sentences of English but Sentence 6 to be an ill-formed sentence (the asterisk before this sentence denotes its ungrammaticality).
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(1) She thinks Gorbachev advocates reforms. (2) She thinks that Gorbachev advocates reforms. (3) What does she think Gorbachev advocates? (4) What does she think that Gorbachev advocates? (5) Who does she think advocates reforms? (6) *Who does she think that advocates reforms? In general, children are not privy to information relevant to this task. Research indicates that the speech to which children are exposed is overwhelmingly grammatical (Newport, Gleitman, & Gleitman, 1977); the ungrammatical utterances that do occur in input are not explicitly identified as such. Also, parents do not provide explicit feedback relating to the syntactic status of children’s own utterances (Brown & Hanlon, 1970; Hirsh-Pasek, Treiman, & Schneiderman, 1984). Several researchers (Bohannon & Stanowicz, 1988; Demetras, Post, & Snow, 1986; Hirsh-Pasek et al., 1984; Penner, 1987) have recently argued that parents may provide subtle cues to children’s syntactic errors, but even if this is true (see Hirsch-Pasek, Golinkoff, Braidi, & McNally, 1986, and Morgan &Travis, 1989 for counterarguments), the problem is hardly solved: the range of children’s errors is but an infinitesimal fraction of the range of possible errors. Mature speakers can judge as ill formed not only those sorts of sentences that they themselves might have produced (and been corrected on) as children but also an infinite range of sentences never before heard or spoken. At the same time, mature speakers can judge as well formed a complementary infinite range of sentences never before heard or spoken. The problems of underdetermination and underspecification jointly offer a powerful argument for the necessity of endogenous constraints on language acquisition. These constraints influence how the child attends to language input, how the child represents this input, and what sorts of inferences the child may draw on the basis of this “primary linguistic data.” Of course, one may concede the necessity of such constraints without granting that they themselves directly arise without relevant experience. The argument most often advanced in favor of this last point (cf. Chomsky, 1988) involves the notion of domain specificity: the terms in which constraints must be formulated (for example, “noun phrase” or “governing domain”-see further examples below) have no homologues in cognitive domains other than language. Hence, according to this argument, knowledge of these categories or concepts could not arise through any sort of prior nonlinguistic experience nor through any sort of general learning mechanism, and it must therefore be innate. Even if the constraints underlying language acquisition were to turn out to be completely doinain-general, however, this would not rule out their necessarily having some innate component. Presuming that there might be some sort of experience relevant to the learning of suitable domain-general constraints on acquisition (though it is unclear what might constitute such experience), these constraints would need to be learned through a process of induction, which would itself be vulnerable to the problem of underdetermination. One might hypothesize constraints on the acquisition of constraints, but the problem of underdetermination would simply regress. Ultimately, this regression must terminate in the biological constitution of the mind. The more domain-specific the constraints underlying
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I
I
advocates reforms
Fig. I .
Syntactic structure of Sentence 6.
language acquisition turn out to be, the easier it will be to argue that they are directly innate. But whether directly or indirectly, constraints on language acquisition must have some innate component.’
Why Language Is in Part Innate-Some
Specifics
How do children come to know that sentences like Sentence 6 are ungrammatical? The easiest answer is that they never encounter sentences “like” Sentence 6 while they are acquiring English. Ignoring the relatively rare instances in which ungrammatical sentences are addressed to children, there is some truth to this answer. It is also true, however, that children never encounter sentences ‘‘like’’ many of those that would be considered grammatical. Moreover, Sentence 6 appears to be very much “like” Sentences 5 or 7, both of which are grammatical. Lacking a precise definition of “like,” this easy answer is unenlightening.
(7) Who does she know that advocates reforms? Although the strings of words in Sentences 6 and 7 are very similar, syntactic analyses suggest that these two sentences have somewhat different structures. Relevant details of these structures are shown in Figures 1 and 2, respectively. Note that Sentence 6 contains an embedded sentence, “ e advocates reforms,” where e is a placeholder for the understood subject noun phrase of “advocates.” In English, embedded sentences may optionally be introduced by the complementizer eNP” is “that.” In most dialects of English, however, the sequence “that,,,, ungrammatical. In contrast, Sentence 7 contains a noun phrase containing a relative clause, “ei that ei advocates reforms.” Again, e is a placeholder for an understood noun phrase; the subscripts indicate that the two understood noun phrases refer to the same entity. In English, relative clauses may be introduced by the relativizer “that.” The sequence “that,,, cNp”is grammatical. To summarize, one aspect of the grammar of English is that the word “that” may precede an empty (understood) subject when it introduces a relative clause, as in Sentence 7, but not when it introduces an embedded sentence, as in Sentence 6. Relative
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know
N P V P
Fig. 2.
Syntactic structure of Sentence 7.
clauses and embedded sentences are defined by the different structural positions that they occupy. More generally, the categories that were required to elucidate the distinction between Sentences 6 and 7 (“sentence,” “phrase,” “subject?’ and so forth) are defined in large part in terms of particular structural configurations. For example, a subject is a noun phrase that is an immediate constituent of (is immediately dominated by) a sentence. Generalizations about syntax are most insightfully stated in terms of such structural configurations; to use Chomsky’s (1965) term, syntactic rules are “structure-dependent.” Speakers appear commonly to distinguish between sentences such as 6 and 7 without having received any relevant instruction (and in blissful ignorance of the technical labels for the structural categories involved). This suggests that language learners are generally biased to represent and analyze the sentences they encounter in terms of their structural config~rations.~
The Importance of Assuming That Language Is in Part Innate Clearly, children possess some set of psychological mechanisms that is brought to bear on language input. I have argued above that the constitution and operation of these mechanisms must be subject to constraints that are in some fashion innately determined. Without such constraints, it is not clear how children could begin to attend to relevant aspects of input, to represent the information encoded in input appropriately, or to analyze such representations in a fashion that could eventually lead to a mature grammar of the proper sort. A parallel set of observations may be made with regard to the heuristic value of assumptions of innateness for theory construction. Without assumptions of innateness (assumptions about the character of the initial state), it is difficult to see how one could embark on
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Primary Linguistic 4 Data
General learning capacities Universal grammar (Specific language faculty)
Mature grammar
exploring the problem of describing and explaining acquisition-without such assumptions, there is no principled basis for formulating hypotheses about what sorts of input experiences might be of value or for making predictions about the effects of particular experiences. Far from entailing the hypothesis that experience and learning have no effect, assumptions of innateness define what experience is relevant and how learning may proceed.
The Relationship of Innateness and Input More interesting than the question of whether assumptions of innateness should be made at all (since they appear to be unavoidable) are questions concerning the extent and nature of innate contributions to language acquisition. Answers to these questions may be approached within the framework provided by the logic of the “Language Acquisition Device” model portrayed in Figure 3. In this model, assumptions about endogenous contributions to acquisition are jointly detefmined by the characteristics of input and by the nature of the grammatical system that is the end result of acquisition. One goal of a theory of language acquisition is to link up with linguistic theory, accounting for learners’ acquisition of grammars of a particular type. Therefore, specific assumptions about what might be innate in acquisition are shaped in part by the choice of a descriptive theory of mature grammars. Whereas all grammatical theories will require assumptions concerning innate endowment, different grammatical theories require different specific assumptions about the character of this endowment, as comparison of the acquisition theories proposed by Wexler and Culicover (1980), Pinker (1984), and Lightfoot (1989)readily reveals. The decision concerning which grammatical theory to accept is (and will be) typically made on largely nondevelopmental grounds; further discussion of this issue is unfortunately beyond the scope of this essay. Assuming that a particular grammatical theory has been adopted, however, the extent and nature of assumptions about innateness in acquisition is determined in part by assumptions about the character of language input. A comparison of the learnability-theoretic models developed by Wexler and Culicover (1980) and Morgan (1986) illustrates this point. Briefly, learnability theory originates with the axiom that all normal children exposed to language necessarily acquire natural languages: natural languages are a well-defined subset of logically possible languages. The goal of a learnability-theoretic proof is to provide definitions of the character of language input and of the nature of innate constraints on the mechanisms of learning so that acquisition of natural languages follows (in theory) as a deductive consequence. Wexler and Culicover, and Morgan were concerned with models accounting for acquisition of languages generated by standard transformational grammars (see Chomsky, 1965). Wexler and Culicover assumed that the
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child’s language input consists (in part) of ungrouped strings of words. To complete their proof, Wexler and Culicover were required to adopt an extensive, specifically grammatical set of assumptions concerning innate constraints on acquisition. In contrast, Morgan assumed that, in addition to strings of words, children’s language input includes information about how words in sentences group into phrases (“bracketing information”). As a consequence of this assumption, Morgan’s proof required a significantly smaller, simpler set of assumptions on innate constraints. This comparison illustrates that, roughly speaking, the richer language input is, the weaker the innate subsidy of acquisition needs to be, and vice versa.
Arguments for Limiting Assumptions of Innateness Jointly, language input and innate constraints must supply sufficient power to ensure that language is acquired. At the present, the relative contributions of each of these components to children’s acquisition of language is largely a matter of speculation and debate. One may ask, however, whether there is any basis in principle for preferring assumptions about one of these components over assumptions about the other. In the following, 1 will present several arguments for the position that it is preferable to make overly strong assumptions about input rather than about innateness. These arguments, in overview, are the following: (a) Strong assumptions about innateness require introducing not only innateness but also maturational change to account for changes in output over development. The admission of maturation as an explanatory device, however, may make suppositions about innateness immune to disconfirmation by developmental data. (b) Strong assumptions about innateness tend to promote arbitrary relations between input and acquisition, so that claims about learnability following from such assumptions may be difficult to assess. (c) In contrast to assumptions of innateness, claims about crucial aspects of input must meet several clear acquisitional criteria and are therefore easily falsifiable. In short, I will argue that first approximations should err toward overly strong assumptions about input, because such assumptions are more testable and can more readily be modified on empirical grounds toward stronger assumptions about innateness.
A Theoretical Framework In presenting this argument, I will use examples drawn from recent literature. The points I wish to make, however, hold regardless of whether the details of these examples prove to be precisely correct. For my examples, the framework of government and binding theory, a current nativist theory, will be assumed to provide a suitable grammatical model (see Chomsky, 1981, 1986, 1988; Lightfoot, 1989). In this theory, universal grammar comprises a small set of principles and parameters. Principles capture linguistic characeristics that hold true across all languages. Parameters permit universal grammar to be adjusted to fit specific languages. Both principles and parameters are assumed to be innately given. One example of a principle of universal grammar is the principle of Phrase Composition, which states in essence that phrases are composed of an obligatory head plus an optional phrasal complement. For example, a noun phrase obligatorily
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includes a noun head (e.g., “dog” in Sentence 8) and may optionally include a prepositional phrase complement (“in the car”) and/or a relative clause complement. A prepositional phrase obligatorily includes a preposition head (e.g., “in”) and typically requires a noun phrase object (“the car”). (8) Look at
[NP
the dog
[pp
in
LNP the car111
A parameter related to this principle is the Head Order parameter: elements within phrases are ordered either head-first or head-last. In some languages, such as English, the noun precedes its complements and the preposition precedes its object; in others, Japanese for example, the noun follows its complements and the preposition follows its object (and hence is called a postposition). Each such parameter captures a dimension along which languages may vary (within or across time). The setting of a parameter often has ramifications throughout the grammar. In acquisition, some input datum or data is thought to “trigger” the setting of each parameter to the proper value for the language being learned. For example, presuming that a child hears Sentence 8 and represents the noun phrase as headplus-complement ,this would trigger the head-first setting of the Head Order Parameter. This parameter applies to all types of phrases, so that as a consequence of this triggering, in this child’s grammar, not only would noun phrases consist of noun-prepositional phrase, but also prepositional phrases would consist of preposition-object, verb phrases would consist of verb-object, and so forth.
Innateness and Maturation An informal statement of another principle of universal grammar, which 1will here term the Anaphor Binding Principle, is that anaphors must be bound within their governing domains. “Anaphors” are certain expressions such as the reflexive himself or the reciprocal each other that do not in themselves make reference to any particular entity but that instead must be linked to another phrase in the same sentence that does make such reference. For simplicity, “governing domain” here will be taken to be equivalent to “clause.” Thus, the Anaphor Binding Principle means that there must be some element within the same clause in which an anaphor appears from which the anaphor may take its reference. Sentence 9 meets this criterion: “John” and “himself” occur in the same clause, and “himself” refers to John. Sentence 10 fails to meet this criterion: “John” and “himself” occur in different clauses, and “himself” cannot refer to John; therefore, Sentence 10 is ungrammatical. (9) Mary wants lSJohn, to be proud of himselfi] (10) *Johni wants [s Mary to be proud of himself,]
Recall that principles of universal grammar are assumed to be innate. If this is correct, then a prediction about children’s language acquisition follows straightforwardly: children’s language should be consistent with the Anaphor Binding Principle at all points of development. This prediction has been tested by Matthei (1981), who investigated 4- to 6-year-old children’s interpretations of sentences like Sentence I 1 . Assuming the Anaphor Binding Principle to be correct, children
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should never interpret Sentence 11 as a paraphrase of Sentence 12: in 11, each other is not in the same clause as the boys and therefore cannot refer to the boys, whereas in 12, each other is in the same clause and must refer to the boys. Contrary to these predictions, however, Matthei found that almost two thirds of the time, children did interpret sentences like 11 as paraphrases of sentences like 12. Do these data indicate that the Anaphor Binding Principle is not innate? (1 1) (12)
The boys said that [the girls were sending notes to each other], [The boys and the girls sent notes to each other],
Lightfoot (1982) has argued that they do not, suggesting that children who interpreted Sentence 11 as equivalent to Sentence 12 may have failed to represent each other as an anaphor. However, the construct “anaphor” is defined by the Anaphor Binding Principle; the theory affords no independent means of assessing whether himselfand each other are anaphors. Thus, Lightfoot’s objection is without force, unless one proposes other grounds on which to verify the status of each other as an anaphor, independent of the status of the Anaphor Binding Principle. There is another tactic by means of which the Anaphor Binding Principle may be preserved in the face of Matthei’s data. Innateness, particularly in the sense of “arising without relevant experience” that I have adopted here, need not entail presence from birth; few objections are raised, for example, to the claim that mature sexual characteristics are in part genetically determined, even though they do not begin to develop until puberty. In this case, the Anaphor Binding Principle may be maturationally activated at some point after age six. On this view, Matthei simply tested subjects who were too young. If he had tested adults’ judgments, the Anaphor Binding Principle would have been confirmed. The difficulty with maturation as an explanatory deyice is that there is often no means of assessing maturational hypotheses independent of the particular developmental phenomenon in question. Without such means, invoking maturity whenever a principle of grammar appears to fail on developmental data can make such principles immune from falsification. In principle, the parameter setting model ought to afford such independent tests, as the ripening of a principle (or the setting of a parameter) should have diverse effects throughout a nascent grammar. For example, setting of the Head Position Parameter should affect not only noun phrases but at the same time also verb phrases, prepositional phrases, and adjectival phrases. In practice, however, such independent evidence may be hard to come by, as the manifestation of the effects of the ripening of a given principle may depend upon interactions with other principles and parameters. Alternatively, maturational hypotheses could make cross-linguistic predictions: a particular principle ought to mature at the same stage regardless of the language that is being learned (see Demuth, 1989, for an example of cross-linguistic investigation of a maturation hypothesis). Again, however, manifestation of the effects of the ripening of a given principle may well depend upon interactions with other principles and parameters, and may thus emerge at differing developmental points depending upon idiosyncratic characteristics of the language being learned. So long as maturational explanations are freely invoked without strict insistence upon independent justification, it is difficult to conceive of how hypotheses of innateness can be disconfirmed by developmental data.
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Innateness and Relations between Input and Acquisition Recall that the setting of a parameter, such as the Head Order Parameter, is triggered by exposure to some appropriate input data, such as Sentence 8 . In the case of the Head Order Parameter, the relationship between the triggering data and the content of the parameter is reasonably transparent. For other parameters, however, the relationship between the triggering data and the content of the parameter may be quite opaque. In principle, for any given parameter, languages may be divided into complementary sets. Assuming that the trigger for any given parameter is consistent across languages, any overt characteristic whatsoever that is shared by all and only those languages in a particular set can then serve as a trigger for the parameter, regardless of the transparency of the relationship between this characteristic and the nature of the parameter. No logical a priori constraints on this relationship exist. Hyams (1987) provides an example of a trigger that is opaquely related to the parameter whose setting it causes. The parameter of interest, the Null Subject Parameter, has to do with whether the subjects of sentences are always required to be overt. In some languages, like English, subjects must be expressed, as in Sentences 13 and 14. In other languages, like Italian o r Chinese, subjects are optional, as in the Italian examples, Sentences 15 and 16. (13) (14) (15) (16)
1 speak English. It is raining. Parlo italiano. ( = [I] speak Italian.) Piove. ( = [it] rains.)
H yams notes that languages that allow optional subjects have uniformly present or absent inflectional marking in their verb paradigms. Italian verbs have inflections for every possible combination of person, number, and tense; subjects are optional in Italian. Chinese verbs have only one form for all combinations of person, number, and tense; subjects are optional in Chinese. In contrast. languages that do not allow optional subjects have nonuniform inflectional marking in their verb paradigms-some verb forms are inflected but others are not. In the case of English, verbs are inflected for number only in the third person singular form; subjects are obligatory in English. Thus, verb inflection nonuniformity may serve as the triggering data for the Null Subject Parameter (default expectations of uniform inflections and optional subjects ensure that the parameter can be set correctly on the basis of positive examples only). For example, the data in Paradigm 17 might be sufficient to trigger the proper setting of the parameter for English. Note that the relationship between uniformity of verb morphology and optional subjects is quite opaque. (17)
1 run. We run. He runs.
The solution outlined above is perfectly countenanced by the parameter-setting theory. Aside from considerations of accuracy of linguistic description, this theory provides no basis for preferring one potential trigger over any others. Because the
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parameter-setting theory is strongly innate, it has forsaken several traditional sources of constraint that could contribute to a metric for choosing between potential triggers. One such source of constraint involves observations of similarity of development across domains. The parameter-setting model, however, is a domain-specific model. Given this model, patterns that may be observed in learning in other domains, such as effects of similarity or frequency, simply have no relevance to the domain of language acquisition. In a modular theory of mind, each cognitive domain may have entirely unique constraints on induction and computation; any resemblances across domains are purely coincidental. On this view the study of language cannot provide a window on the mind at large, but can only illuminate that portion of the mind directly engaged in the acquisition and use of language. Another traditional source of constraint on the relation between input and acquisition involves the assumption that the language learner’s errors have special status in prompting developmental change. In many learning models (for example, Wexler & Culicover, 1980), modifications to the learner’s internal grammar are made only when some input datum is inconsistent with that grammar, thus revealing an error; no changes occur when the input and the internal grammar are compatible. When an error is revealed, the learner’s grammar is modified so that the error-revealing datum can be generated, thus ensuring a direct relationship between the datum and the ensuing modification. In contrast, no such discrepancy is required for the setting of a parameter: Paradigm 17 could trigger the setting of the Null Subject parameter to “obligatory subject,” even though these data are perfectly consistent with the “optional subject” setting. One of the concerns of learnability-theoretic treatments of language acquisition has been to develop assumptions of input and innateness that allow acquisition to proceed on the basis of relatively simple data (simple sentences of the sort children are exposed to; see Morgan, 1986). If arbitrarily opaque relations between triggers and parameters are allowed, however, it then becomes probable that some reasonably simple input data can always be found that distinguishes languages that differ in the setting of a given parameter, regardless of the formulation of the parameter. It matters little whether such data is related to the parameter in any intuitive fashion. In consequence, claims about learnability from simple data may not be falsifiable. In turn, this means that no learnability-theoretic basis for distinguishing between versions of the parameter-setting model exists. Ironically, then, although the parameter-setting model purports to account for language acquisition, this model is not readily susceptible to test by acquisitional data derived from either developmental or learnability-theoretic methods of inquiry. Grammatical data of the sort usually employed by linguistic theorists may be useful in determining whether assumptions of innateness incorporated in a model are sufficient for providing descriptive power. The nativist assumptions of the parameter-setting model are so powerful, however, that acquisitional data are here made irrelevant, even those concerning the nature of language input, which are ordinarily especially useful for determining whether specific assumptions of innateness are necessary. Arguments similar to those above could be constructed for other strongly nativist models of language. In short, on the basis of psychological data, it may be
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impossible to discover errors introduced by excessively powerful assumptions of innateness. Assumptions about input, however, are unlikely to lead to this predicament.
An Alternative to Innateness: Invariants of Input The acquisition model illustrated in Figure 3 entails that the richer the input is, the weaker assumptions of innateness need be. Not all aspects of input are relevant here, however. Putative innate constraints or biases apply with complete generality and therefore cannot be offset by aspects of input that vary across children. For example, certain assumptions of innateness are based on the premise that children are not corrected for their grammatical errors. Findings that some children receive correction for some errors would not weigh against such assumptions, as they would still be required for those children who do not receive correction and for those errors that are not corrected. Similarly, it is unlikely that research attempting to relate variability of properties of input to the rate of language development (for example, Newport et al., 1977) can illuminate the required extent of innate constraints on acquisition. This is because even though some aspect of input may be related to acquisition of a given area of grammar, so that relatively high frequencies in input expedite learning, children’s innate endowment must still be powerful enough to ensure eventual learning given the lowest possible frequencies in input. The aspects of input that can offset assumptions of innateness are those that are invariant. If some information invariably appears in input (or at least invariably occurs in input in those situations in which the target language possesses a particular characteristic), then that information may serve in lieu of preprogramming to support acquisition. The more extensive the invariants of input are, the less powerful innate constraints on acquisition need be. Several criteria apply in determining whether some type of information is an invariant necessary aspect of input. First, the candidate information must be shown to have a clear logical relation to specific acquisitional outcomes. Second, it must be demonstrated that the information is universally available in applicable language-learning situations. Third, it must be shown that children can attend to and represent the information in some appropriate fashion. Finally, demonstration of consequences for acquisition that cannot be accounted for on other grounds supplies clinching evidence for the necessity of the candidate information. In practice, this final proof will often be unattainable, because innate constraints can almost always be devised to mimic the contributions of input. Even so, the first three criteria afford ample room for falsification of any necessary-input hypothesis. What might be an invariant characteristic of language input? Recall that I suggested above that language learners are biased to represent and analyze the sentences they encounter in terms of their structural configurations. Implicit in this is the notion that learners can assign appropriate structural representations to particular sentences. On the assumption that input comprises strings of words, complex theoretical apparatus is required to explain how this might be accomplished (see Pinker, 1984). As an alternative view, in several works (Morgan, 1986; Morgan, Meier, tk Newport, 1987, 1989; Morgan & Newport, 1981), my colleagues and I have advanced the claim that information pertaining to the grouping of words
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into phrases is a crucial characteristic of input; on this assumption, bracketed representations can be assigned more or less directly (see also Gleitman & Wanner, 1982, and Hirsh-Pasek et al., 1987). The assumption of bracketing information as an invariant of language input appears to satisfy several of the criteria set out above. As discussed earlier (see the relationship of innateness and input), bracketing information can be shown (in theory) to serve in lieu of several otherwise necessary, specifically grammatical assumptions of innateness (Morgan, 1986). Linguistic observations indicate that natural languages regularly incorporate multiple devices that encode bracketing information, including pauses and other aspects of prosody, function words (articles, prepositions, and so forth), and concord morphology (for example, rhyming word endings in Latin; see Morgan et al., 1987). Measurements of speech addressed to children confirm the availability and salience of prosodic bracketing cues in English language input (Bernstein Ratner, 1986; Morgan, 1986). Recent work by Hirsh-Pasek et al. (1987) has suggested that infants are sensitive to the prosodic cues that encode bracketing information, and Goodsitt (1986) provides data indicating that infants can indeed bracket simple input sequences. Finally, a series of studies using miniature language methodology (Morgan et al., 1987, 1989; Morgan & Newport, 1981) has indicated that adult language learners completely succeed in acquiring syntax only when bracketing information is available in input. Note that these findings do not confirm that bracketing information is an invariant aspect of language input, but contrary findings at any step would disconfirm this hypothesis. Unlike assumptions of innateness, assumptions of invariants in input are richly susceptible to empirical disconfirmation. Moreover, the research noted above has revealed ways in which bracketing information is encoded, capacities that infants possess for perceiving such information, and consequences of the availability of bracketing information for acquisition, none of which would have been readily apparent from a more cursory examination. This constitutes another argument against making assumptions of innateness in the absence of empirical investigation of language-learning situations. One point remains to be clarified: the relationship between invariant aspects of language input and innate constraints on acquisition is not one of simple reciprocity. Suppose, for the sake of argument, that the data turn out to robustly support the bracketing information hypothesis. In this case, certain specifically grammatical constraints on acquisition that might otherwise be needed could be relaxed or abolished entirely. In their place, however, other endogenous capacities would need to be posited. At minimum, children would have to be biased to attend to cues that encode bracketing information in input, and they would have to be able to assign proper interpretations to these cues. Thus, shifting theoretical power toward input will not result in the elimination of innate constraints on acquisition, although this move may change the nature of theoretically required innate contributions, so that they may be more likely to be perceptual or cognitive-domain-general and therefore more susceptible to test by traditional sorts of psychological data.
Conclusion Given the inductive nature of language acquisition, assumptions of innateness cannot be avoided. Indeed, insofar as admitting such assumptions tends to encour-
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age greater explicitness in theories of acquisition, they should be readily welcomed. In the ahsence of explicit theories of the capacities that the child brings to bear on the task of learning a language, it is unclear how to formulate hypotheses bearing on relations between input and outcome. At this point, however, relatively little is known about the nature or the extent of native constraints on language acquisition. Making overly powerful assumptions about innateness ought to be avoided, both because such assumptions may be immune to disconfirmation and because they may divert attention from investigation of language input. Formulation of a coherent theory of invariant characteristics of input is a critical prerequisite to a more complete understanding of the role of innateness in language acquisition.
Notes
’
Arising, that is, at some point in the course of development. Whether constraints on acquisition are present at birth or come about through maturation is subject to debate. Below, I will discuss some explanatory problems that arise if the possibility of maturation is admitted. Arguments for innateness based on consideration of underdetermination and underspecification have been developed primarily in the context of inductive (hypothesis-testing or parameter-setting) theories of acquisition. One might argue that if induction is an inaccurate learning model, then the need for innate constraints is obviated. This does not appear to be true, however, Rumelhart and McClelland (l986), for example, have proposed a connectionist account of children’s acquisition of past-tense verb forms that is decidedly not an induction model (see Pinker & Prince, 1987, for extensive critical discussion of this account). The model that Rumelhart and McClelland develop is a network whose input comprises present-tense forms of verbs and whose output comprises related past-tense forms. Input for the model consists of paired present-tense and past-tense verbs, with each individual form represented as a series of “Wicklephones” (triples of phonological segments). The model rests crucially upon these two assumptions about input and representation. It is unclear, however, how present-tense and past-tense forms of verbs come to be related (in children’s experiences these are usually not neatly paired) and how the Wicklephone representation is chosen. Inasmuch as modes of representation are dependent upon inductive conclusions concerning what the interesting or important aspects of input are, arguments for the necessity of innate constraints apply here as well. Several theoretical treatments have advanced explanations for the contrast in grammaticality between Sentences 6 and 7 , including Perlmutter (1971), Chomsky and Lasnik (1977), and Jacobson (1987). The critical point here is that this contrast regardless of how it might be explained, is based on the strrrcturul properties of the sentences in question. Very many examples encompassing different types of constructions could be adduced to support this same point; see Crain and Nakayama (1988).
*
’
Preparation of this paper was supported in part by National lnstitute of Child Health and Human Development Grant T32-HD0715 1 to the Center for Research in Learning, Perception, and Cognition, University of Minnesota. I thank Elissa Newport, Kathy Hirsh-Pasek, and an anonymous reviewer for their helpful comments on an earlier draft, as well as Patricia Zukow and Cathy Dent. I also thank John Dolan for organizing an interdisciplinary seminar on language and mind that provided me with an opportunity to rethink my views on innateness and Mike Maratsos for discussions of several of the issues involved.
References Bernstein R. N. (1986). Durational cues which mark clause boundaries in mother-child speech. Phonerics. 14. 303-309. Bohannon, J. N., and Stanowicz, L. (1988). The issue ofnegative evidence. DeuelopmentalPsychology, 24. 684-689. Brown. R., & Hanlon, C. (1970). Derivational complexity and the order of acquisition of child speech. In J . R. Hayes (Ed.), Cognition and the development of lunguuge (pp. 11-53). New York: Wiley. Chomsky, N . (1965). Aspects of the rheory ofsyntax. Cambridge: MIT Press.
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Chomsky, N. (1981). Lectures on government and binding. Dordrecht: Foris. Chomsky, N . (1986). Knowledge of language: Its nature, origin, and use. New York: Praeger. Chomsky, N. (1988). Language and problems of knowledge. Cambridge: MIT Press. Chomsky, N., & Lasnik, H. (1977). Filters and control. Linguistic Inquiry, 8, 425-504. Crain, S . , & Nakayama, M. (1988). Structure dependence in grammar formation. Language, 63, 522-543. Curtiss, S. (1977).Genie:A psycholinguistic study of a modern-day “wild child.” New York: Academic Press. Demetras, M. J., Post, K. N., & Snow, C. E . (1986). Feedback to first language learners: The role of repetitions and clarification questions. Journal of Child Language, 13, 275-292. Demuth, K. (1989). Maturation and the acquisition of the Sesotho passive. Language, 65, 56-80. Feldman, H., Goldin-Meadow, S., & Gleitman, L. R. (1978). Beyond Herodotus: The creation of language by linguistically deprived deaf children. In A. Lock (Ed.), Action, symbol, and gesture: The emergence of language (pp. 351-414). New York: Academic Press. Gleitman, L. R., & Wanner, E . (1982). Language learning: State of the art. In E. Wanner & L. R. Gleitman (Eds.), Language acquisition: The state of the art (pp. 3-48). Cambridge: Harvard University Press. Gold, E. M. (1967). Language identification in the limit. Information and Control, 10, 447-474. Goldin-Meadow, S. (1982). The resilience of recursion: A study of a communication system developed without a conventional language model. In E. Wanner & L . R. Gleitman (Eds.), Language acquisition: The state of the art (pp. 51-77). Cambridge: Harvard University Press. Goldin-Meadow, S., & Mylander, C. (1984). Gestural communication in deaf children: The effects and noneffects of parental input on early language development. Monographs of the Society for Research in Child Development, Serial No. 207, 49, Nos. 3-4. Goodman, N. (1983). Fact, fiction, andforecast. Cambridge: Harvard University Press. Goodsitt, J. V. (1986). The unitization of syllabic sequences b y language learning infants. Unpublished Ph.D. dissertation, University of Minnesota. Hirsh-Pasek, K., Golinkoff, R. M., Braidi, S. M., & McNally, L. (1986). “Daddy throw”: On the existence of implicit negative evidence for subcategorization errors. Presented at the Boston University Conference on Child Language Development, October. Hirsh-Pasek, K., Kemler Nelson, D. G., Jusczyk, P. W., Cassidy, K. W., Druss, B., & Kennedy, L. (1987). Clauses are perceptual units for young infants. Cognition, 26, 269-286. Hirsh-Pasek, K., Treiman, R., & Schneiderman, M. (1984). Brown & Hanlon revisited: Mother’s sensitivity to ungrammatical forms. Journal of Child Language, 11, 81-88. Hyams, N. (1987). The setting of the null subject parameter: A reanalysis. Paper presented at the Boston University Conference on Child Language Development, October. Jacobson, P. (1987). Review of Gazdar, Klein, Pullum, & Sag, Generalizedphrase structure grammar. Linguistics and Philosophy, 10, 389-426. Lane, H. (1976). The wild boy of Aveyron. Cambridge: Harvard University Press. Lightfoot, D. (1982). The language lottery: Toward a biology of grammars. Cambridge: MIT Press. Lightfoot, D. (1989). The child’s trigger experience: “Degree-0’’ learnability. Behavioral and Brain Sciences, 12, 321-334. Maratsos, M. P. (1986). Crosslinguistic analysis, universals, and language acquisition. In F . S. Kessel (Ed.), The development oflanguage and language researchers (pp. 121-152). Hillsdale: Erlbaum. Matthei, E . H. (1981). Children’s interpretations of sentences containing reciprocals. In S . L. Tavakolian (Ed.), Language acquisition and linguistic theory, 97-1 15. Cambridge: MIT Press. McNeill, D. (1966). Developmental psycholinguistics. In F. Smith & G. A. Miller (Eds.), The genesis of language (pp. 15-84). Cambridge: MIT Press. Morgan, J. L. (1986). From simple input to complex grammar. Cambridge: MIT Press. Morgan, J. L., Meier, R. P., & Newport, E. L.(1987). Structural packaging in the input to language learning: Contributions of prosodic and morphological marking of phrases to the acquisition of language. Cognitive Psychology, 19, 498-550. Morgan, J. L., Meier, R. P., & Newport, E. L. (1989). Facilitating the acquisition of syntax with transformational cues to phrase structure. Journal of Memory and Language, 28, 360-374. Morgan, J. L., & Newport, E. L. (1981). The role of constituent structure in the induction of an artificial language. Journal of Verbal Learning and Verbal Behavior, 20, 67-85. Morgan, J . L., & Travis, L. L. (1989). Limits on negative information in language input. Journal of Child Language, 16, 531-552.
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Newport, E. L., Gleitman, H., & Gleitman, L. R. (1977). Mother, I’d rather do it myself Some effects and non-effects of material speech style. In C. E. Snow & C. A. Ferguson (Eds.), Talking to children (pp. 109-149). Cambridge: Cambridge University Press. Oyama, S. (in press). Ontogeny and the central dogma: Do we need the concept ofgenetic programming in order to have an evolutionary perspective? In M. E. Gunnar (Ed.), Proceedings ofthe Minnesota Symposium on Child Development, Vol. 22. Penner, S. G. (1987). Parental responses to grammatical and ungrammatical child utterances. Child Development, 58, 376-384. Perlmutter, D. (1971). Deep and surface structure constraints in syntax. New York: Holt, Rinehart & Winston. Pinker, S. (1984). Language learnability and language development. Cambridge: Harvard University Press. Pinker, S . , & Prince, A. (1987). On language and connectionism: Analysis of a parallel distributed processing model of language acquisition. Cognition, 28, 73-193. Rumelhart. D. E., & McClelland, J. L. (1986). On learning the past tenses of English verbs. In J. L. McClelland, D. E. Rumelhart, and the PDP Research Group, Parallel distributed processing: Explorations in the microstructure of cognition. Vol. 2: Psychological and biological models. Cambridge: MIT Press. Wexler, K.. & Culicover, P. W. (1980). Formal principles of language acquisition. Cambridge: MIT Press.
Input and innateness compliment one another in language acquisition. Children exposed to different languages acquire different languages. Children’s language experience, however, underdetermines the grammars that they acquire; the constraints that are not supplied by input must be available endogenously, and the ultimate origin of these endogenous contributions to acquisition may be traced to the biology of the mind. To the extent that assumptions of innateness encourage greater explicitness in the formulation of theories of acquisition, they should be welcomed. Excessively powerful assumptions of innateness may not be subject to empirical disconfirmation, however. Therefore, attention should be devoted to the development of a theory of language input, particularly with regard to identifying invariants of input. In combination with a linguistic theory providing an account of the endstate of acquisition, a theory of input would permit the deduction of properties of the mind that underlie the acquisition of language.
Language is the product of the child’s attending to, representing, and analyzing linguistically relevant input in a fashion sanctioned by imperatives of human nature. This interactional position is acceded to by virtually all theorists, including strong nativists such as Chomsky, who, in outlining the goals of the study of language, has written: We must determine how the child comes to master the rules and principles that constitute the mature system of knowledge of language. The problem is an empirical one. In principle, the source of such knowledge might lie in the child’s environment or in the biologically determined resources of the mindlbrain, specifically, that component of the mind/brain that we might call the language faculty; interaction of these factors provides the system of knowledge that is put to use in speaking and understanding. (1988, p. 15)
In this article, I advocate an intermediate position on the question of innateness in language acquisition. Several arguments lead irresistibly to the conclusion that Reprint requests should be sent to Dr. James L. Morgan, Department of Cognitive and Linguistic Sciences, Brown University, Box 1978, Providence, Rhode Island 02912. Received for publication 1 September 1988 Revised for publication 30 August 1989 Accepted at Wiley 13 July 1990 Deuelopmentnl Psychobiology 23(7):661-678 (1990) 0 1990 by John Wiley & Sons, Inc.
CCC 0012-1630/90/070661- 18$04.00
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acquisition could not proceed without preprogramming. If the descriptions provided by present-day linguistic theories come anywhere close to being psychologically valid (these theories at any rate provide insightful and wide-ranging accounts of the truly formidable intricacies of natural language), then the extent of required preprogramming may be substantial indeed. Nevertheless, admitting innateness into the explanatory armamentorium does not exclude learning: language is not innate OY learned; language is innate and learned. On this view, the key theoretical issue is how to apportion explanatory responsibility between input and innateness. At present, this decision is largely uninformed by empirical findings. I argue, however, that strong assumptions about input should be favored in principle. My argument hinges on differences in vulnerability to disproof between assumptions of input and innateness. Strong assumptions of innateness may not be subject to empirical disconfirmation by the very acquisitional data that they purport to predict and explain. In contrast, it is easy to identify the sort of acquisitional data that would require strong assumptions about input to be abandoned. In the following, I develop these arguments concerning input, innateness, and induction in language acquisition.
Why Language Is in Part Learned The reason why language must be learned is obvious. There are very many different languages in existence, and (with some interesting exceptions including creolization and other instances of generational change) every child systematically succeeds in acquiring the very language (or languages) to which he or she is exposed, regardless of whether this might be the child’s genetically ancestral language. Insofar as any language is a system that relates sounds (or gestures) to meaning, critical components of such exposure-language input-must include hearing (or seeing) examples of the language and having access to the context, physical and social, in which these examples are used, so that their meanings may be educed. The child’s task, then, is to represent and analyze this input, learning which sounds are possible, how sounds may combine with one another to form morphemes or words, what morphemes mean, how words may be combined to form phrases and sentences, what social factors govern appropriateness of particular expressions, and so forth.
Why Language Is in Part Innate-a
General Argument
The reasons why language must be innate are perhaps more subtle, but they are no less compelling. The debate on innateness in language has been muddied somewhat by confusion over both what might be supposed to be innate about language and what is meant by the term “innate.” As Oyama (in press) has noted, “innate” has a history of being used rather loosely as a rubric for several overlapping claims about the origin and nature of behavior. These include having evolutionary history, being species typical, having a genetic basis, being adaptive, being present from birth, arising without relevant experience, occurring independently of the environment, and having a rigid or stereotyped form. Virtually all of these have been advanced by one side or another in the debate over the innateness
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of language. The appropriateness of any particular definition, however, depends upon the precise nature of what is claimed to be innate in language. Claims about innate aspects of language have been made at several different levels of analysis, varying in abstractness. Most concretely, the forms or functions of particular linguistic expressions could be innate. Alternatively, specific aspects of the linguistic knowledge underlying linguistic expressions-one’s grammar-could be innately determined. Most abstractly, the particular learning capacities through which linguistic knowledge is acquired could be innate. I will discuss each of these in turn. The notion that particular overt aspects of language might be innate has a long tradition; here, the sense of “innate” as behavior displaying “rigid or stereotyped form” seems to be most germane. This notion is implicit at several points in Genesis, from the Garden of Eden (Adam’s naming of animals) to the Tower of Babel. Feldman, Goldin-Meadow, and Gleitman (1978) recount a tale from Herodotus in which two monarchs agreed to decide a dispute concerning the primacy of their kingdoms by having two children raised in strict isolation. The dispute was resolved when the children uttered some words in the language of one of the kingdoms, which was thereupon conceded to be the more ancient. King James I is reputed to have conducted a similar experiment, the subject of which supposedly acquired Hebrew. Despite these colorful tales, however, no serious evidence exists to support the view that specific manifestations of language are innately determined. In the literature on feral and isolated children, there is only one example of a child who exhibited any speech upon discovery; further investigation has suggested that this particular child (allegedly the bastard son of a Prussian monarch) was actually held in captivity for several years and trained to utter two or three sentences (Lane, 1976). Others subjected to the cruel natural experiment of social isolation have failed to invent language spontaneously (see Curtiss, 1977, for an account of the modern-day case of Genie). The view that certain aspects of grammar, including rules, relations, and categories of language, might be innate has several modern advocates (see especially McNeill, 1966). Here, “innate” in the sense of “species typical” (or “language universal”) is most relevant. Certainly, some grammatical elements do appear to be universal: languages have a basic unit, the clause, that is used to express propositions-propositions are composed of a predicate and one or more arguments. Distinct classes of words are canonically used to denote predicates and arguments; and one clause may be embedded within another. Investigations of children who are linguistically, but not socially, isolated-deaf children of nonsigning parents-suggest that some of these elements may develop in the absence of relevant linguistic input (for details see Goldin-Meadow, 1982, and Goldin-Meadow & Mylander, 1984). The inventory of universal elements of grammar, however, may be quite limited. Maratsos (1986) argues that the category noun is unique in manifesting common cross-linguistic characteristics; the remaining categories that are usually taken to be most basic, verb, adjective, and preposition, are grouped in virtually all possible combinations in form classes of specific languages. In addition, whereas Chomsky (1986) has argued that there is a universal structural definition of the primary relational category subject, whose acquisition by children is guided by innate principles, Maratsos (1986) has argued that subject lacks any cross-linguistic core of features that would enable its structural properties
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to be discovered. For present purposes, suffice it to say that whether the specific rules, relations, and categories of any given language are innate is a matter of considerable debate. The most unassailable case for innateness, to my mind, may be made at the third and most abstract level of analysis, with respect to the capacities for representing and analyzing input that underlie children’s acquisition of grammars. Here, the sense of “innate” as “arising without relevant experience” is most apt.’ Several considerations argue for the need for constraints on learning in acquisition beyond those that might be supplied by children’s language input. Foremost among these is the logical problem of induction-namely, that for any child, the available input necessarily underdetermines the grammatical system that is acquired (see Goodman, 1983, for a more general discussion of this logical problem). Knowing a language entails being able to produce and comprehend an unlimited number of sentences; yet each child’s linguistically relevant experience is finite. The child must arrive at some sort of general grammatical system based on this finite experience. The logical problem of induction, however, is that there are infinitely many general patterns compatible with any finite range of data, and, hence, the data do not determine the choice of any particular generalization. With respect to language, there are infinitely many (logically possible) grammars compatible with any finite exposure to language, but no such exposure forces the choice of any particular grammar. Nevertheless, individuals who share knowledge of a particular language are able to produce or comprehend more or less the same range of sentences and therefore have arrived at more or less the same generalizations about (or have acquired more or less the same grammar of) that language. (Readers who would dispute this assertion should note that they were able to comprehend the previous sentence, even though it was undoubtedly novel to them. This would not be possible unless they shared with me notions of what constitutes English.) No two children share precisely the same experience. Still, children who are exposed to a particular language typically arrive at a general system common to both themselves and the previous generation of speakers. Again, the data of experience do not compel the selection of any particular grammar by any particular individual, and infinitely many logically possible grammars are consistent with any finite exposure to language. Therefore, the likelihood that large numbers of individuals would acquire the same grammar (or even similar grammars) is zero, unless acquisition is subject to constraints beyond those provided by the data of experience. (Similar arguments have previously been made by several others, including Chomsky, 1965; Gold, 1967; Morgan, 1986; and Wexler & Culicover, 1980). Several additional arguments for innateness in language may be marshaled, relating to the relatively rapid and error-free nature of acquisition. Here, however, I shall note only one additional logical problem for acquisition, which I will term the problem of underspecification (see also Chomsky, 1965, and Lightfoot, 1989). Mature knowledge of language entails abilities that are not merely extrapolations from experience but that have no basis in experience whatsoever. For example, mature speakers of a language can distinguish well-formed from ill-formed sentences. Most likely, the reader will judge the Sentences 1-5 to be well-formed sentences of English but Sentence 6 to be an ill-formed sentence (the asterisk before this sentence denotes its ungrammaticality).
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(1) She thinks Gorbachev advocates reforms. (2) She thinks that Gorbachev advocates reforms. (3) What does she think Gorbachev advocates? (4) What does she think that Gorbachev advocates? (5) Who does she think advocates reforms? (6) *Who does she think that advocates reforms? In general, children are not privy to information relevant to this task. Research indicates that the speech to which children are exposed is overwhelmingly grammatical (Newport, Gleitman, & Gleitman, 1977); the ungrammatical utterances that do occur in input are not explicitly identified as such. Also, parents do not provide explicit feedback relating to the syntactic status of children’s own utterances (Brown & Hanlon, 1970; Hirsh-Pasek, Treiman, & Schneiderman, 1984). Several researchers (Bohannon & Stanowicz, 1988; Demetras, Post, & Snow, 1986; Hirsh-Pasek et al., 1984; Penner, 1987) have recently argued that parents may provide subtle cues to children’s syntactic errors, but even if this is true (see Hirsch-Pasek, Golinkoff, Braidi, & McNally, 1986, and Morgan &Travis, 1989 for counterarguments), the problem is hardly solved: the range of children’s errors is but an infinitesimal fraction of the range of possible errors. Mature speakers can judge as ill formed not only those sorts of sentences that they themselves might have produced (and been corrected on) as children but also an infinite range of sentences never before heard or spoken. At the same time, mature speakers can judge as well formed a complementary infinite range of sentences never before heard or spoken. The problems of underdetermination and underspecification jointly offer a powerful argument for the necessity of endogenous constraints on language acquisition. These constraints influence how the child attends to language input, how the child represents this input, and what sorts of inferences the child may draw on the basis of this “primary linguistic data.” Of course, one may concede the necessity of such constraints without granting that they themselves directly arise without relevant experience. The argument most often advanced in favor of this last point (cf. Chomsky, 1988) involves the notion of domain specificity: the terms in which constraints must be formulated (for example, “noun phrase” or “governing domain”-see further examples below) have no homologues in cognitive domains other than language. Hence, according to this argument, knowledge of these categories or concepts could not arise through any sort of prior nonlinguistic experience nor through any sort of general learning mechanism, and it must therefore be innate. Even if the constraints underlying language acquisition were to turn out to be completely doinain-general, however, this would not rule out their necessarily having some innate component. Presuming that there might be some sort of experience relevant to the learning of suitable domain-general constraints on acquisition (though it is unclear what might constitute such experience), these constraints would need to be learned through a process of induction, which would itself be vulnerable to the problem of underdetermination. One might hypothesize constraints on the acquisition of constraints, but the problem of underdetermination would simply regress. Ultimately, this regression must terminate in the biological constitution of the mind. The more domain-specific the constraints underlying
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I
I
advocates reforms
Fig. I .
Syntactic structure of Sentence 6.
language acquisition turn out to be, the easier it will be to argue that they are directly innate. But whether directly or indirectly, constraints on language acquisition must have some innate component.’
Why Language Is in Part Innate-Some
Specifics
How do children come to know that sentences like Sentence 6 are ungrammatical? The easiest answer is that they never encounter sentences “like” Sentence 6 while they are acquiring English. Ignoring the relatively rare instances in which ungrammatical sentences are addressed to children, there is some truth to this answer. It is also true, however, that children never encounter sentences ‘‘like’’ many of those that would be considered grammatical. Moreover, Sentence 6 appears to be very much “like” Sentences 5 or 7, both of which are grammatical. Lacking a precise definition of “like,” this easy answer is unenlightening.
(7) Who does she know that advocates reforms? Although the strings of words in Sentences 6 and 7 are very similar, syntactic analyses suggest that these two sentences have somewhat different structures. Relevant details of these structures are shown in Figures 1 and 2, respectively. Note that Sentence 6 contains an embedded sentence, “ e advocates reforms,” where e is a placeholder for the understood subject noun phrase of “advocates.” In English, embedded sentences may optionally be introduced by the complementizer eNP” is “that.” In most dialects of English, however, the sequence “that,,,, ungrammatical. In contrast, Sentence 7 contains a noun phrase containing a relative clause, “ei that ei advocates reforms.” Again, e is a placeholder for an understood noun phrase; the subscripts indicate that the two understood noun phrases refer to the same entity. In English, relative clauses may be introduced by the relativizer “that.” The sequence “that,,, cNp”is grammatical. To summarize, one aspect of the grammar of English is that the word “that” may precede an empty (understood) subject when it introduces a relative clause, as in Sentence 7, but not when it introduces an embedded sentence, as in Sentence 6. Relative
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know
N P V P
Fig. 2.
Syntactic structure of Sentence 7.
clauses and embedded sentences are defined by the different structural positions that they occupy. More generally, the categories that were required to elucidate the distinction between Sentences 6 and 7 (“sentence,” “phrase,” “subject?’ and so forth) are defined in large part in terms of particular structural configurations. For example, a subject is a noun phrase that is an immediate constituent of (is immediately dominated by) a sentence. Generalizations about syntax are most insightfully stated in terms of such structural configurations; to use Chomsky’s (1965) term, syntactic rules are “structure-dependent.” Speakers appear commonly to distinguish between sentences such as 6 and 7 without having received any relevant instruction (and in blissful ignorance of the technical labels for the structural categories involved). This suggests that language learners are generally biased to represent and analyze the sentences they encounter in terms of their structural config~rations.~
The Importance of Assuming That Language Is in Part Innate Clearly, children possess some set of psychological mechanisms that is brought to bear on language input. I have argued above that the constitution and operation of these mechanisms must be subject to constraints that are in some fashion innately determined. Without such constraints, it is not clear how children could begin to attend to relevant aspects of input, to represent the information encoded in input appropriately, or to analyze such representations in a fashion that could eventually lead to a mature grammar of the proper sort. A parallel set of observations may be made with regard to the heuristic value of assumptions of innateness for theory construction. Without assumptions of innateness (assumptions about the character of the initial state), it is difficult to see how one could embark on
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Primary Linguistic 4 Data
General learning capacities Universal grammar (Specific language faculty)
Mature grammar
exploring the problem of describing and explaining acquisition-without such assumptions, there is no principled basis for formulating hypotheses about what sorts of input experiences might be of value or for making predictions about the effects of particular experiences. Far from entailing the hypothesis that experience and learning have no effect, assumptions of innateness define what experience is relevant and how learning may proceed.
The Relationship of Innateness and Input More interesting than the question of whether assumptions of innateness should be made at all (since they appear to be unavoidable) are questions concerning the extent and nature of innate contributions to language acquisition. Answers to these questions may be approached within the framework provided by the logic of the “Language Acquisition Device” model portrayed in Figure 3. In this model, assumptions about endogenous contributions to acquisition are jointly detefmined by the characteristics of input and by the nature of the grammatical system that is the end result of acquisition. One goal of a theory of language acquisition is to link up with linguistic theory, accounting for learners’ acquisition of grammars of a particular type. Therefore, specific assumptions about what might be innate in acquisition are shaped in part by the choice of a descriptive theory of mature grammars. Whereas all grammatical theories will require assumptions concerning innate endowment, different grammatical theories require different specific assumptions about the character of this endowment, as comparison of the acquisition theories proposed by Wexler and Culicover (1980), Pinker (1984), and Lightfoot (1989)readily reveals. The decision concerning which grammatical theory to accept is (and will be) typically made on largely nondevelopmental grounds; further discussion of this issue is unfortunately beyond the scope of this essay. Assuming that a particular grammatical theory has been adopted, however, the extent and nature of assumptions about innateness in acquisition is determined in part by assumptions about the character of language input. A comparison of the learnability-theoretic models developed by Wexler and Culicover (1980) and Morgan (1986) illustrates this point. Briefly, learnability theory originates with the axiom that all normal children exposed to language necessarily acquire natural languages: natural languages are a well-defined subset of logically possible languages. The goal of a learnability-theoretic proof is to provide definitions of the character of language input and of the nature of innate constraints on the mechanisms of learning so that acquisition of natural languages follows (in theory) as a deductive consequence. Wexler and Culicover, and Morgan were concerned with models accounting for acquisition of languages generated by standard transformational grammars (see Chomsky, 1965). Wexler and Culicover assumed that the
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child’s language input consists (in part) of ungrouped strings of words. To complete their proof, Wexler and Culicover were required to adopt an extensive, specifically grammatical set of assumptions concerning innate constraints on acquisition. In contrast, Morgan assumed that, in addition to strings of words, children’s language input includes information about how words in sentences group into phrases (“bracketing information”). As a consequence of this assumption, Morgan’s proof required a significantly smaller, simpler set of assumptions on innate constraints. This comparison illustrates that, roughly speaking, the richer language input is, the weaker the innate subsidy of acquisition needs to be, and vice versa.
Arguments for Limiting Assumptions of Innateness Jointly, language input and innate constraints must supply sufficient power to ensure that language is acquired. At the present, the relative contributions of each of these components to children’s acquisition of language is largely a matter of speculation and debate. One may ask, however, whether there is any basis in principle for preferring assumptions about one of these components over assumptions about the other. In the following, 1 will present several arguments for the position that it is preferable to make overly strong assumptions about input rather than about innateness. These arguments, in overview, are the following: (a) Strong assumptions about innateness require introducing not only innateness but also maturational change to account for changes in output over development. The admission of maturation as an explanatory device, however, may make suppositions about innateness immune to disconfirmation by developmental data. (b) Strong assumptions about innateness tend to promote arbitrary relations between input and acquisition, so that claims about learnability following from such assumptions may be difficult to assess. (c) In contrast to assumptions of innateness, claims about crucial aspects of input must meet several clear acquisitional criteria and are therefore easily falsifiable. In short, I will argue that first approximations should err toward overly strong assumptions about input, because such assumptions are more testable and can more readily be modified on empirical grounds toward stronger assumptions about innateness.
A Theoretical Framework In presenting this argument, I will use examples drawn from recent literature. The points I wish to make, however, hold regardless of whether the details of these examples prove to be precisely correct. For my examples, the framework of government and binding theory, a current nativist theory, will be assumed to provide a suitable grammatical model (see Chomsky, 1981, 1986, 1988; Lightfoot, 1989). In this theory, universal grammar comprises a small set of principles and parameters. Principles capture linguistic characeristics that hold true across all languages. Parameters permit universal grammar to be adjusted to fit specific languages. Both principles and parameters are assumed to be innately given. One example of a principle of universal grammar is the principle of Phrase Composition, which states in essence that phrases are composed of an obligatory head plus an optional phrasal complement. For example, a noun phrase obligatorily
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includes a noun head (e.g., “dog” in Sentence 8) and may optionally include a prepositional phrase complement (“in the car”) and/or a relative clause complement. A prepositional phrase obligatorily includes a preposition head (e.g., “in”) and typically requires a noun phrase object (“the car”). (8) Look at
[NP
the dog
[pp
in
LNP the car111
A parameter related to this principle is the Head Order parameter: elements within phrases are ordered either head-first or head-last. In some languages, such as English, the noun precedes its complements and the preposition precedes its object; in others, Japanese for example, the noun follows its complements and the preposition follows its object (and hence is called a postposition). Each such parameter captures a dimension along which languages may vary (within or across time). The setting of a parameter often has ramifications throughout the grammar. In acquisition, some input datum or data is thought to “trigger” the setting of each parameter to the proper value for the language being learned. For example, presuming that a child hears Sentence 8 and represents the noun phrase as headplus-complement ,this would trigger the head-first setting of the Head Order Parameter. This parameter applies to all types of phrases, so that as a consequence of this triggering, in this child’s grammar, not only would noun phrases consist of noun-prepositional phrase, but also prepositional phrases would consist of preposition-object, verb phrases would consist of verb-object, and so forth.
Innateness and Maturation An informal statement of another principle of universal grammar, which 1will here term the Anaphor Binding Principle, is that anaphors must be bound within their governing domains. “Anaphors” are certain expressions such as the reflexive himself or the reciprocal each other that do not in themselves make reference to any particular entity but that instead must be linked to another phrase in the same sentence that does make such reference. For simplicity, “governing domain” here will be taken to be equivalent to “clause.” Thus, the Anaphor Binding Principle means that there must be some element within the same clause in which an anaphor appears from which the anaphor may take its reference. Sentence 9 meets this criterion: “John” and “himself” occur in the same clause, and “himself” refers to John. Sentence 10 fails to meet this criterion: “John” and “himself” occur in different clauses, and “himself” cannot refer to John; therefore, Sentence 10 is ungrammatical. (9) Mary wants lSJohn, to be proud of himselfi] (10) *Johni wants [s Mary to be proud of himself,]
Recall that principles of universal grammar are assumed to be innate. If this is correct, then a prediction about children’s language acquisition follows straightforwardly: children’s language should be consistent with the Anaphor Binding Principle at all points of development. This prediction has been tested by Matthei (1981), who investigated 4- to 6-year-old children’s interpretations of sentences like Sentence I 1 . Assuming the Anaphor Binding Principle to be correct, children
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should never interpret Sentence 11 as a paraphrase of Sentence 12: in 11, each other is not in the same clause as the boys and therefore cannot refer to the boys, whereas in 12, each other is in the same clause and must refer to the boys. Contrary to these predictions, however, Matthei found that almost two thirds of the time, children did interpret sentences like 11 as paraphrases of sentences like 12. Do these data indicate that the Anaphor Binding Principle is not innate? (1 1) (12)
The boys said that [the girls were sending notes to each other], [The boys and the girls sent notes to each other],
Lightfoot (1982) has argued that they do not, suggesting that children who interpreted Sentence 11 as equivalent to Sentence 12 may have failed to represent each other as an anaphor. However, the construct “anaphor” is defined by the Anaphor Binding Principle; the theory affords no independent means of assessing whether himselfand each other are anaphors. Thus, Lightfoot’s objection is without force, unless one proposes other grounds on which to verify the status of each other as an anaphor, independent of the status of the Anaphor Binding Principle. There is another tactic by means of which the Anaphor Binding Principle may be preserved in the face of Matthei’s data. Innateness, particularly in the sense of “arising without relevant experience” that I have adopted here, need not entail presence from birth; few objections are raised, for example, to the claim that mature sexual characteristics are in part genetically determined, even though they do not begin to develop until puberty. In this case, the Anaphor Binding Principle may be maturationally activated at some point after age six. On this view, Matthei simply tested subjects who were too young. If he had tested adults’ judgments, the Anaphor Binding Principle would have been confirmed. The difficulty with maturation as an explanatory deyice is that there is often no means of assessing maturational hypotheses independent of the particular developmental phenomenon in question. Without such means, invoking maturity whenever a principle of grammar appears to fail on developmental data can make such principles immune from falsification. In principle, the parameter setting model ought to afford such independent tests, as the ripening of a principle (or the setting of a parameter) should have diverse effects throughout a nascent grammar. For example, setting of the Head Position Parameter should affect not only noun phrases but at the same time also verb phrases, prepositional phrases, and adjectival phrases. In practice, however, such independent evidence may be hard to come by, as the manifestation of the effects of the ripening of a given principle may depend upon interactions with other principles and parameters. Alternatively, maturational hypotheses could make cross-linguistic predictions: a particular principle ought to mature at the same stage regardless of the language that is being learned (see Demuth, 1989, for an example of cross-linguistic investigation of a maturation hypothesis). Again, however, manifestation of the effects of the ripening of a given principle may well depend upon interactions with other principles and parameters, and may thus emerge at differing developmental points depending upon idiosyncratic characteristics of the language being learned. So long as maturational explanations are freely invoked without strict insistence upon independent justification, it is difficult to conceive of how hypotheses of innateness can be disconfirmed by developmental data.
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Innateness and Relations between Input and Acquisition Recall that the setting of a parameter, such as the Head Order Parameter, is triggered by exposure to some appropriate input data, such as Sentence 8 . In the case of the Head Order Parameter, the relationship between the triggering data and the content of the parameter is reasonably transparent. For other parameters, however, the relationship between the triggering data and the content of the parameter may be quite opaque. In principle, for any given parameter, languages may be divided into complementary sets. Assuming that the trigger for any given parameter is consistent across languages, any overt characteristic whatsoever that is shared by all and only those languages in a particular set can then serve as a trigger for the parameter, regardless of the transparency of the relationship between this characteristic and the nature of the parameter. No logical a priori constraints on this relationship exist. Hyams (1987) provides an example of a trigger that is opaquely related to the parameter whose setting it causes. The parameter of interest, the Null Subject Parameter, has to do with whether the subjects of sentences are always required to be overt. In some languages, like English, subjects must be expressed, as in Sentences 13 and 14. In other languages, like Italian o r Chinese, subjects are optional, as in the Italian examples, Sentences 15 and 16. (13) (14) (15) (16)
1 speak English. It is raining. Parlo italiano. ( = [I] speak Italian.) Piove. ( = [it] rains.)
H yams notes that languages that allow optional subjects have uniformly present or absent inflectional marking in their verb paradigms. Italian verbs have inflections for every possible combination of person, number, and tense; subjects are optional in Italian. Chinese verbs have only one form for all combinations of person, number, and tense; subjects are optional in Chinese. In contrast. languages that do not allow optional subjects have nonuniform inflectional marking in their verb paradigms-some verb forms are inflected but others are not. In the case of English, verbs are inflected for number only in the third person singular form; subjects are obligatory in English. Thus, verb inflection nonuniformity may serve as the triggering data for the Null Subject Parameter (default expectations of uniform inflections and optional subjects ensure that the parameter can be set correctly on the basis of positive examples only). For example, the data in Paradigm 17 might be sufficient to trigger the proper setting of the parameter for English. Note that the relationship between uniformity of verb morphology and optional subjects is quite opaque. (17)
1 run. We run. He runs.
The solution outlined above is perfectly countenanced by the parameter-setting theory. Aside from considerations of accuracy of linguistic description, this theory provides no basis for preferring one potential trigger over any others. Because the
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parameter-setting theory is strongly innate, it has forsaken several traditional sources of constraint that could contribute to a metric for choosing between potential triggers. One such source of constraint involves observations of similarity of development across domains. The parameter-setting model, however, is a domain-specific model. Given this model, patterns that may be observed in learning in other domains, such as effects of similarity or frequency, simply have no relevance to the domain of language acquisition. In a modular theory of mind, each cognitive domain may have entirely unique constraints on induction and computation; any resemblances across domains are purely coincidental. On this view the study of language cannot provide a window on the mind at large, but can only illuminate that portion of the mind directly engaged in the acquisition and use of language. Another traditional source of constraint on the relation between input and acquisition involves the assumption that the language learner’s errors have special status in prompting developmental change. In many learning models (for example, Wexler & Culicover, 1980), modifications to the learner’s internal grammar are made only when some input datum is inconsistent with that grammar, thus revealing an error; no changes occur when the input and the internal grammar are compatible. When an error is revealed, the learner’s grammar is modified so that the error-revealing datum can be generated, thus ensuring a direct relationship between the datum and the ensuing modification. In contrast, no such discrepancy is required for the setting of a parameter: Paradigm 17 could trigger the setting of the Null Subject parameter to “obligatory subject,” even though these data are perfectly consistent with the “optional subject” setting. One of the concerns of learnability-theoretic treatments of language acquisition has been to develop assumptions of input and innateness that allow acquisition to proceed on the basis of relatively simple data (simple sentences of the sort children are exposed to; see Morgan, 1986). If arbitrarily opaque relations between triggers and parameters are allowed, however, it then becomes probable that some reasonably simple input data can always be found that distinguishes languages that differ in the setting of a given parameter, regardless of the formulation of the parameter. It matters little whether such data is related to the parameter in any intuitive fashion. In consequence, claims about learnability from simple data may not be falsifiable. In turn, this means that no learnability-theoretic basis for distinguishing between versions of the parameter-setting model exists. Ironically, then, although the parameter-setting model purports to account for language acquisition, this model is not readily susceptible to test by acquisitional data derived from either developmental or learnability-theoretic methods of inquiry. Grammatical data of the sort usually employed by linguistic theorists may be useful in determining whether assumptions of innateness incorporated in a model are sufficient for providing descriptive power. The nativist assumptions of the parameter-setting model are so powerful, however, that acquisitional data are here made irrelevant, even those concerning the nature of language input, which are ordinarily especially useful for determining whether specific assumptions of innateness are necessary. Arguments similar to those above could be constructed for other strongly nativist models of language. In short, on the basis of psychological data, it may be
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impossible to discover errors introduced by excessively powerful assumptions of innateness. Assumptions about input, however, are unlikely to lead to this predicament.
An Alternative to Innateness: Invariants of Input The acquisition model illustrated in Figure 3 entails that the richer the input is, the weaker assumptions of innateness need be. Not all aspects of input are relevant here, however. Putative innate constraints or biases apply with complete generality and therefore cannot be offset by aspects of input that vary across children. For example, certain assumptions of innateness are based on the premise that children are not corrected for their grammatical errors. Findings that some children receive correction for some errors would not weigh against such assumptions, as they would still be required for those children who do not receive correction and for those errors that are not corrected. Similarly, it is unlikely that research attempting to relate variability of properties of input to the rate of language development (for example, Newport et al., 1977) can illuminate the required extent of innate constraints on acquisition. This is because even though some aspect of input may be related to acquisition of a given area of grammar, so that relatively high frequencies in input expedite learning, children’s innate endowment must still be powerful enough to ensure eventual learning given the lowest possible frequencies in input. The aspects of input that can offset assumptions of innateness are those that are invariant. If some information invariably appears in input (or at least invariably occurs in input in those situations in which the target language possesses a particular characteristic), then that information may serve in lieu of preprogramming to support acquisition. The more extensive the invariants of input are, the less powerful innate constraints on acquisition need be. Several criteria apply in determining whether some type of information is an invariant necessary aspect of input. First, the candidate information must be shown to have a clear logical relation to specific acquisitional outcomes. Second, it must be demonstrated that the information is universally available in applicable language-learning situations. Third, it must be shown that children can attend to and represent the information in some appropriate fashion. Finally, demonstration of consequences for acquisition that cannot be accounted for on other grounds supplies clinching evidence for the necessity of the candidate information. In practice, this final proof will often be unattainable, because innate constraints can almost always be devised to mimic the contributions of input. Even so, the first three criteria afford ample room for falsification of any necessary-input hypothesis. What might be an invariant characteristic of language input? Recall that I suggested above that language learners are biased to represent and analyze the sentences they encounter in terms of their structural configurations. Implicit in this is the notion that learners can assign appropriate structural representations to particular sentences. On the assumption that input comprises strings of words, complex theoretical apparatus is required to explain how this might be accomplished (see Pinker, 1984). As an alternative view, in several works (Morgan, 1986; Morgan, Meier, tk Newport, 1987, 1989; Morgan & Newport, 1981), my colleagues and I have advanced the claim that information pertaining to the grouping of words
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into phrases is a crucial characteristic of input; on this assumption, bracketed representations can be assigned more or less directly (see also Gleitman & Wanner, 1982, and Hirsh-Pasek et al., 1987). The assumption of bracketing information as an invariant of language input appears to satisfy several of the criteria set out above. As discussed earlier (see the relationship of innateness and input), bracketing information can be shown (in theory) to serve in lieu of several otherwise necessary, specifically grammatical assumptions of innateness (Morgan, 1986). Linguistic observations indicate that natural languages regularly incorporate multiple devices that encode bracketing information, including pauses and other aspects of prosody, function words (articles, prepositions, and so forth), and concord morphology (for example, rhyming word endings in Latin; see Morgan et al., 1987). Measurements of speech addressed to children confirm the availability and salience of prosodic bracketing cues in English language input (Bernstein Ratner, 1986; Morgan, 1986). Recent work by Hirsh-Pasek et al. (1987) has suggested that infants are sensitive to the prosodic cues that encode bracketing information, and Goodsitt (1986) provides data indicating that infants can indeed bracket simple input sequences. Finally, a series of studies using miniature language methodology (Morgan et al., 1987, 1989; Morgan & Newport, 1981) has indicated that adult language learners completely succeed in acquiring syntax only when bracketing information is available in input. Note that these findings do not confirm that bracketing information is an invariant aspect of language input, but contrary findings at any step would disconfirm this hypothesis. Unlike assumptions of innateness, assumptions of invariants in input are richly susceptible to empirical disconfirmation. Moreover, the research noted above has revealed ways in which bracketing information is encoded, capacities that infants possess for perceiving such information, and consequences of the availability of bracketing information for acquisition, none of which would have been readily apparent from a more cursory examination. This constitutes another argument against making assumptions of innateness in the absence of empirical investigation of language-learning situations. One point remains to be clarified: the relationship between invariant aspects of language input and innate constraints on acquisition is not one of simple reciprocity. Suppose, for the sake of argument, that the data turn out to robustly support the bracketing information hypothesis. In this case, certain specifically grammatical constraints on acquisition that might otherwise be needed could be relaxed or abolished entirely. In their place, however, other endogenous capacities would need to be posited. At minimum, children would have to be biased to attend to cues that encode bracketing information in input, and they would have to be able to assign proper interpretations to these cues. Thus, shifting theoretical power toward input will not result in the elimination of innate constraints on acquisition, although this move may change the nature of theoretically required innate contributions, so that they may be more likely to be perceptual or cognitive-domain-general and therefore more susceptible to test by traditional sorts of psychological data.
Conclusion Given the inductive nature of language acquisition, assumptions of innateness cannot be avoided. Indeed, insofar as admitting such assumptions tends to encour-
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age greater explicitness in theories of acquisition, they should be readily welcomed. In the ahsence of explicit theories of the capacities that the child brings to bear on the task of learning a language, it is unclear how to formulate hypotheses bearing on relations between input and outcome. At this point, however, relatively little is known about the nature or the extent of native constraints on language acquisition. Making overly powerful assumptions about innateness ought to be avoided, both because such assumptions may be immune to disconfirmation and because they may divert attention from investigation of language input. Formulation of a coherent theory of invariant characteristics of input is a critical prerequisite to a more complete understanding of the role of innateness in language acquisition.
Notes
’
Arising, that is, at some point in the course of development. Whether constraints on acquisition are present at birth or come about through maturation is subject to debate. Below, I will discuss some explanatory problems that arise if the possibility of maturation is admitted. Arguments for innateness based on consideration of underdetermination and underspecification have been developed primarily in the context of inductive (hypothesis-testing or parameter-setting) theories of acquisition. One might argue that if induction is an inaccurate learning model, then the need for innate constraints is obviated. This does not appear to be true, however, Rumelhart and McClelland (l986), for example, have proposed a connectionist account of children’s acquisition of past-tense verb forms that is decidedly not an induction model (see Pinker & Prince, 1987, for extensive critical discussion of this account). The model that Rumelhart and McClelland develop is a network whose input comprises present-tense forms of verbs and whose output comprises related past-tense forms. Input for the model consists of paired present-tense and past-tense verbs, with each individual form represented as a series of “Wicklephones” (triples of phonological segments). The model rests crucially upon these two assumptions about input and representation. It is unclear, however, how present-tense and past-tense forms of verbs come to be related (in children’s experiences these are usually not neatly paired) and how the Wicklephone representation is chosen. Inasmuch as modes of representation are dependent upon inductive conclusions concerning what the interesting or important aspects of input are, arguments for the necessity of innate constraints apply here as well. Several theoretical treatments have advanced explanations for the contrast in grammaticality between Sentences 6 and 7 , including Perlmutter (1971), Chomsky and Lasnik (1977), and Jacobson (1987). The critical point here is that this contrast regardless of how it might be explained, is based on the strrrcturul properties of the sentences in question. Very many examples encompassing different types of constructions could be adduced to support this same point; see Crain and Nakayama (1988).
*
’
Preparation of this paper was supported in part by National lnstitute of Child Health and Human Development Grant T32-HD0715 1 to the Center for Research in Learning, Perception, and Cognition, University of Minnesota. I thank Elissa Newport, Kathy Hirsh-Pasek, and an anonymous reviewer for their helpful comments on an earlier draft, as well as Patricia Zukow and Cathy Dent. I also thank John Dolan for organizing an interdisciplinary seminar on language and mind that provided me with an opportunity to rethink my views on innateness and Mike Maratsos for discussions of several of the issues involved.
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