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This double issue attempts to review and understand the pros and cons of the ‘poverty of stimulus’ argument. This argument has found its way to the fore-front of the generative literature as the hallmark testimony for the notion that language is inherently innate in humans.

This article examines a type of argument for linguistic nativism that takes the following form: (i) a fact about some natural language is exhibited that allegedly could not be learned from experience without access to a certain kind of (positive) data; (ii) it is claimed that data of the type in question are not found in normal linguistic experience; hence (iii) it is concluded that people cannot be learning the language from mere exposure to language use. We analyze the components of this sort of argument carefully, and examine four exemplars, none of which hold up. We conclude that linguists have some additional work to do if they wish to sustain their claims about having provided support for linguistic nativism, and we offer some reasons for thinking that the relevant kind of future work on this issue is likely to further undermine the linguistic nativist position.

‘The poverty of the stimulus’ is a key concept within generative linguistics. This article attempts in three ways to better understand the nature of that concept and the context of its use: first, by narrating its history from the late 1950s to the present day; second, by analyzing the properties of a family of terms (including “the poverty of the stimulus”) which generativists have developed to refer to the relationship between input to language learners and their linguistic competence; and third, by examining some examples of how “the poverty of the stimulus” has been differently construed in recent discourse about linguistics and about language acquisition.

The common-sense layman's assumption would be that the structure of the languages which people grow up speaking reflects the properties of the language-samples they hear. There is no good reason to dispute that. Pullum and Scholz see their own discussion as open to the criticism that their examples are drawn from genres which are untypical of the speech encountered by young children. Accordingly, I examine the evidence of a four-million-word sample of spontaneous everyday conversation; this, too, refutes the claims about usage made by poverty-of-stimulus theorists. Widespread current acceptance of the poverty-of-stimulus idea has apparently come about not because linguists have found the contrary view empirically unsatisfactory, but merely because poverty of the stimulus is for one reason or another treated as an unquestioned axiom. A related issue is lack of negative evidence. It is true that children acquiring their mother tongue encounter only positive examples. But in this respect the logic of language-acquisition is no different from that of scientific discovery. ‘Poverty of the stimulus’ seems plausible to linguists who believe that human beings inherit detailed knowledge about language structure. But that belief is itself grossly implausible. The languages of the world are too diverse to be the product of an innate language faculty. If language structure is not in any substantial respect innate, then children's experience of their elders' language must be adequate for language-learning; the evidence suggests that that is so.

The argument from the poverty of the stimulus as Pullum and Scholz define it (their APS) is undeniably true, given that all language learners acquire the ability to generate more sentences of the target language than they have heard. Uniformity across learners with respect to the additional sentences they project suggests that grammar induction is guided by general principles, which must be innate. What remains to be established is exactly which sentences can be projected on the basis of which others. The details of this are important to linguistic theory and to the psycho-computational modelling of natural language acquisition. They are not of great significance to the generic issue of nativism versus empiricism, except that they may clarify the extent to which the innate knowledge in question is specific to language. The argument for linguistic nativism appears to be solidly supported by the distinctive patterns of generalization that learners adopt in the absence of systematic negative evidence (a limitation that Pullum and Scholz exclude from APS). We argue that innate knowledge of how to represent natural language facts is necessary in order for learners to extract from their input the information that it does contain. Pullum and Scholz themselves rely on Universal Grammar in just this role when they make specific suggestions as to how learners arrive at the right generalizations.

Positive data involving auxiliary fronting are never evidence for a constraint such as the structure-dependent hypothesis. At best, positive data of any complexity are direct evidence for a simple-minded hypothesis, of the sort of ‘front the first auxiliary (after something or other)’. On the widespread assumption that negative data are generally unavailable to children learning language, a serious empiricist alternative to the rationalist view that linguistic structure is partly innate would have to show how the correct hypothesis (‘front the matrix auxiliary’) is induced from mere extensions from positive data. But this does not seem possible.

It is a fact that the child learner does not entertain logically possible but empirically impossible linguistic hypotheses, despite the absence of sufficient disconfirming evidence. While Pullum & Scholz claim to have shown the existence of disconfirming evidence, they fail to demonstrate its sufficiency. By situating the acquisition problem in a quantitative and comparative framework, we show that the evidence is, after all, insufficient. Hence the argument from the poverty of the stimulus, and the innateness of linguistic knowledge, stand unchallenged.

Nativists inspired by Chomsky are apt to provide arguments with the following general form: languages exhibit interesting generalizations that are not suggested by casual (or even intensive) examination of what people actually say; correspondingly, adults (i.e., just about anyone above the age of four) know much more about language than they could plausibly have learned on the basis of their experience; so absent an alternative account of the relevant generalizations and speakers' (tacit) knowledge of them, one should conclude that there are substantive “universal” principles of human grammar and, as a result of human biology, children can only acquire languages that conform to these principles. According to Pullum and Scholz, linguists need not suppose that children are innately endowed with “specific contingent facts about natural languages.” But Pullum and Scholz don't consider the kinds of facts that really impress nativists. Nor do they offer any plausible acquisition scenarios that would culminate in the acquisition of languages that exhibit the kinds of rich and interrelated generalizations that are exhibited by natural languages. As we stress, good poverty-of-stimulus arguments are based on specific principles – confirmed by drawing on (negative and crosslinguistic) data unavailable to children – that help explain a range of independently established linguistic phenomena. If subsequent psycholinguistic experiments show that very young children already know such principles, that strengthens the case for nativism; and if further investigation shows that children sometimes “try out” constructions that are unattested in the local language, but only if such constructions are attested in other human languages, then the case for nativism is made stronger still. We illustrate these points by considering an apparently disparate – but upon closer inspection, interestingly related – cluster of phenomena involving: negative polarity items, the interpretation of ‘or’, binding theory, and displays of Romance and Germanic constructions in Child-English.

This article is a reply to the foregoing responses to our “Empirical assessment of stimulus poverty arguments” (Pullum and Scholz, this special volume, here-after EASPA ). We first address certain philosophical themes that cut across all six responses. We correct the impression held by Lasnik and Uriagereka (L&U) and Crain and Pietroski (C&P) that EASPA owes the reader an alternative theory of language acquisition; we distinguish linguistic nativism from several alternatives, only one of them being anti-nativism as espoused by Sampson; we examine the claim of Thomas that there is an identifiable concept ‘poverty of the stimulus’ in the linguistics literature; we point out that Fodor and Crowther (F&C) appear to misunderstand certain mathematical learnability results; and we address a purported argument for nativism (quite distinct from the stimulus poverty argument we considered in EASPA) that is advanced independently by several respondents: F&C, L&U, and Legate and Yang (L&Y) – an argument based on the underdetermination of theory by evidence.