Poverty of the stimulus: Difference between revisions

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(the POTS argument is a variant of the problem?? it's a contested SOLUTION to the problem. jesus!)
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Finally, it has been argued that people may not learn the exact same grammars as each other. If this is the case, then only a weak version of the third premise is true, as there would be no fully "correct" grammar to be learned. However, in many cases, Poverty of Stimulus arguments do not in fact depend on the assumption that there is only one correct grammar, but rather that there is only one correct ''class'' of grammars. For example, the Poverty of Stimulus argument from question formation depends only on the assumption that everyone learns a ''structure-dependent'' grammar.
Finally, it has been argued that people may not learn the exact same grammars as each other. If this is the case, then only a weak version of the third premise is true, as there would be no fully "correct" grammar to be learned. However, in many cases, Poverty of Stimulus arguments do not in fact depend on the assumption that there is only one correct grammar, but rather that there is only one correct ''class'' of grammars. For example, the Poverty of Stimulus argument from question formation depends only on the assumption that everyone learns a ''structure-dependent'' grammar.
i have edited this ..

Revision as of 17:09, 11 February 2010

The poverty of the stimulus (POTS) is one of many arguments which claims that natural language grammar is unlearnable given the relatively limited data available to children learning a language, and therefore that this knowledge is supplemented with some sort of innate linguistic capacity. As such, the argument strikes against empiricist accounts of language acquisition and is usually construed as being in favor of linguistic nativism. Nativists claim that humans are born with a specific representational adaptation for language that both funds and limits their competence to acquire specific types of natural languages over the course of their cognitive development and linguistic maturation. The basic idea informs the teachings of Socrates, Plato, and the Pythagoreans, pervades the work of the Cartesian linguists and Wilhelm von Humboldt, and surfaces again with the contemporary linguistic theories of Noam Chomsky. The argument is now generally used to support theories and hypotheses of generative grammar. The name was coined by Chomsky in his work Rules and Representations.[1] The thesis emerged out of several of Chomsky's writings on the issue of language acquisition. The argument has long been controversial within linguistics, forming the empirical backbone for the theory of universal grammar.


Though Chomsky and his supporters have reiterated the argument in a variety of different manners (indeed Pullum and Scholz (2002a) provide no less than 13 different "subarguments" that can optionally form part of a poverty-of-stimulus argument),[2] one frequent structure to the argument can be summed up as follows:

  • Premises:
  1. There are patterns in all natural languages (i.e. human languages) that cannot be learned by children using positive evidence alone. Positive evidence is the set of grammatical sentences the language learner has access to, that is, by observing the speech of others. Negative evidence, on the other hand, is the evidence available to the language learner about what is not grammatical. For instance, when a parent corrects a child's speech, the child acquires negative evidence.
  2. Children are only ever presented with positive evidence for these particular patterns. For example, they only hear others speaking using sentences that are "right", not those that are "wrong".
  3. Children do learn the correct grammars for their native languages.
  • Conclusion: Therefore, human beings must have some form of innate linguistic capacity that provides additional knowledge to language learners.


For the argument

The validity of the argument itself is unquestioned. Very few people, if any, would argue that Chomsky's conclusion doesn't follow from his premises. Thus, anyone who accepts the first three propositions must accept the conclusion. Many linguists accept all of the premises and consider there to be quite a bit of evidence for them.

Several patterns in language have been claimed to be unlearnable from positive evidence alone. One example is the hierarchical nature of languages. The grammars of human languages produce hierarchical tree structures and some linguists argue that human languages are also capable of infinite recursion (see Context-free grammar). For any given set of sentences generated by a hierarchical grammar capable of infinite recursion there are an indefinite number of grammars that could have produced the same data. This would make learning any such language impossible. Indeed, a proof by E. Mark Gold showed that any formal language that has hierarchical structure capable of infinite recursion is unlearnable from positive evidence alone,[3] in the sense that it is impossible to formulate a procedure that will discover with certainty the correct grammar given any arbitrary sequence of positive data in which each utterance occurs at least once.[4] However, this does not preclude arriving at the correct grammar using typical input sequences rather than particularly malicious sequences or arrive at an almost perfect approximation to the correct grammar. Indeed, it has been proved that under very mild assumptions (ergodicity and stationarity), the probability of producing a sequence that renders language learning impossible is in fact zero.[5]

Another example of language pattern claimed to be unlearnable from positive evidence alone is subject-auxiliary inversion in questions, i.e.:

  • You are happy.
  • Are you happy?

There are two hypotheses the language learner might postulate about how to form questions: (1) The first auxiliary verb in the sentence (here: 'are') moves to the beginning of the sentence, or (2) the 'main' auxiliary verb in the sentence moves to the front. In the sentence above, both rules yield the same result since there is only one auxiliary verb. But, you can see the difference in this case:

  • Anyone who is interested can see me later.
  1. Is anyone who interested can see me later?
  2. Can anyone who is interested see me later?

Of course, the result of rule (1) is ungrammatical while the result of rule (2) is grammatical. So, rule (2) is (approximately) what we actually have in English, not rule (1). The claim, then, first is that children don't see sentences as complicated as this one enough to witness a case where the two hypotheses yield different results, and second that just based on the positive evidence of the simple sentences, children could not possibly decide between (1) and (2). Moreover, even sentences such as (1) and (2) are compatible with a number of incorrect rules (such as "front any auxiliary).[6] Thus, if rule (2) was not innately known to infants, we would expect half of the adult population to use (1) and half to use (2). Since that doesn't occur, rule (2) must be innately known. (See Pullum 1996 for the complete account and critique.)[7]

The last premise, that children successfully learn language, is considered to be evident in human speech. Though people occasionally make mistakes, human beings rarely speak ungrammatical sentences, and generally do not label them as such when they say them. (Ungrammatical in the descriptive sense, not the prescriptive sense.)

That many linguists accept all three of the premises is testimony to Chomsky's influence in the discipline, and the persuasiveness of the argument. Nonetheless, the APS has many critics, both inside and outside linguistics.

Against the argument

Though some recognize the theory as valid, the soundness of the poverty of stimulus argument is widely questioned. Indeed, every one of the three premises of the argument has been questioned at some point in time. Much of the criticism comes from researchers who study language acquisition and computational linguistics. Additionally, connectionist researchers have never accepted most of Chomsky's premises, because these premises are at odds with connectionist beliefs about the structure of cognition.

The first and most common critique, is that positive evidence is actually enough to learn the various patterns that linguists claim are unlearnable by positive evidence alone. A common argument is that the brain's mechanisms of statistical pattern recognition could solve many of the imagined difficulties. For example, researchers using neural networks and other statistical methods have programmed computers to learn rules such as (2) cited above, and have claimed to have successfully extracted hierarchical structures, all using positive evidence alone.[8][9] Indeed, Klein & Manning (2002)[10] report constructing a computer program that is able to retrieve 80% of all correct syntactic analyses of text in the Wall Street Journal Corpus using a statistical learning mechanism (unsupervised grammar induction) demonstrating a clear move away from "toy" grammars.

There is also much criticism about whether negative evidence is really so rarely encountered by children. Pullum argues that learners probably do get certain kinds of negative evidence. In addition, if one allows for statistical learning, negative evidence is abundant. Consider that if a language pattern is never encountered, but its probability of being encountered would be very high were it acceptable, then the language learner might be right in considering absence of the pattern as negative evidence.[7] Chomsky accepts that this kind of negative evidence plays a role in language acquisition, terming it "indirect negative evidence", though he does not think that indirect negative evidence is sufficient for language acquisition to proceed without Universal Grammar. However, contra this claim, Ramscar and Yarlett (2007) designed a learning model that successfully simulates the learning of irregular plurals based on negative evidence, and backed the predictions of this simulation in empirical tests of young children. Ramscar and Yarlett suggest that failures of expectation function as forms of implicit negative feedback that allow children to correct their errors.[11]

As for the argument based on Gold's proof, it's not clear that human languages are truly capable of infinite recursion. Clearly, no speaker can ever in fact produce a sentence with an infinite recursive structure, and in certain cases (for example, center embedding), people are unable to comprehend sentences with only a few levels of recursion. Chomsky and his supporters have long argued that such cases are best explained by restrictions on working memory, since this provides a principled explanation for limited recursion in language use. Some critics argue that this removes the falsifiability of the premise.[citation needed] Returning to the big picture, it is questionable whether Gold's research actually bears on the question of natural language acquisition at all, since what Gold showed is that there are certain classes of formal languages for which some language in the class cannot be learned given positive evidence alone. It's not at all clear that natural languages fall in such a class, let alone whether they are the ones that are not learnable.[12]

Another important criticism pertains to specifying the conclusion: "some form of innate linguistic capacity." All theories of language ability assume some biological component, ranging from the extensive, abstract principles of Chomsky's Universal Grammar to cognitive processes that are not specific to language (e.g., forming perceptual and conceptual categories, processing that involves statistically-based distributional analyses, and creating analogies across constructions)[13]. Thus, there are many different interpretations of the outcome of the POS argument. For example, The Oxford Handbook of Linguistic Analysis[14] provides summaries of 32 different theories, most of which are very different than Chomsky's version of generative grammar. If one does not adopt Chomsky's linguistic theory, some of the evidence for the POS argument disappears. For example, the argument that children must choose between two different rules for "moving" an auxiliary verb does not exist within most grammatical theories. The argument exists only if one adopts a transformational or derivational theory that chooses one structure (i.e. declarative) as "underlying" and then abstractly forms other structures (e.g. questions) by moving elements such as auxiliary verbs. However, many of the theories in the OHLA are monostratal or constraint-based and do not involve movement (e.g., Cognitive Grammar, Construction Grammar, Usage-Based Theory). An additional criticism of the subject-auxiliary inversion argument is the manner in which it has been expressed: "There are two hypotheses the language learner might postulate." This statement implies that preschool children are postulating and choosing between complex hypotheses about syntactic structures. This "child as linguist" claim is an imprecise metaphor that does not contribute to our understanding of developmental psychology. In sum, the Poverty of Stimulus argument has essentially no value within modern psychology and linguistics: Everyone agrees that there is some biological component to language learning. The arguments that are of much greater importance are those that lead researchers to choose among, for example, the 32 linguistic theories in the OHLA.

Finally, it has been argued that people may not learn the exact same grammars as each other. If this is the case, then only a weak version of the third premise is true, as there would be no fully "correct" grammar to be learned. However, in many cases, Poverty of Stimulus arguments do not in fact depend on the assumption that there is only one correct grammar, but rather that there is only one correct class of grammars. For example, the Poverty of Stimulus argument from question formation depends only on the assumption that everyone learns a structure-dependent grammar.

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  1. ^ Chomsky, N. (1980). Rules and representations. Oxford: Basil Blackwell.
  2. ^ Pullum, Geoffrey K., Scholz, Barbara C. (2002). Empirical assessment of stimulus poverty arguments. The Linguistic Review 19. 9–50.
  3. ^ E.M.Gold, Language Identification in the Limit, Information and Control, 10(5): 447–474, 1967
  4. ^ Gold, E. (1967). Language identification in the limit. Information and Control 10, 447–474.
  5. ^ Clark, A. (2001). "Unsupervised Language Acquisition: Theory and Practice", DPhil thesis. PDF
  6. ^ Lasnik, Howard and Juan Uriagereka. (2002). On the Poverty of the Challenge. The Linguistic Review 19. 147–150. [1]
  7. ^ a b Pullum, Geoffrey K. (1996). Learnability, hyperlearning, and the poverty of the stimulus. In Proceedings of the 22nd Annual Meeting of the Berkeley Linguistics Society: General Session and Parasession on the Role of Learnability in Grammatical Theory, ed. J. Johnson, M.L. Juge, and J.L. Moxley, 498–513. Berkeley, California. HTML Cite error: Invalid <ref> tag; name "Pullum2" defined multiple times with different content (see the help page).
  8. ^ Bates, E. and Elman J. (1996). Learning Revisited. Science 274 (5294), 1849–1850.
  9. ^ Solan, Z., Horn, D., Ruppin, E., and Edelman, S. (2005). Unsupervised learning of natural languages. Proceedings of the National Academy of Sciences 102 (33), 11629–11634.
  10. ^ Klein, D. & Manning, C. (2002). A generative constituent-context model for improved grammar induction. In Proceedings of the 40th annual meeting of the Association for Computational Linguistics. Philadelphia. 128–135.
  11. ^ Ramscar, M. & Yarlett, D. (2007) Linguistic self-correction in the absence of feedback: A new approach to the logical problem of language acquisition. Cognitive Science: 31, 927–960.
  12. ^ Johnson, Kent. (2004). Gold's theorem and cognitive science. Philosophy of Science 71, 571–592.
  13. ^ Tomasello, M. (2003). Constructing a language: A usage-based theory of language acquisition. Cambridge, Mass.: Harvard University Press.
  14. ^ Heine, B., and Narrog, H. (2009). The Oxford Handbook of Linguistic Analysis. Oxford: Oxford University Press.

Additional References

  • Chomsky, N. (1988). Language and problems of knowledge. Cambridge, Massachusetts: MIT Press.
  • Cowie, F. (2008) "Innateness and Language." Stanford Encyclopedia of Philosophy.
  • Kaplan, F., Oudeyer, P-Y and Bergen, B. (2008) Computational models in the debate over language learnabiliy, Infant and Child Development, 17 (1), 55–80.PDF
  • Marcus, Gary F. (1993). Negative evidence in language acquisition. Cognition 46 (1), 53–85.
  • Legate, Julie and Charles Yang (2002). Empirical re-assessment of stimulus poverty arguments. The Linguistic Review 19: 151–162. [2]
  • Reich, P. (1969). The finiteness of natural language. Language 45, 831–843.

See also

External links