| Poverty Of The Stimulus |
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SUMMARY OF THE ARGUMENT Though Chomsky reiterated the argument in a variety of different manners, one common structure to the argument can be summed up as follows: # There are certain patterns in natural (i.e. human) languages that need to be explained. # These patterns cannot be learned by language learners (children) using positive evidence alone. '''Positive evidence''' is the set of grammatical sentences the language learner has access to, i.e. 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. # Children are only ever presented with positive evidence for these particular patterns, e.g. they only hear others speaking using sentences that are "right," not those that are "wrong". # Children do learn the correct grammars for their native languages. ; Conclusion : ''Therefore'', human beings must have some form of innate linguistic capacity which provides additional knowledge to language learners. EVIDENCE 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 four 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. The first is the hierarchical nature of languages. The Grammar s of human languages produce Hierarchichal Tree Structures and are capable of Infinite Recursion (see Context-free Grammar ). As it would apply to APS, this point is well accepted, and it is the foundation of Generative Linguistics . For any given set of sentences generated by a hierarchichal grammar capable of infinite recursion there are an indefinite number of grammars which could have produced the same data. That too is unquestioned. Based on a formal proof by E. Gold , it has been claimed that any language which has hierarchical structure capable of infinite recursion is unlearnable from positive evidence alone. But, see below for criticism. Another 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). 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, linked below, for the complete account and critique.) 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 four 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. CRITIQUES OF THE ARGUMENT Though recognized as valid, the Soundness of the poverty of stimulus argument is widely questioned. Indeed, every one of the four premises of the argument has been questioned at some point in time. A lot of the criticism comes from researchers who study Language Acquisition and Computational Linguistics . As well, Connectionist researchers have never accepted most of Chomsky's premises, because they are at odds with connectionist beliefs about the structure of cognition. Below are some of the most common critiques of the premises: As for the first case of an unlearnable language pattern, based on Gold's research, it's not clear that human languages are truly capable of infinite recursion. After all, no one has ever witnessed a sentence infnitely long. Psycholinguistic experiments show that people find 4 or more layers of recursion quite confusing. Chomsky and his supporters have argued that this is an issue of performance, not competence, and that the lack of deep recursion in natural language is merely due to constraints on mechanisms such as Working Memory . Critics respond that this removes the Falsifiability of the premise, rendering it unscientific. Besides that, Gold's research, which was more mathematical and less linguistic, doesn't even bear on the linguistic question. 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. (See Johnson 2004). There is also criticism about whether negative evidence is really so rarely encountered by children. For the case of subject-auxiliary inversion, see Pullum (1996) (linked below) for why learners probably do get negative evidence of the rule. In addition, if one allows for statistical learning, negative evidence is abound. Consider that if a language pattern is never encountered, but it's probability of being encountered were it true is very high, then the language learner might be right in considering the pattern ungrammatical even without explicitly being told so. A problem with APS is that it doesn't say just how much needs to be innate for these linguistic patterns to be within reach. Researchers using Neural Networks and other Statistical methods have extracted hierarchical structures from positive data alone. SEE ALSO EXTERNAL LINKS
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