The Theory of Poverty of the Stimulus in Language Development

In language studies, poverty of the stimulus is the argument that the linguistic input received by young children is in itself insufficient to explain their detailed knowledge of their first language, so people must be born with an innate ability to learn a language. 

Origins

An influential advocate of this controversial theory has been linguist Noam Chomsky, who introduced the expression "poverty of the stimulus" in his Rules and Representations (Columbia University Press, 1980). The concept is also known as an argument from the poverty of the stimulus (APS), logical problem of language acquisition, projection problem, and Plato's problem. 

The poverty of the stimulus argument has also been used to reinforce Chomsky's theory of universal grammar, the thought that all languages have some tenets in common. 

Poverty of the Stimulus vs. Behaviorism

The concept contrasts with the behaviorist idea that children learn language through rewards—when they are understood, their needs are met. When they make a mistake, they are corrected. Chomsky contends that children learn language too quickly and with too few structural errors to have to have every possible variation rewarded or punished before they learn the proper structure, so some part of the ability to learn language must be innate to help them automatically skip over making some errors.

For example, in English, some rules, sentence structures or usages are applied inconsistently, done in some situations and not others. Children are not taught all of the nuances as to when they might apply a particular rule and when they might not (a poverty of that particular stimulus) yet they'll correctly choose the appropriate time to apply that rule.

Problems With Each Theory

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Universal Grammar (UG)

By Richard Nordquist

Problems with the poverty of the stimulus theory include that it's difficult to define what constitutes "enough" modeling of a grammatical concept for children to effectively have it learned (i.e., the core thought that children haven't received "enough" modeling of a particular concept). Problems with the behaviorist theory are that improper grammar can also be rewarded, but children work out what is correct regardless.

Here are some examples of famous works of literature and other texts.

Plato's Problem

"[H]ow comes it that human beings, whose contacts with the world are brief and personal and limited, are nevertheless able to know as much as they do know?"
(Bertrand Russell, Human Knowledge: Its Scope and Limits. George Allen & Unwin, 1948)

Wired for Language?

"[H]ow is it that children ... routinely succeed in learning their mother tongues? The input is patchy and defective: parental speech does not seem to provide a very satisfactory, neat and tidy model from which children could easily derive the underlying rules...

"Because of this apparent poverty of the stimulus--the fact that linguistic knowledge seems undetermined by the input available for learning; many linguists have claimed in recent years that some knowledge of language must be 'wired in.' We must, the argument goes, be born with a theory of language. This hypothesized genetic endowment provides children with prior information about how languages are organized, so that, once exposed to linguistic input, they can immediately start fitting the details of their particular mother tongue into a ready-made framework, rather than cracking the code from scratch without guidance."
(Michael Swan, Grammar. Oxford University Press, 2005)

Chomsky's Position

"It is, for the present, impossible to formulate an assumption about initial, innate structure rich enough to account for the fact that grammatical knowledge is attained on the basis of the evidence available to the learner."
(Noam Chomsky, Aspects of the Theory of Syntax. MIT, 1965)

Steps in the Poverty-of-the-Stimulation Argument

"There are four steps to the poverty-of-the-stimulation argument (Cook, 1991):

"Step A: A native speaker of a particular language knows a particular aspect of syntax...
"Step B: This aspect of syntax could not have been acquired from the language input typically available to children...
"Step C: We conclude that this aspect of syntax is not learnt from outside...
"Step D: We deduce that this aspect of syntax is built into the mind."
(Vivian James Cook and Mark Newson, Chomsky's Universal Grammar: An Introduction, 3rd ed. Blackwell, 2007)

Linguistic Nativism

"Language acquisition presents some unusual characteristics. ... First, languages are very complex and hard for adults to learn. Learning a second language as an adult requires a significant commitment of time, and the end result generally falls well short of native proficiency. Second, children learn their first languages without explicit instruction, and with no apparent effort. Third, the information available to the child is fairly limited. He/she hears a random subset of short sentences. The putative difficulty of this learning task is one of the strongest intuitive arguments for linguistic nativism. It has become known as The Argument from the Poverty of the Stimulus (APS)."
(Alexander Clark and Shalom Lappin, Linguistic Nativism and the Poverty of the Stimulus. Wiley-Blackwell, 2011)

Challenges to the Poverty-of-the-Stimulus Argument

"[O]pponents of Universal Grammar have argued that the child has much more evidence than Chomsky thinks: among other things, special modes of speech by parents ('Motherese') that make linguistic distinctions clearer to the child (Newport et al. 1977; Fernald 1984), understanding of context, including social context (Bruner 1974/5; Bates and MacWhinney 1982), and statistical distribution of phonemic transitions (Saffran et al. 1996) and of word occurrence (Plinkett and Marchman 1991). All these kinds of evidence are indeed available to the child, and they do help. Chomsky makes a telling slip here, when he says (1965: 35), 'Real progress in linguistics consists in the discovery that certain features of given languages can be reduced to universal properties of language, and explained in terms of these deeper aspects of linguistic form.' He neglects to observe that it is also real progress to show that there is evidence enough in the input for certain features of languages to be learned."
(Ray Jackendoff, Foundations of Language: Brain, Meaning, Grammar, Evolution. Oxford Univ. Press, 2002)