Poverty of the Stimulus

Poverty of the Stimulus (POS) is the argument that children acquire linguistic knowledge that cannot be derived from the linguistic input they receive, therefore that knowledge must be innate. Noam Chomsky used this argument to justify Universal Grammar: if learning alone cannot explain acquisition, the child must bring prior constraints to the task.

The canonical example: children know that questions are formed by moving the auxiliary verb in the main clause ('The dog that is sleeping is hungry' → 'Is the dog that is sleeping hungry?'), not by moving the first auxiliary encountered ('*Is the dog that sleeping is hungry?'). Yet children are rarely if ever corrected for this error, because they do not make it. How do they know? Chomsky's answer: they are genetically predisposed to entertain only structure-dependent rules.

The empiricist response: the input is richer than Chomsky assumed. Statistical regularities, prosodic cues, and distributional patterns may provide sufficient evidence for acquiring complex grammar without innate linguistic knowledge. The debate turns on how much innate structure is required — not whether learning happens, but what the prior is.

The POS argument remains central to linguistic nativism and remains empirically contested.