Why did Noam Chomsky criticize behaviourist explanations of language?

Noam Chomsky criticized behaviourist explanations of language because he argued that language cannot be adequately explained as a collection of behaviours learned solely through reinforcement or conditioning.12

While behaviourists viewed language learning as a response to external stimuli, Chomsky highlighted that humans possess the unique ability to understand and produce an infinite number of sentences they have never previously encountered. This "creative" aspect of language use suggested to Chomsky that language depends on internal mental systems for representing and applying grammatical rules, rather than being a simple result of environmental input.12

Furthermore, Chomsky proposed the "poverty of the stimulus" argument, noting that children acquire complex linguistic competence with remarkable speed and facility despite receiving limited or incomplete evidence. He concluded that humans must be born with an innate Universal Grammar—a set of formal principles that allow the mind to construct a grammar based on the linguistic data to which a child is exposed. This shift in perspective was a central component of the cognitive revolution, moving scientific focus toward internal mental processes.3452