Language acquisition — the process by which children learn their native language — is one of the most impressive cognitive achievements of early childhood. By age 5, children have mastered the phonology, vocabulary (several thousand words), grammar (complex syntax and morphology), and pragmatics of their language, despite receiving no formal instruction. How this occurs — the relative contributions of innate language capacity, statistical learning, social interaction, and environmental input — remains one of the most debated questions in cognitive science.
Milestones
Preference for native language, categorical perception of speech sounds, babbling begins
Perceptual narrowing to native phonemes, canonical babbling, first words around 12 months
Vocabulary explosion (50-200 words), two-word combinations emerge
Rapid grammar development, overregularization errors, 10,000+ words by age 5
Nativist vs. Usage-Based Accounts
Chomsky's nativist position holds that children are born with an innate language faculty — Universal Grammar — that constrains the possible grammars children can hypothesize. Usage-based (constructivist) accounts, championed by Michael Tomasello, propose that children learn language through general cognitive abilities (pattern finding, analogy, statistical learning) applied to the linguistic input they receive. The debate continues, with current evidence suggesting contributions from both domain-specific and domain-general mechanisms.
Chomsky's poverty of the stimulus argument holds that the linguistic input children receive is insufficient to determine the grammar of their language without innate constraints. Children never hear certain sentences but know they are grammatical or ungrammatical. Critics counter that the input may be richer than claimed and that statistical learning mechanisms can extract grammatical regularities from distributional patterns in speech. This debate remains central to language acquisition theory.