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Language acquisition follows a remarkably consistent sequence across cultures: cooing (1–2 months), canonical babbling with consonant-vowel combinations (6–8 months), first words around 12 months, vocabulary explosion at 18–24 months, two-word combinations, and near-complete basic grammar by age 5. Chomsky's nativist theory proposes a language acquisition device — innate grammatical knowledge — explaining children's ability to generalize grammatical rules beyond explicit instruction. The interactionist view holds that biological readiness interacts with rich linguistic input: child-directed speech (motherese), joint attention, and contingent responding by caregivers significantly accelerate acquisition. A sensitive period for language acquisition exists, particularly for phonological discrimination and syntactic acquisition; exposure to language after this window produces less complete outcomes.
Track the emergence of language milestones using audio or video examples; analyze transcripts for telegraphic speech, overextension, and overregularization errors (e.g., 'goed', 'mouses') that reveal rule application. Compare bilingual acquisition to clarify what is universal vs. input-dependent.
From the first weeks of life, infants are already processing language. Newborns prefer the prosodic pattern of their native language over foreign languages — a preference established in utero from the mother's speech. By 6–8 months, canonical babbling begins: strings of consonant-vowel syllables like "bababa" or "mamama." At around 12 months, a first word emerges. Between 18 and 24 months, the vocabulary explosion hits — children may acquire several new words per day. Two-word combinations ("more milk," "daddy go") appear around 18–24 months, and by age 5 children have mastered most of the grammatical structures of their native language. This sequence is remarkably consistent across cultures and languages.
Two major theoretical traditions explain how this happens. The *nativist* view, associated with Noam Chomsky, holds that children are born with a language acquisition device — an innate grammatical blueprint that provides universal constraints on possible language structures. This explains why children rapidly master grammar despite hearing only incomplete and error-filled input (the poverty of the stimulus argument). The *interactionist* view counters that biological readiness is necessary but not sufficient: the quality and quantity of linguistic input matters enormously. Child-directed speech (higher pitch, exaggerated intonation, simplified vocabulary) and contingent responding — adults following the child's gaze and commenting on what the child attends to — measurably accelerate acquisition.
Overregularization errors are one of the most theoretically important phenomena in language acquisition. A child who first says "went" (correct, presumably imitated) but later says "goed" (incorrect overgeneralization) is revealing that they have internalized the past-tense rule. This U-shaped developmental curve — correct, then incorrect, then correct again — is strong evidence that children are not simply imitating but are actively constructing grammatical rules and then learning their exceptions.
The sensitive period for language acquisition reflects the fact that neural plasticity for language is highest early in life and declines after puberty. Phonological discrimination is particularly time-sensitive: infants can distinguish phoneme contrasts from all languages at birth, but by 12 months they have narrowed their sensitivity to the contrasts used in their native language. This is why native-like accents in a second language are nearly impossible to acquire after adolescence. Syntax and morphology have a somewhat longer window, but also show sensitivity effects.
Understanding language acquisition matters well beyond child development: it informs early childhood education, explains why early intervention for hearing loss is urgent, provides evidence on the bilingualism debate, and grounds theories of human cognition more broadly. The speed at which children acquire language — without formal instruction, from imperfect input, generalizing rules they were never explicitly taught — remains one of the most remarkable cognitive achievements in biology.