A topic in the Open Knowledge Graph — a free, open map of 15,290 topics and the order to learn them in.
Children acquire language with remarkable speed and uniformity across cultures: cooing and babbling by 6 months, first words by 12 months, a vocabulary explosion around 18 months, and basic grammar by age 3. Nativist accounts (Chomsky's Language Acquisition Device, Universal Grammar) argue that children are innately equipped with linguistic structures. Interactionist and usage-based accounts emphasize the role of child-directed speech, social interaction, and statistical learning from input. The sensitive period for first-language acquisition means that early deprivation (as in Genie's case) results in permanent deficits, especially in grammar.
Track the milestones chronologically, then compare nativist vs. social-interactionist theories using specific phenomena (fast-mapping, overregularization errors like 'goed') as test cases for each theory.
Language is arguably the most complex cognitive skill humans acquire, yet children everywhere master it by age 4-5 with no formal instruction. Understanding how this happens requires examining both the universal developmental sequence and the theoretical disagreements about why it occurs so reliably and rapidly.
The milestones are remarkably consistent across cultures. Newborns prefer their native language's phonemic contrasts over foreign ones — evidence that language learning begins in the womb. By 6 months, infants are cooing and babbling with the rhythmic patterns of their language. By 12 months, the first words appear. Around 18 months comes the vocabulary explosion: children begin acquiring words at rates of 5-10 per day, a process called fast-mapping. And by age 3, children are producing multi-word sentences with basic grammatical structure — subject-verb-object ordering, tense marking, and question formation — despite never having been explicitly taught these rules.
The theoretical battle is over what explains this speed and universality. Nativists, following Chomsky, argue that children are biologically equipped with a Language Acquisition Device containing Universal Grammar — abstract structural principles shared by all human languages. The evidence: children acquire grammar even from impoverished, error-filled input (the "poverty of the stimulus"), make systematic errors that adults don't produce, and show strikingly similar developmental sequences across typologically different languages. Interactionists and usage-based theorists counter that statistical learning from rich input, social interaction, and child-directed speech ("motherese") are sufficient. Both sides use overregularization errors as evidence: nativists see the extraction of a grammatical rule (add -ed) as evidence of an innate rule-learning mechanism; interactionists see it as statistical generalization from the many regular verbs encountered.
The critical period evidence helps resolve one part of this debate. Genie, deprived of language until age 13, subsequently acquired vocabulary but never achieved normal syntax — permanent grammatical deficits despite years of instruction. Deaf children who receive sign language from birth acquire it normally; those who first encounter sign language in adolescence show lasting syntactic limitations. This dissociation between vocabulary (which remains acquirable throughout life) and grammar (which requires early exposure) suggests there is something special about early language learning, whether it is attributed to an innate LAD or to early-developing neural plasticity that closes around puberty.
The key takeaway is that language acquisition is not a passive process of imitation or storage. Children are active hypothesis-testers who construct grammar from patterns, produce novel sentences they have never heard, and refine their grammatical systems through feedback and exposure. Overregularization errors are not mistakes to be corrected — they are windows into a developing grammatical mind.