- Language Acquisition Device (LAD)
- Chomsky's proposed innate mechanism that allows children to extract the grammatical rules of their native language from surrounding input. The LAD is hypothesised to contain Universal Grammar — abstract, cross-linguistic structural principles that constrain the space of possible human languages.
- Universal Grammar
- The hypothesis, central to Chomsky's linguistics, that all human languages share a set of underlying structural principles — and that these principles are part of the biological endowment of the human species rather than learned from experience.
- Critical period hypothesis
- Eric Lenneberg's proposal that language acquisition must occur within a biologically determined window (roughly from birth to puberty) during which the brain is maximally plastic. Evidence comes from second-language acquisition — native-like fluency becomes harder after puberty — and cases of extreme linguistic deprivation.
- Poverty of the stimulus
- Chomsky's argument that the linguistic input children receive is insufficient — too sparse and inconsistent — to explain the rich grammatical knowledge they ultimately acquire. This 'poverty' argues for an innate contribution to language knowledge.
- Child-Directed Speech (CDS)
- The simplified, higher-pitched, slower, more repetitive speech register (sometimes called 'motherese' or 'parentese') that adults across cultures use when addressing young children. CDS may help children segment speech into words and identify grammatical patterns.
- Language Acquisition Support System (LASS)
- Jerome Bruner's term for the social scaffolding that caregivers provide to support language development — interactive routines such as joint attention, turn-taking, and naming games that create the supportive linguistic environment Chomsky's nativist account largely ignores.
- Overextension and underextension
- Two common error patterns in early word learning. Overextension: applying a word too broadly ('dog' for all four-legged animals). Underextension: applying a word too narrowly ('cup' only for the child's own cup). Both reflect how children test and refine their mapping of words to concepts.
- Phonological development
- The gradual acquisition of the sound system of a language. Infants begin as 'universal listeners' sensitive to all phonemic contrasts, then narrow to the distinctions in their native language by 6–12 months. Most native phoneme contrasts are mastered by 4–5 years.