lexicon

Meaning: In the psychology of language, the lexicon is a person's mental store of words and morphemes, along with what each one means, how it sounds, and how it is used. Building it is central to language development. Children typically begin with a small set of words and then expand their vocabulary rapidly, and comprehension generally runs ahead of production.

On the MCAT: Expect the lexicon to appear in questions about the components of language. The usual pairings are phonology (sound patterns), morphology (word parts such as morphemes), semantics (meaning), syntax (rules for ordering words), and pragmatics (using language in social context). A passage might describe a child's growing vocabulary or a patient who struggles to find words, and ask which component is involved. Vocabulary size and word retrieval point to the lexicon and semantics. Word order and sentence structure point to syntax. The term can also connect to theories of language acquisition, such as the nativist view (an innate capacity for language, as proposed by Chomsky), the learning/behaviorist view (reinforcement and imitation), and the interactionist view (biology plus social interaction). All of these theories have to explain how the lexicon is acquired.

Common confusion: Students sometimes treat the lexicon as the whole of language knowledge. It holds the words only. Knowing many words does not mean knowing the grammar rules for combining them. Those rules belong to syntax, and a sentence can use real words and still be ungrammatical.