Lexeme

One form, the lemma (or citation form), is chosen by convention as the canonical form of a lexeme. The lemma is the form used in dictionaries as an entry's headword. Other forms of a lexeme are often listed later in the entry if they are uncommon or irregularly inflected.

Description

The notion of the lexeme is central to morphology, the basis for defining other concepts in that field. For example, the difference between inflection and derivation can be stated in terms of lexemes:

• Inflectional rules relate a lexeme to its forms.
• Derivational rules relate a lexeme to another lexeme.

A lexeme belongs to a particular syntactic category, has a certain meaning (semantic value), and in inflecting languages, has a corresponding inflectional paradigm. That is, a lexeme in many languages will have many different forms. For example, the lexeme RUN has a present third person singular form runs, a present non-third-person singular form run (which also functions as the past participle and non-finite form), a past form ran, and a present participle running. (It does not include runner, runners, runnable etc.) The use of the forms of a lexeme is governed by rules of grammar. In the case of English verbs such as RUN, they include subject–verb agreement and compound tense rules, which determine the form of a verb that can be used in a given sentence.

In many formal theories of language, lexemes have subcategorization frames to account for the number and types of complements. They occur within sentences and other syntactic structures.