a property of language where elements (like words, phrases, or clauses) can contain smaller versions of themselves — this allows infinite expansion or repetition.
4 kinds
Orthographic word 正字词
string of characters
token---tokenisation 分词
Phonological word 音位词
pronounceable units
stress/pauses
lexemes 词位
a set of grammatical words that are different froms of the same word
grammatical form 语法形式
citation form 引证形式
basic form 基础形式
criteria of chooing words: grammar
suppletion 补充变形
e.g. 不规则变型
morphemes 词素
定义:minimal unit of linguistic expression associated with a meaning