Variable
（1）变形词
（2）变项
（3）变项
(1) A term used in the grammatical classification of words to refer to one of two postulated major word-classes in language, the other being invariable. Variable words are said to be those which express grammatical relationships through a change of form, e.g. boy / boys, walk / walking, nice / nicer. Invariable (or invariant) words are unchanging, whatever their distribution, e.g. in, on, and.
(2) The term has been introduced into sociolinguistics by the American linguist William Labov (b.1927) to refer to the units in a language which are most subject to social or stylistic variation, and thus most susceptible to change in the long term. Sets of phonological, grammatical and lexical variables are described quantitatively with reference to such factors as social class, age and sex, and the results of this co-variation are stated in the form of variable rules. Variable rules are generative rules which have been modified so as to specify the socio-regional conditions under which they apply. The notion has been developed primarily in relation to hypotheses concerning the relationship between social variation and linguistic evolution.
(3) The term is also widely used in grammar and semantics in its general sense of a symbol which may assume any of a set of values. For example, a category variable (e.g. X) stands for any level of bar projection of X (e.g. Xn stands for X0̍, X̍, X̎). Pro-forms are often analysed semantically as variables, especially when they are bound by quantificational antecedents. In government-binding theory, the term refers to an A-bar-bound trace.
（1）语法有时假设语言的词分为两大类，即变形词和不变形词。变形词是通过改变形式表达语法关系的词，如boy / boys“男孩”（单数/复数），walk / walking“走”（原形/-ing形式），nice / nicer“好”（原级/比较级）。不变形词不管分布如何都不改变形式，如in“在…里”，on“在…上”，and“和”。
（2）美国语言学家威廉·拉波夫（生于1927）引入社会语言学的术语，指语言中最容易产生社会或风格变异，因而从长期看最容易发生演变的那些单位。音系的、词汇的、语法的各组变项可参照社会等级、年龄和性别等因素作定量描写，然后用变项规则的形式说明这种协同变异的结果。变项规则是经过修改的生成规则，因而能指明其使适用的社会—地域条件。这个概念的提出主要与社会变异与语言演化之间有联系的假说有关。
（3）按一般涵义广泛用于语法和语义学，指一个数量项在一组值中可取任何一个值。例如，一个范畴变项（例如X）代表任何一个词层面的主要范畴（如N，P，Adj）；一个杠变项在X-杠句法中代表X的任何一个层面的杠投射（如Xn代表X0，X̍，X̎）。在管辖与约束理论中变项是约束理论的一个重要组成部分。