In theoretical linguistics, m-command is a syntactic relation between two elements in a tree structure. It is a broader version of c-command, and like c-command, it is defined over the constituency-based trees associated with the phrase structure grammars (= constituency grammars) of the Chomskyan tradition (Government and Binding, Minimalist Program); it is therefore not applicable to the structures that other theories of syntax assume. For instance, it is not (or hardly) applicable to the dependency-based structures of dependency grammars. Aoun and Sportiche's (1983) definition of c-command in fact corresponds to what is now known as "m-command". Chomsky (1986) established the standard definition of m-command. If X and Y are two nodes in a syntactic tree, X m-commands Y if and only if:
- X does not dominate Y,
- Y does not dominate X, and
- the maximal projection of X dominates Y.
The notion of maximal projection is adopted from X-bar theory. The difference between c-command and m-command is that X m-commands everything that it c-commands, and in addition, it m-commands the element in the specifier position of the phrase that it heads. M-command is used in the formulation of the syntactic relation government.
- Aoun, Joseph; Dominique Sportiche (1983). "On the Formal Theory of Government". Linguistic Review 2: 211–236.
- Chomsky, Noam (1986). Barriers. Cambridge, MA: MIT Press.