C-command
c-command (constituent command) is a relationship between the nodes of grammatical parse trees. It is closely associated with the phrase structure grammars of the Chomskyan tradition (Government and Binding, Minimalist Program), and may not be valid or applicable to the tree structures of other theories of syntax, such as dependency grammars. The relation of c-command has served as the basis for many explorations and explanations of phenomena of syntax. It has been taken to be the basic configurational relation underlying binding, and has played a central role in the analysis of diverse syntactic mechanisms, such as parasitic gaps and the scope of quantifiers.
Informally speaking, a node in a tree c-commands its sibling node(s) and all of its siblings' descendants; however, a node without siblings c-commands everything that its parent c-commands.
The definition of c-command is based partly on the relationship of dominance: Node N1 dominates node N2 if N1 is above N2 in the tree and one can trace a path from N1 to N2 moving only downwards in the tree (never upwards); that is, if N1 is a parent, grandparent, etc. of N2.
Based upon this definition of dominance, node A c-commands node B if and only if:
For example, according to this definition, in the tree at the right,
If node A c-commands node B, and B also c-commands A, it can be said that A symmetrically c-commands B. If A c-commands B but B does not c-command A, then A asymmetrically c-commands B. The notion of asymmetric c-command plays a major role in Richard Kayne's theory of Antisymmetry.
A number of variations of the c-command relationship have been proposed, a prominent one being m-command, which is used in defining the notion of government.
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