Concept
In generative grammar and related frameworks, a node in a parse tree c-commands its sister node and all of its sister's descendants. In these frameworks, c-command plays a central role in defining and constraining operations such as syntactic movement, binding, and scope. Tanya Reinhart introduced c-command in 1976 as a key component of her theory of anaphora. The term is short for "constituent command". Common terms to represent the relationships between nodes are below (refer to the tree on the right): M is a parent or mother to A and B. A and B are children or daughters of M. A and B are sisters. M is a grandparent to C and D. The standard 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. For a node (N1) to c-command another node (N2) the parent of N1 must establish dominance over N2. Based upon this definition of dominance, node N1 c-commands node N2 if and only if: Node N1 does not dominate N2, N2 does not dominate N1, and The first (i.e. lowest) branching node that dominates N1 also dominates N2. For example, according to the standard definition, in the tree at the right, M does not c-command any node because it dominates all other nodes. A c-commands B, C, D, E, F, and G. B c-commands A. C c-commands D, F, and G. D c-commands C and E. E does not c-command any node because it does not have a sister node or any daughter nodes. F c-commands G. G c-commands F. 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 S. Kayne's theory of Antisymmetry. A simplification of the standard definition on c-command is as follows: A node A c-commands a node B iff Neither A nor B dominates the other, and Every branching node dominating A also dominates B As such, we get sentences like: (1) [John] likes [her] Where [node A] John c-commands [node B].