In linguistics, antisymmetry is a syntactic theory presented in Richard S. Kayne's 1994 monograph The Antisymmetry of Syntax. It asserts that grammatical hierarchies in natural language follow a universal order, namely specifier-head-complement branching order. The theory is built on the foundation of X-bar theory. Kayne hypothesizes that all phrases whose surface order is not specifier-head-complement have undergone syntactic movements that disrupt this underlying order. Others have posited specifier-complement-head as the basic word order.