In structuralism (binary) opposition is seen as fundamental to human thought. See Oppositional Concepts in Computational Intelligence, by H. R. Tizhoosh, Springer, 2008, Positions, by Jacques Derrida, Univ. Chicago Press, 1982, and the works of Ferdinand de Saussure. The importance and use of oppositional concepts is discussed by various authors in Tizhoosh's book. When my artificial intelligence A.s.a. H. Includes a category's (concept's) logical complement it has this form. (see my paper in Trans. Kansas Acad. of Sci., vol. 109, # 3/4, 2006, equation 3, with the printing error corrected so that it reads Ci* = 1 - Ci = 1 - In.Ini) (You only need to store Ci, you can generate Ci* from it when needed.) Similarly, when using vector categories (as Asa H does) we can consider the negation of each vector.