complementarity See PHILOSOPHY OF SCIENCE,. QUANTUM MECHANIC. complementary class, the class of all things not in a given class. For example, if C is the class of all red things, then its complementary class is the class containing everything that is not red. This latter class includes even non-colored things, like numbers and the class C itself. Often, the context will determine a less inclusive complementary class. If B 0 A, then the complement of B with respect to A is A – B. For example, if A is the class of physical objects, and B is the class of red physical objects, then the complement of B with respect to A is the class of non-red physical objects. See also SET THEORY. P.Mad.