OPPOSITION, SQUARE OF

in traditional logic, a diagram exhibiting four forms of a categorical proposition (q.v.), or statement, with the same subject and predicate, together with their pairwise relationships: in which A, E, I, and O are of the forms Every S is P, No S is P, Some S is P, and Some S is not P. As shown on the square, Every swan is white is the contrary of No swan is white and the contradictory of Some swans are not white. Conclusions drawn from one of these forms to another (as in subalternation) are said to be obtained by immediate inference.