negation the logical operation on propositions that is indicated, e.g., by the prefatory clause ‘It is not the case tha. . .’. Negation is standardly distinguished sharply from the operation on predicates that is called complementation and that is indicated by the prefix ‘non-‘. Because negation can also be indicated by the adverb ‘not’, a distinction is often drawn between external negation, which is indicated by attaching the prefatory ‘It is not the case tha. . .’ to an assertion, and internal negation, which is indicated by inserting the adverb ‘not’ (along with, perhaps, grammatically necessary words like ‘do’ or ‘does’) into the assertion in such a way as to indicate that the adverb ‘not’ modifies the verb. In a number of cases, the question arises as to whether external and internal negation yield logically equivalent results. For example, ‘It is not the case that Santa Claus exists’ would seem obviously to be true, whereas ‘Santa Claus does not exist’ seems to some philosophers to presuppose what it denies, on the ground that nothing could be truly asserted of Santa Claus unless he existed. See also DOUBLE NEGATION, TRUTH TABL. R.W.B.