1 The contradiction, or denial, or reversal of something, or the act or process of contradicting.
2 In psychoanalysis, a process whereby one continues to defend oneself against a formerly repressed wish, thought, or feeling that has come to consciousness by disavowing or disowning it, as when a patient says during therapy ‘You might expect me to have felt angry with him, but I never felt any anger’. Sigmund Freud (1856–1939) expounded his theory in an article entitled ‘Negation’ in 1925, where he asserted somewhat cryptically: ‘Only one consequence of the process of negation is undone—the fact, namely, of the ideational content of what is repressed not reaching consciousness. The outcome of this is a kind of intellectual acceptance of the repressed, while at the same time what is essential to the repression persists’ (Standard Edition, XIX, pp. 235–9, at pp. 235–6). Some psychoanalysts consider it as a defence mechanism. Also called disavowal.
3 In logic, the operator that reverses the meaning of a proposition p, or the resulting proposition not-p that is true precisely when p is false and vice versa.