'Not / But, or the "not…but" element, is an acting technique that forms part of the Brechtian approach to performance. In its simplest form, fixing the not/but element involves the actor preceding each thought that is expressed by their character in the dialogue or each action performed by their character in the scene with its dialectical opposite. Rather than portraying a thought or action as "naturally" arising from the given circumstances of the scene or "inevitably" following from them, this technique underlines the aspect of decision in the thought or action. "He didn't say 'come in' but 'keep moving'", Brecht offers by way of example; "He was not pleased but amazed":

They include an expectation which is justified by experience but, in the event, disappointed. One might have thought that ... but one oughtn't to have thought it. There was not just one possibility but two; both are introduced, then the second one is defamiliarized, then the first as well.

"Not" is the general declarative form of "no", indicating a negation of a related statement which it usually precedes; see yes and no.

... Not! is a grammatical construction in the English language that became a sardonic catchphrase in North America and elsewhere in the 1990s. A declarative statement is made, followed by a pause and then an emphatic "not!" is postfixed. The result is a negation of the original declarative statement.