 The standard semantic clause for negation has it that \(\neg A\) is true if and only if \(A\) is not true. So there could not be worlds at which both or neither of \(A\) and \(\neg A\) are true, unless we revise the semantics of negation. Stalnaker (1996) argues that negation is such a basic operator, whose semantics is ‘learned in a first logic class’ that it had better be left alone. 