In logic, negation, also called the logical not or logical complement, is an operation that takes a proposition to another proposition "not ", standing for " is not true", written , or . It is interpreted intuitively as being true when is false, and false when is true. Negation is thus a unary logical connective. It may be applied as an operation on notions, propositions, truth values, or semantic values more generally. In classical logic, negation is normally identified with the truth function that takes truth to falsity. In intuitionistic logic, according to the Brouwer–Heyting–Kolmogorov interpretation, the negation of a proposition is the proposition whose proofs are the refutations of .

तर्क के रूप में निषेध जिसे पूरक भी कहा जाता है एक संक्रिया है जो कथन को इसके p असत्य है तब निषेध p सत्य होगा। अतः निषेध एकधारी (एकल-तर्क) तर्क संयोजक है।