Law of noncontradiction


The law of non-contradiction is a rule of logic. It states that if something is true, then the opposite of it is false. For example, if an animal is a cat, the same animal cannot be not a cat. Or, stated in logic, if +p, then not -p, +p cannot be -p at the same time and in the same sense. The law was stated as a principle of mathematical logic by Russell and Whitehead in Principia Mathematica.[1]

Ravi Zacharias has said most eastern philosophies reject the law of noncontradiction.[2] The law of non-contradiction is found in ancient Indian logic as a rule in the Shrauta Sutras, the writing of Pāṇini,[3] and the Brahma Sutras attributed to Vyasa. It was later elaborated on by medieval commentators such as Madhvacharya.[4] The idea of noncontradiction is rejected in some strands of Buddhism.


  1. Alfred North Whitehead, Bertrand Russell (1910), Principia Mathematica, Cambridge, pp. 116–117
  2. Zacharias, Ravi The Real Face of Atheism page 176
  3. Frits Staal (1988), Universals: Studies in Indian Logic and Linguistics, Chicago, pp. 109–28 (cf. Bull, Malcolm (1999), Seeing Things Hidden, Verso, p. 53, ISBN 1-85984-263-1)
  4. Dasgupta, Surendranath (1991), A History of Indian Philosophy, Motilal Banarsidass, p. 110, ISBN 81-208-0415-5

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