Note 245 — Chapter VIII

This point is put somewhat tentatively in a passage in Jevons’s Principles of Science (chapter 6, § 5) where he remarks: “If A were identical with ‘B or not-B,’ its negative not-A would be non-existent. This result would generally be an absurd one, and I see much reason to think that in a strictly logical point of view it would always be absurd. In all probability we ought to assume as a fundamental logical axiom that every term has its negative in thought. We cannot think at all without separating what we think about from other things, and these things necessarily form the negative notion. If so, it follows that any term of the form ‘B or not-B’ is just as self-contradictory as one of the form ‘B and not-B’.”