irrelevant conclusion, fallacy of See INFORMAL FAL-. LAC. is, third person singular form of the verb ‘be’, with at least three fundamental senses that philosophers distinguish according to the resources required for a proper logical representation. The ‘is’ of existence (There is a unicorn in the garden: Dx (Ux8Gx)) uses the existential quantifier. The ‘is’ of identity (Hesperus is Phosphorus: j % k) employs the predicate of identity. The ‘is’ of predication (Samson is strong: Sj) merely juxtaposes predicate symbol and proper name. Some controversy attends the first sense. Some (notably Meinong) maintain that ‘is’ applies more broadly than ‘exists,’ the former producing truths when combined with ‘deer’ and ‘unicorn’ and the latter producing truths when combined with ‘deer’ but not ‘unicorn’. Others (like Aquinas) take ‘being’ (esse) to denote some special activity that every existing object necessarily performs, which would seem to imply that with ‘is’ they attribute more to an object than we do with ‘exists’. Other issues arise in connection with the second sense. Does Hesperus is Phosphorus, for example, attribute anything more to the heavenly body than its identity with itself? Consideration of such a question led Frege to conclude that names (and other meaningful expressions) of ordinary language have a ‘sense’ or ‘mode of presenting’ the object to which they refer that representations within our standard, extensional logical systems fail to expose. The distinction between the ‘is’ of identity and the ‘is’ of predication parallels Frege’s distinction between object and concept: words signifying objects stand to the right of the ‘is’ of identity and those signifying concepts stand to the right of the ‘is’ of predication. Although it seems remarkable that so many deep and difficult philosophical concepts should link to a single short and commonplace word, we should perhaps not read too much into that observation. Some languages divide the various roles played by English’s compact copula among several constructions, and others use the corresponding word for other purposes. See also EXISTENTIAL IMPORT, IDENTITY, QUALITIE. S.T.K.