The word is is terribly ambiguous, and great care is necessary in order not to confound its various meanings. We have (1) the sense in which it asserts Being, as in “A is”; (2) the sense of identity; (3) the sense of predication, in “A is human”; (4) the sense of “A is a-man” ... which is very like identity.2 In addition to these there are less common uses... where a relation of assertions is meant ... which ... gives rise to formal implication.