According to Frege, the sentence ‘Socrates is mortal’ can be analysed into the proper name ‘Socrates’ combined with the one-place predicate ‘ξ is mortal’. It is uncontroversial that the two items are governed by different grammatical rules of combination. But Frege also introduced semantic distinctions between them that have been contended ever since. He made them refer to different types of thing. The proper name refers to an object, while the predicate refers to a concept, which he proceeded to identify with a function from objects to truth-values, e.g. from Socrates to truth. His distinction between objects and functions is exclusive: nothing can be both.