According to Frege, the sentence 'Socrates is mortal' can be analysed into the proper name 'Socrates' combined with the one-place predicate '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. He marked the difference by saying that an object is complete or saturated, whereas a function is incomplete or unsaturated. Proper names and predicates also differ in the way in which they refer to their referents. Frege uses 'refers to' as an umbrella term covering different relations, since his principle for individuating them dictates that the reference relation holding between a proper name and an object is of a different type from the relation holding between a predicate and a concept. He made further semantic distinctions between proper names and predicates at the intermediate level of sense, but discussion of them will not be necessary, except in §2.4.

These syntactic and semantic contrasts between proper names and predicates are relational in character. My question is whether proper names and predicates also differ in their intrinsic nature. Are they different sorts of thing, as different perhaps as the corresponding objects and concepts?