 Gottlob Frege famously distinguished between an expression's reference and its sense. (The classic source is Frege 1892/1948. The distinction was first introduced a year earlier in (1891). It is commonly thought, and Frege asserts as much, that the sense-reference distinction was not present in (1879/1967). But this early work does contain a seeming anticipation of the distinction, as well as the same argument from the opening paragraphs of (1892/1948) against the metalinguistic solution promoted in (1879/1967), which is extremely puzzling. We don't try to resolve the interpretative issues here.) We focus on proper names, although Frege maintained that the sense-reference distinction applied to all expressions, including sentences, where the reference of a sentence is a truth value and its sense a thought. The reference of the name ‘Mark Twain’ is the man Mark Twain himself, while its sense is a mode of presentation or way of thinking of that object.