 Because each thought has a determinate subject-matter, it makes no sense to talk about the “reinterpretation” of thoughts. The kind of reinterpretation that Hilbert engages in, i.e., of assigning different meanings to specific words, is something that can apply only to sentences, from the Fregean point of view. Accordingly, the first difficulty Frege notes with Hilbert’s approach is that it is not clear what Hilbert means by “axioms:” if he means the kinds of things for which issues of consistency and independence can arise, then he must be talking about thoughts, while if he means the kinds of things that are susceptible of multiple interpretations, then he must be talking about sentences.