The theory I'll defend in this dissertation is that propositions (the primary truth-bearers, contents of declarative sentences, and objects of attitudes) are token mental representations. 1 A mentalist semantics is one which analyzes representational properties of linguistic expressions in terms of the representational properties of mental states (Speaks, 2019, section 3.1). 2 Let "s" pick out an arbitrary, declarative sentence of some language (it doesn't matter which one). The view I'm defending is that, for s to be meaningful-i.e. for s to have content, and to (thereby) represent things as being a certain way-is for s to express a proposition, which is a token mental representation. This view offers an analysis of the meaningfulness of s, and the analysis makes reference to a mental representation. Moreover, suppose s represents things as being such that Cicero is an orator; the view I'm defending is that, for s to represent things as being such that Cicero is an orator is for s to express a proposition, which is a token mental representation of things being such that Cicero is an orator. This view offers an analysis of the representational properties of a linguistic expression in terms of the representational properties of a mental state. Hence, the view I'm defending is a mentalist one.