 Propositions and propositional functions are unlike definite descriptions and classes in that there are no explicit definitions of them in PM. It is unclear what it means to say that a symbol for a proposition, such as a variable \(p\) or \(q\), has “no meaning in isolation”, and that, however, the meaning can be given “in context”, as it would seem that there no definition is possible, it would seem, in a logic in which propositions and propositional functions appear as primitive notions in the statement of the axioms and definitions of logic.