 The most fundamental notion in Adams’ account is that of a proposition, by which he means an abstract entity that is expressed by a declarative sentence and which can be either true or false, depending on how the world is. (As in the discussion of Prior, we will continue to use logical formulas ambiguously, sometimes as names for themselves, sometimes as names for the propositions they are meant to express, trusting context to disambiguate.) Particularly important for Adams’ account is the notion of a singular proposition  introduced in §4.3,  i.e., a proposition that “involves or refers to an individual directly” (1981: 6). Crucially, as a strict actualist, Adams follows Prior in holding that a singular proposition is ontologically dependent on the individuals it is about—the “subjects” of the proposition—and, hence, that, necessarily, a singular proposition exists if and only if all of its subjects exist. Beyond this, Adams does not provide a rigorous theory of propositions but, rather, takes the notion to be sufficiently well-understood for his purposes.