 A part of speech (pars orationis) is the result of the hylomorphic composition of a word and a mode of signifying. The mode of signifying, in turn, is derived from some of the modes of being a thing may have (QPm; QPm-1980: 164). For instance, a ‘walk’ has the mode of signifying of a qualified substance, because it indicates the action of walking as a qualified substance (QPm; QPm-1980: 192–193). This mode of signifying directly results from a particular mode of understanding (modus intelligendi) the action of walking, namely from understanding it as a qualified substance. Generally speaking, then, the modes of signifying are taken from their corresponding modes of understanding; and the modes of understanding, in turn, are taken from the modes of being of things. This is, in fact, the fundamental tenet of the modistic grammar to which Brito adheres: the modes of signifying follow from the modes of understanding things, which in turn follow from the modes of being of things. Note, however, that a walk is in itself an action and not a substance. But this is not a problem for grammar’s scientific status because a grammatical item takes its mode of signifying from the possible modes of being of things and not necessarily from the actual modes of being of a word’s significate (QPm; QPm-1980: 164). Consequently, every mode of signifying is ultimately grounded in a real mode of being, making the science of grammar grounded in something real. 