 As we saw above, the distinction between simple and complex objects, or (roughly) between objects and states of affairs, is fundamental to Burley’s ontology. This distinction is the objective counterpart of the linguistic distinction between simple and compound expressions (i.e., nouns vs. sentences or propositions). Thus, Burley can view states of affairs as propositions existing in re. In the prologue to his final commentary on the Categories, he claims that a mental proposition is what is signified by a spoken (or written) sentence. The mental proposition in turn signifies something else, because it is composed of concepts, which are themselves signs. As a result, the ultimate significatum of this chain must be something that is signified but does not signify, and which has the same logical structure as the mental proposition—i.e., it must be a proposition in re (fols. 17vb–18ra; see also ch. de priori, fol. 47va). Such a real proposition is an ens copulatum formed by the entity for which the subject and the predicate stand together with an identity-relation, if the proposition is affirmative, or a non-identity relation, if the proposition is negative (EP, prooem., fol. 18va; EPh, prol., fol. 66ra–b). These complex objects differ from aggregates (the significata of concrete accidental terms), which are also made up of items belonging to different categories since mere aggregates do not include the identity (or non-identity) relation, and, like simple objects, cannot be true nor false (EP, ch. de oppositione, fol. 45va). In the chapter de priori, he maintains that there are four kinds of proposition, written, spoken, mental, and real, and specifies that the mental proposition is twofold: the first, existing in the mind as in a subject (habens esse subiectivum in intellectu), is composed of acts of understanding; the second, existing in the mind as the object of the preceding complex act of understanding (habens esse obiectivum in intellectu), is what we grasp by means of the mind and compare with reality to determine the truth or falsity of a proposition. This is the semantic link between the written, spoken, and (first) mental propositions on the one hand, and the real proposition (the state of affairs) they signify on the other. It exists even if the written, spoken, and (first) mental propositions are false and nothing corresponds to them in reality (fol. 48vb). Accordingly, the proposition habens esse obiectivum in intellectu is now the sense of a sentence, and not its extension. On the other side, the new real proposition is the significatum of the sentence and its truth-maker, since those sentences that signify a complex object existing in reality are true, whereas those sentences that do not signify such a complex object, but to which only the two (simple) objects designated by the subject and predicate correspond in reality, are false.