 These differences mean that in Burley’s system a distinction can be drawn between the intension and the extension of an expression. We usually think of the intension of a term as the set of essential properties that determines the applicability of the term itself, and its extension as the set of things to which it is properly applied. From an epistemological point of view, this makes our ability to pick out the extension of a term dependent on our knowledge of its intension. If we treat common natures and particular things as the intension and extension of terms, respectively, we come very close to Burley’s account, with the possible exception of the ontological status of intensions (if we are ‘nominalists’), since Burley regards both common natures and particular things as entities in the world. Hence Burley distinguishes what a term signifies (id quod terminus significat) from what it denotes (id quod terminus denotat), which is reflected in the distinction between simple and personal supposition. According to him, the sentence ‘the father and the son are simultaneous by nature’ is true if the two subjects have simple supposition and so refer to their significata, i.e., the two aggregates compounded by substance and accidental form. On the other hand, if we assume that the subjects have personal supposition and so refer only to the two substances, ‘father’ and ‘son’, then the sentence is false (TsP, ch. de relatione, ed. Conti, pp. 71–72; EP, ch. de relatione, fol. 37ra–b). In the De suppositionibus and De puritate the same idea is expressed by the definition of formal supposition as the supposition that a term has when it supposits for its significatum or for the singular objects that instantiate it. In the first case, we properly speak of simple supposition, and in the second, we speak of personal supposition (De Sup., pp. 35–36, De puritate, pp. 7–8).