 On Burley’s later view, macro-objects (i.e., what is signified by a proper name or definite description such as Socrates or some particular horse) are basic components of the world. They are aggregates made up of primary substances together with a host of substantial and accidental forms, both universal and singular, existing in them and through them. Primary substances and substantial and accidental forms are simple objects or categorial items, each possessing a unique, well-defined nature. These simple objects belong to one of ten main types or categories, each really distinct from the others. Although they are simple, some of these components are in a sense composite because they are reducible to something  else—for example, primary substance is composed of a particular form and matter (EP, ch. de substantia, fol. 22ra). Primary substance differs from the other components of a macro-object because of its peculiar mode of being as an autonomous and independently existing object—in contrast to the other categorial items, which necessarily presuppose it for their existence (EP, ch. de substantia, fol. 22ra–b). Primary substances are therefore substrates of existence and predication in relation to everything else. The distinction between substantial and accidental forms derives from their different relations to primary substances, which instantiate substantial forms (which in turn, qua instantiated, are secondary substances), so that such universal forms disclose the natures of particular substances. By contrast, those forms that simply affect primary substances without being actually joined to their natures are accidental forms. In Burley’s words, the forms in relation to which particular substances are the supposita are substantial forms (or secondary substances), whereas those forms in relation to which particular substances are the subiecta are accidental forms (TdU, pp. 58–59). As a result, the macro-object is not simply a primary substance but an orderly collection of categorial items, so that primary substance, even though it is the most important element, does not contain the whole being of the macro-object.