Since Burley conceives of primary substances as the ultimate substrates of existence and subjects of predication in relation to anything else (EP, ch. de substantia, fols. 24va-b, and 25va), the only way to demonstrate the reality of beings in other categories is to treat them as forms and attributes of substances.
Action is an attribute of substance, for Leibniz defines substance as "a being capable of action" (GP vi, 598).
Descartes takes a similar view of time, which is judged to be a generalized abstraction from the "durations" of particular bodies (where duration is an attribute of substance; Pr II 56 57; see Gorham 2007 for more on time in Descartes).
The highest form of knowledge consists of an intellectual intuition of things in their existence as modes and attributes of eternal substance, or God; this is what it means to see the world from the aspect of eternity.
Modes are properties that exist only as modifications of the essential (principal) and the general attributes of a substance.
What makes the principal attribute, principal, so to speak, is that all attributes of a substance must be thought of through the principal attribute.
However, he does not agree that they are attributes of created substances, since he rejects the possibility of created substances altogether (1P6Cor., 1P8Schol1, 1P14).
She holds that though we can know some of the attributes of these substances, we cannot know their true natures (Astell 2002, 173).
This simply follows from the fact that freedom is a dual power and from the fact that "Powers belong only to Agents, and are Attributes only of Substances" (E1-5 II.xxi.16: 241).
