Abstract
Sense perceptions can serve as materials for further mental operations. The imagination can use past and present ones by abstracting and combining them in new ways. In this way there arises awareness of individual movements and substances. Experience comes about when the animal has an image generalized from these individuals, so as to have a proto-universal with many accidental features and without a theoretical account. The intellect in turn can operate on these materials so as to abstract universal concepts, separate out their accidental features, and arrive at their definitions. The intellect can then operate recursively on those concepts so as to produce even more general concepts. Thinking and perceiving have the same structure but operate on different materials, produce different content, and differ in their dependence on the organism having those abilities.The intellect is the ability of making the jump from the individual to the universal. It is infallible at what it does: apprehending universal concepts by direct intuition, but it can err in its judgements about those concepts. The universals exist in re, in the individual substances , but are there indistinctly and not separately.A science like physics works by synthesis , adding motion to perceptible substance. A science like mathematics works by abstraction, eliminating the substance and keeping only accidents like shapes, now treated as subjects in their own right. Aristotle calls these mathematical objects the ultimate abstractions. As they have a relational structure, they cannot exist in their own right.