Thus, when it is said that what I apprehend inwardly also exists outside myself, the statement is correct; for the natural universal, taken absolutely and without qualification, corresponds to the concrete particulars that are found in the external world.

Hence, when one says that the term “human being” applies to this individual and that individual alike, the claim is sound. The situation differs with the conceptual universal, for it is predicated only on condition of its very universality, and that exists solely in the mind, not in external reality. It therefore fails to correspond to what is outside; it belongs instead to the realm of mental constructions—just as the mind can posit things that are impossible in the real world, such as combining opposites or abolishing both opposites at once.

If, then, one imagines a thing that is both existent and non-existent, or neither existent nor non-existent, such imagining occurs only in the intellect and never in the external domain. Those who thought that this sort of universal exists outside—either side by side with particular entities or apart from them—have erred, just as other philosophers before them erred. These philosophers are often mistaken, supposing that what exists only in thought is likewise found in the world. A prime example is the error of Pythagoras and his followers concerning absolute, abstract numbers: they believed that such numbers subsist externally, independent of the things that are counted or measured. Another is the error of Plato and his school regarding universal natures, such as the universal “man” and the universal “animal,” for they imagined these to exist outside the mind as eternal, everlasting universals, abstracted from concrete particulars. They said the same about time, space, and matter, supposing that there is in the external realm an eternal, everlasting intellectual substance distinct from bodies and their attributes, as well as an eternal archetypal substance separate from bodies, their motions, and the magnitudes of those motions. They likewise affirmed a purely intellectual matter stripped of every form, identifying it as the prime matter upheld in their doctrine.