Even if we supposed that the existence shared by the necessary and the contingent being existed externally in both, and that the shared animal nature was itself identically present in rational and non-rational animals, one would still be distinguished from the other by its own particular existence. This is just as a human being is distinguished by an animal nature peculiar to him, and as blackness and whiteness, though sharing the designation “color,” are distinguished from one another by their particular colors.

These misguided people make one thing into two and two things into one. They identify one attribute with another and identify the attribute with that which possesses it. Thus they make two things into one, as when they say that knowledge is power and will, and that knowledge is the knower. They also make one thing into two, as when they treat a particular entity—this human being—as several substances: a human being, an animal, a rational being, a rational being, a sentient being, and a being that moves voluntarily. They regard each of these substances as distinct from the others, although it is known that this is one substance possessing several attributes.

Likewise, they distinguish between matter and form and make them two self-subsisting intelligible substances. Yet what reason apprehends is simply attributes inhering in the things that possess them, and accidents inhering in substances. This is the case with a form imparted by craftsmanship, such as the form of a ring, a dirham, a bed, or a cloth: it is an accident inhering in a substance, namely silver, wood, or yarn. Connection and separation likewise inhere in a substrate, namely a body.

In the same way, they make the mental form exist externally, as in their account of abstract entities separate from matter. Yet they have nothing that establishes anything as separate from matter except the rational soul when it leaves the body at death. Abstractions are the universals that the soul abstracts from individuated particulars. Thus it all comes down to the soul and what inheres in it. They identify the giver of existence in external reality with what exists in the mind, just as they identify necessary existence with absolute existence.