Isagoge Philosophica

We know universals by abstraction, or by a certain separation from the singulars in which they exist—not a real separation, but one made by reason and consideration. Let the universals attributed to Plato be dismissed as worthless, like old wives’ tales: if they were really separated from singulars (as Aristotle either supposes or pretends that Plato supposed), they would contribute nothing either to the being of those singulars or to our knowledge of them.

This abstraction takes place when the intellect, with the senses as its ministers, gathers from singular things not the common natures themselves that exist in them, but certain species or natural likenesses by which those natures are represented without any individual difference. For each cognitive faculty in us abstracts and separates its object from the objects of other cognitive faculties by means of species received from the things themselves. For example, butter contains whiteness, sweetness, a distinctive odor, softness, and other accidents, as well as the singular substance of the butter itself. Sight abstracts and separates whiteness from sweetness and the other things present in the milk by means of the species of whiteness it receives through the eyes, although whiteness remains really joined to them. In the same way taste abstracts sweetness by means of its species, and so do the other senses, both external and internal. But because the senses are material and attached to bodily organs, they know only singulars and can abstract only certain material and sensible things from other material and sensible things. For this reason all the species they use in knowing are called sensible. The intellect, by contrast, is an immaterial power and is not attached to any bodily organ; by the nobility of its nature it can therefore perceive universals and abstract them from singulars by means of species of a higher nature, which are called intelligible.

This kind of abstraction occurs in the following way. The familiar external senses, as it were the first gatekeepers of our mind, receive and somehow draw in the species of sensible accidents belonging to things present to them. Through these species they gain intuitive, or present, awareness of those accidents. They then report to the common sense, which presides over them all and may be called partly internal and partly external, what accidents are before them. They do this by transmitting to it certain likenesses through which it can know all that each sense has perceived, compare these things with one another, and distinguish them. The common sense may be called partly internal and partly external because, although its seat and dwelling place are internal, it would make no difference to call its function external: like each of the five familiar external senses, it can know nothing privately within itself, but only when the things themselves are present.

Next, the common sense, as it were by striking the imagination—which serves the intellect most closely and is wholly an internal sense—gives it occasion to draw from the species received from the external senses other species called phantasms. Among sensible, or material, species these are of so noble a nature that they can represent things absent, past, and future, as well as many things that the other senses have not perceived: a past injury from a blow, the future benefit of food, the poison in a harmful plant, and the usefulness of a wholesome one. Prompted and guided, as it were, by such phantasms, a dog flees a stick and a sheep a wolf, while the dog follows the hunter and the sheep the shepherd. Their power in human beings is so great, because imagination is joined to intellect, that some very learned men have held that phantasms can also represent the singular material substances themselves that lie hidden beneath sensible accidents. For the same reason, they hold, imagination can compose singular things from singular things and reason from one to another.

Finally, imagination, though a single power, takes on different names and accounts from the different functions it performs. By offering phantasms to the intellect, so to speak, it supplies the matter and objects for understanding. The phantasms themselves cannot act on the intellect, since they are material and the intellect is immaterial. But the intellect is twofold: one part can act on material things to produce immaterial effects; the other can be acted upon by immaterial things. The former is usually called the agent intellect, the latter the patient, receptive, or possible intellect. Raised by the light of the agent intellect, phantasms impress intelligible species upon the possible intellect, much as colors cannot of themselves, in darkness, send their species into the eyes; but when the light of the sun or a lamp arrives and raises them by its power, they can move the eyes and impress on them their likeness, so that the eyes can see them. The agent intellect is an inward, spiritual light which in a way makes things that are universal in potency universal in act, just as bodily light makes colors that are visible in potency visible in act, as Aristotle says.

By these intelligible species, which represent universal natures without any admixture of singularity, both intellects are said to abstract universal natures from singular things. The agent intellect produces these species; the patient intellect, as if looking straight at things through them, knows universals alone. Yet when it is in a way turned and directed downward, it also understands singulars through the same species together with phantasms. We must not deny that our intellect has true and determinate perception of singular things, especially since the higher cognitive faculties must be granted every kind of knowledge attributed to the lower faculties, though in a different and more noble mode.

From this it is clear that there are two kinds of abstraction, whether we consider the abstraction performed by the sensitive powers or that performed by the intellect. One is the separate representation of an object in a species; the other is its separate apprehension. We have spoken of abstraction by the sensitive powers by way of example and as a kind of guidance, and also to show the progress of the cognitive faculties up to the first abstraction of universal natures from singulars.

How the intellect alone abstracts more universal natures from less universal ones need not concern us here. The account is the same as for abstraction of universals from singulars: a nature is first said to exist universally in the mind when it is represented by any intelligible species or perceived by a concept corresponding to it, whether the species and concepts are more or less common, and whether the species are produced with the help of phantasms or by the intellect’s operation alone.

It is in this one sense that what philosophers commonly say—that universals are made by the operation of the intellect—can be true. For whatever comes to be acquires a new actual existence, and this is of two kinds. One is real existence, which universals as such cannot have, since whatever exists in reality must exist as a singular. The other is objective existence, which the sensitive faculties cannot give them. It follows that only through the intellect’s operation do universals as such come to be and, in their own way, arise—that is, have objective existence: habitually in the intelligible species by which they are represented, and actually in the concepts by which they are apprehended.