Marsilio Ficino’s Platonic Theology, Volume II

4It follows from this that an intelligible form cannot be divided into parts which are like one another. Is it perhaps cut into unlike parts, as an animal’s body is cut into bones, flesh, and sinews? Not at all. For through this form the mind knows what the substance of a thing is, as we have said, and the substance of a thing is grasped above all by definition. A definition consists of genus and difference: the definition of a human being, for example, consists of animal and rational. Animal is the genus through which a human being has something in common with other animals; rational is the difference by which a human being differs from animals devoid of reason. If there is any diversity of parts in that form, it will therefore consist chiefly in genus and difference. Let these two, if you will, be the parts of the intelligible form; and let them be extended across bodily breadth. Hear what follows. Since the parts of a body can be divided to infinity, both genus and difference will be cut without end along with them, and one definition will contain innumerable genera and innumerable differences. It will no longer be a definition at all, because if it is infinite the intellect cannot comprehend it, nor will it be bounded by its own limits. More absurdly still, we shall either repeat the same genera and differences infinitely, or by resolving genus ascend from genus to genus without end and, by dividing difference in the same way, descend from difference to difference. Such ascent and descent are impossible, because true reason at last reaches the first genera of things and their ultimate differences, beyond which it may not proceed. Substance is the supreme genus in a human being and is not resolved into any further genus. A certain power of discursive reasoning is the ultimate difference and cannot be narrowed into another difference. The error is increased above all by this: if genus and difference are present in any thing, infinitely many such constituents will exist in actuality. For whatever contributes to the essence of a thing and belongs to the natural order exists actually and truly in nature; it is not fashioned by human thought. Yet nature does not permit such a multitude to be innumerable in reality or actuality, least of all in a body. Still, an innumerable multitude would exist in a body if innumerable genera and differences were divided together with its bodily parts, for there would be just as many portions of the body itself.