In this matter they set themselves against their own predecessors, engaging in a purely verbal dispute without providing any sound, intelligible distinction; for restricting the term “substance” to what they have designated is nothing more than a terminological convention.

By contrast, the earlier authorities maintained that substance is whatever is not in a subject, just as the theologians define it as everything that subsists by itself, or everything that occupies its own spatial locus, or everything in which attributes inhere, or everything that bears accidents, and the like.

As for any real, substantive difference, their claim that the existence of contingent beings is something added to their quiddity in the external world is false, and their assertion that the First Existent’s being is merely existence qualified by negations is likewise false, as has been set out in detail elsewhere.

The Science of the Ten Categories

The division of existence into “necessary” and “contingent” is specific to Ibn Sīnā and his followers. Aristotle and the earlier philosophers, however, divided existence only into substance and accident, and for them the contingent is nothing but what is newly originated—on this point all rational people are agreed. This discipline is the study of the ten categories, which they call the Categories.

Proofs of the Invalidity of Their Claim Concerning Demonstration

Our purpose here is to discuss demonstration (burhān). We say:

Although various groups have been misled by their discourse, it is merely ornate rhetoric containing so much falsehood that a full exposition would be lengthy. We shall therefore point out only some of its flaws, as follows:

First Aspect

Demonstration does not yield knowledge of any existent thing.

To begin: if demonstration furnishes knowledge only of universals, and universals obtain solely in the mind, not in external reality—while outside the mind there is nothing but particular, concrete entities that remain unknown—