from stumbling in its reflections; for when the scale itself is tilted and not level, the one who weighs will unavoidably misjudge the weight. I have dealt with this error at length elsewhere.

One of the easiest ways to see the flaw is to say, “The human being that exists outside the mind is composed of two accidents or of two substances.” When you speak of “animality and rationality,” or of “animal and rational,” do you mean by these two accidents—attributes that inhere in the human being—or two substances, entities that subsist on their own?

If you say they are accidents, the invalidity of your claim is obvious: the human being that exists is a self-subsisting substance, and substances are not composed of accidents, nor are accidents prior to them or their underlying matter. Rather, accidents inhere in a substance, depend on it, and reside within it; in your terminology, the substance is their subject, and the subject is that locus which, in its own existence, has no need of what inheres in it. Accordingly, if the human being, in your view, stands independent of his accidents, it is impossible for those accidents to be his matter or his constitutive parts, or for him to be composed of them.

If, however, you maintain that “animality and rationality”—or “animal and rational”—are two independent substances and that the human being is compounded of them, this is patently false. We know that the human being is the rational animal: a sentient, growing body that moves by volition and speaks; and that the horse is the whinnying animal: a sentient, growing body that moves by volition and neighs. Within the human being there is no separate substance that is “animal,” another that is “rational,” another that is “body,” still another that is “sentient,” “growing,” or “self-moving.”