A third consideration further exposes the unsoundness of their thesis. They maintain that the essential attributes are the parts of the quiddity and that these parts precede the quiddity both in the intellect and in external existence; but these “parts” are nothing other than the attributes themselves. Consequently, they end up claiming that an attribute exists outside the mind prior to the very subject it qualifies—a proposition whose impossibility is evident to sound reason.

Their error arises from the following confusion: when one utters a description, that description is indeed a portion of the sentence and, in the order of mental conception and verbal expression, precedes the remainder of the statement. In the mind and on the tongue it is a segment of the composite that, according to them, constitutes the quiddity. Because they fail to distinguish between what exists in thought and what exists in concrete reality, they imagine that the real-world attributes that constitute a thing’s quiddity exist outside the mind prior to the thing itself. This is a glaring mistake to anyone who reflects on their words—although at times they will even declare the quiddity to be prior to its attributes.

Seventh aspect: Requiring the common essential attributes is a purely arbitrary convention.

To elaborate on this seventh aspect: they claim that a complete definition conveys the very reality of the thing, and they stipulate that such a definition must be composed of two elements—(1) the differentiating essential attribute and (2) the common essential attribute, namely the genus.

We ask them: Do you insist that one must conceive all the essential attributes a thing shares with other things, or not? If you do insist, then you will have to say, for example, “a body that grows, is sentient, and moves by volition,” whereas the single term “animal” neither indicates all those attributes directly nor through its differentia. If, however, you do not insist on that, then suffice yourselves with the differentiating attribute alone—such as “rational.” “Rational” points to “animal” just as “animal” points to “growing,” for “growing” is a proximate genus of “animal” common to both animals and plants. Accordingly, when you wish to define “animal” according to their procedure, you must say: “a body that grows, is sentient, and moves by volition,” just as you define “man” by saying: “a rational animal.”