or fail to correspond.
Here, however, they have differentiated between attributes that are in fact alike, counting some of them as essential, lying within the very reality of the thing, and others as accidental, external, yet inseparable from that reality.
Second point: People’s knowledge of whether an attribute necessarily belongs to its subject varies from person to person. Someone may hesitate over a given thing—unsure whether it is an animal, or even whether it is a color—until he learns the truth, just as one may doubt whether a particular number is even until he verifies it by means of a middle term. In that event there is no difference between what they have labeled “essential” and what they have called “accidental yet necessary to the essence,” and that is precisely what needed to be shown.
As for the distinction they draw between “what is necessary to the quiddity” and “what merely accompanies its existence,” the gist is that the mind can posit a quiddity devoid of the first kind of attribute, unlike the second. Thus one may imagine a horse without a shadow, or a horse that has never been created; indeed, one can conceive of a Negro who is not black, a crow that is not black, and the like.
Now, if what is in the mind is taken to be the reality itself, and by “reality” one means the reality present in the mind, then that is correct: it is simply the existence of what is in the mind, and there is no difference between quiddity and existence. But if one intends thereby the quiddity that is outside the mind, this becomes equivalent to saying, “This is what exists outside the mind.” For if the external quiddity is assumed to be stripped of these necessary attributes, one could just as well assume an external existence stripped of them; and if what is in the mind is regarded as the very quiddity together with its concomitants, that is no different from saying, “This is that existence together with its concomitants.”
In either case, then, there is no distinction between existence and quiddity except the difference between what is in the mind and what is outside it. To posit a quiddity in external reality devoid of this necessary attribute is just like positing an existence in external reality devoid of it—both suppositions are false.