and the universal accident, and the distinction they draw between the absolute and the determinate. They seized upon attributes that are identical in their scope of generality and particularity, yet declared some of them universal and others specific.

The second principle concerns their discourse on essences, their essential attributes, the difference between those and the accidental properties that necessarily accompany an essence, and the distinction between essence and existence. This second principle turns on affirmation and negation, whereas the first turns on particularity and universality. Upon these two foundations they built most of their theorizing; through them they diverged from people of sound instinct and straight reason, and because of them they fell into error and bewilderment. One of them may spend his entire life examining and investigating, yet never settles in his own mind what to say about the existence of the Necessary Existent, though that is the clearest of all truths.

The root of the mistake into which these thinkers fell—clever as they are in comparison with their followers—is that in their usage the term “essence” came to refer chiefly to what is in the intellect, whereas the word “existence” was reserved for what lies outside the intellect. The word “essence” is taken from the question “What is it?”; when the inquirer asks “What is it?” he seeks an answer, and the respondent supplies what is uttered in reply. Whatever is given in answer to that question must necessarily be conceived by the mind, whether or not it exists in external reality.

From this they concluded that an essence is other than its existence, as they state in the case of the triangle, claiming that the quiddity of a triangle is distinct from the existence of a triangle. This is correct insofar as a triangle can be conceived by the intellect without being instantiated outside it. The term “existence,” however, has come to be used mainly for what has actuality in the external world, for whatever the mind conceives—if it is not realized externally—cannot be said to exist. Thus the difference between existence and essence is the difference between mental being and external being, and this distinction is sound when understood in that way; for clear reason knows that the reality of a thing present outside the mind is not identical with the concept one forms of it