Again, this idea of a triangle must involve this same affirmation, namely, that its three interior angles are equal to two right angles.

Wherefore, and vice versa, this idea of a triangle can neither be nor be conceived without this affirmation, therefore, this affirmation belongs to the essence of the idea of a triangle, and is nothing besides.

What we have said of this volition (inasmuch as we have selected it at random) may be said of any other volition, namely, that it is nothing but an idea.

Q.E.D.
Corollary .-- Will and understanding are one and the same.
Proof .-- Will and understanding are nothing beyond the individual volitions and ideas (II.xlviii.and note).

But a particular volition and a particular idea are one and the same (by the foregoing Prop.); therefore, will and understanding are one and the same.