This affirmation involves the conception or idea of a triangle, that is, without the idea of a triangle it cannot be conceived.

It is the same thing to say, that the concept A must involve the concept B, as it is to say, that A cannot be conceived without B.

Further, this affirmation cannot be made (II.Ax.

iii.) without the idea of a triangle.

Therefore, this affirmation can neither be nor be conceived, without the idea of a triangle.