xxxiv.), must at the same time have an adequate idea or true knowledge of his knowledge; that is, obviously, he must be assured.

Q.E.D.
Note .-- I explained in the note to II.xxi.what is meant by the idea of an idea; but we may remark that the foregoing proposition is in itself sufficiently plain.

No one, who has a true idea, is ignorant that a true idea involves the highest certainty.

For to have a true idea is only another expression for knowing a thing perfectly, or as well as possible.

No one, indeed, can doubt of this, unless he thinks that an idea is something lifeless, like a picture on a panel, and not a mode of thinking--namely, the very act of understanding.