Clear and Distinct Ideas. The Cartesian Circle.

Descartes is a rationalist. The cogito argument rests on an acceptance of an idea that is immediately present to his mind - not on experience or deduction (although this could be disputed). The thought that if he is thinking then he must exist is the first "clear and distinct idea". He intuits it directly, by pure thought. By "clear" Descartes means that the idea is open and present to the attending mind. By "distinct" he means that it is a precise, separated, sharply defined idea, not mixed up with other ideas or concepts.

The point is that at the time we rationally "perceive" the idea, its truth cannot be doubted. It is self-evident.

But what about when we are not attending to the idea, when we are not "perceiving" it directly? Does it cease to be true? What could make it true when we aren't thinking about it? Does its truth come and go?

One obvious response would be to say that memory makes it true. We remember that it is an idea we have previously perceived to be self-evidently true. But memories themselves can be confused, vague and inaccurate; and they are not demon-proof. So far there is only one demon-proof idea, for even if the demon is tricking Descartes about every other idea (and every memory), he cannot be tricking him about his existence.

So Descartes needs something other than memory that can establish enduring truths, truths that remain certain even when not be directly attended to. But having established that clear and distinct ideas are self-evidently true in the case of the cogito, he can now use them to establish the existence of God. Once he has established the existence of an omnibenevolent God he can be sure that God would not permit him to be systematically deceived. Some of his sense perceptions may be illusions, but his clear and distinct ideas, which are purely intellectual and not linked to the body, can surely be trusted. This means he can trust them to be true enduringly, even when not attended to.

The Cartesian Circle

This is a famous objection to Descartes' use of clear and distinct ideas. It is claimed that he argues in a circle, as follows:

1) I am certain that God exists because I am certain of whatever I clearly and distinctly perceive.
2) I am certain of what I clearly and distinctly perceive because I am certain God exists.

This would obviously be an unacceptable form of argument. But Descartes denied that he was arguing circularly. He said we can trust clear and distinct ideas without relying on God, but only at the time of the "perception". Once we have proved the existence of God (who by definition must endure when we are not perceiving his existence by pure thought), we can claim that we have enduring knowledge of him and his goodness, and that therefore we can trust our clear and distinct ideas not to be only temporarily true. Once we have proved even fleetingly the existence of God, we can be sure that we are not being systematically deceived by the demon - and therefore that what we clearly and distinctly perceive to be true is true enduringly, even when we are not attending directly to the idea.

Not everyone is satisfied by this response. You must decide whether you think Descartes'clear and distinct ideas theory, on which his whole philosophy depends, really does avoid the Cartesian Circle objection.