The Cartesian Circle

Arnauld's objection may be put as follows. Descartes appears to make the following argument.

(1) If God exists and is not a deceiver, then if I clearly and distinctly perceive that p, p is true.

(2) I clearly and distinctly perceive that God exists and is not a deceiver.

(3) If I clearly and distinctly perceive that p, p is true.

(4) So, God exists and is not a deceiver.

---> If I clearly and distinctly perceive that p, p is true.

Now, this argument, if Descartes makes it, is indeed circular. I have used the conclusion (premise (3)) in order to argue for the conclusion. Descartes can only know that God exists and is not a deceiver if he knows that his clear and distinct perceptions are true. But he can only know that his clear and distinct perceptions are true if he knows that God exists and is not a deceiver.

Various solutions to this problem have been offered by commentators down through the years. Here I am only interested in the very best solution that has been proposed (or at least, one version of it). The solution is to argue that it is not the case that there are two things to know, namely,

(a) If I clearly and distinctly perceive that p, p is true

and

(b) God exists and is not a deceiver.

These two things are really just the same thing. There is just one thing to know. That is, 'If I clearly and distinctly perceive that p, p is true' is the same thing as 'God exists and is not a deceiver'. That is, (a) = (b).

This argument may be put as follows:

(1) To say that it is possible that it is false that ''If I clearly and distinctly perceive that p, p is true", is to say that it is possible that it is false that God exists or that God is not a deceiver, since these two possibilities are the only two possibilities for the falsehood of ''If I clearly and distinctly perceive that p, p is true".

(2) So, "It is possible that it is false that ''If I clearly and distinctly perceive that p, p is true"" = "It is possible that it is false that God exists or that God is not a deceiver".

(3) So, ~"It is possible that it is false that ''If I clearly and distinctly perceive that p, p is true"" = ~"It is possible that it is false that God exists or that God is not a deceiver".

(4) So, necessarily "God exists and is not a deceiver"= necessarily "If I clearly and distinctly perceive that p, p is true".

(5) Necessarily, God exists and is not a deceiver/Necessarily, if I clearly and distinctly perceive that p, p is true.

--> There is no circularity in the single claim that "Necessarily, God exists and is not a deceiver/Necessarily, if I clearly and distinctly perceive that p, p is true."

This argument may be put in the following way (for simplicity, omitting 'necessarily' throughout). When I clearly and distinctly perceive that God exists and is not a deceiver, I clearly and distinctly perceive that it is false that God does not exist, or that God is a deceiver. These are not two different clear and distinct perceptions, but the same clear and distinct perception.

But when I clearly and distinctly perceive that it is false that God does not exist, or that God is a deceiver, I clearly and distinctly perceive that it is false that it is possible that my clear and distinct perceptions are not true. These are not two different clear and distinct perceptions, but the same clear and distinct perception.

But when I clearly and distinctly perceive that it is false that it is possible that my clear and distinct perceptions are not true, I clearly and distinctly perceive that my clear and distinct perceptions are true. These are not two different clear and distinct perceptions, but the same clear and distinct perception.

So, when I clearly and distinctly perceive that God exists and is not a deceiver, I clearly and distinctly perceive that my clear and distinct perceptions are true. These are not two different clear and distinct perceptions, but the same clear and distinct perception.

The soundness of this argument hinges on the truth of premise (1), namely, that there are only two possibilities as to why clear and distinct ideas are not true: that God does not exist, or that God is a deceiver. This is something that Descartes does believe. But is it true? Arguably, yes.

If it is true, then Descartes is not arguing in a circle. The conclusion reached at the end of Meditation IV, that God exists and is not a deceiver, just is the conclusion that my clear and distinct perceptions are true. It just is the end of the doubt about my clear and distinct perceptions. (I say Meditation IV because, although Meditation III establishes that God exists and is not a deceiver, Meditation IV must validate that by showing that my making mistakes over perceptions that are not clear and distinct does not affect the truth of the conclusion that God is not a deceiver). The conclusion that God exists and is not a deceiver just is the conclusion that I can rely upon my clear and distinct perceptions. They are the same conclusion. It is true that he can only know that God exists and is not a deceiver if he knows that his clear and distinct perceptions are true. But that's okay, because he does know that -- because it's the same thing. There is no circle.

Compare the following: he can only know that 2 x 2 = 4 if he knows that the square root of 4 is 2. But that's okay, because he does know that -- because it is the same thing.

Does this entail that there is no problem with Descartes's argument? No. There is a problem with his argument. The problem with his argument that he assumes the truth of  "Necessarily, God exists and is not a deceiver/Necessarily, if I clearly and distinctly perceive that p, p is true."

However, the problem of assuming something to be true is not the problem of arguing in a circle.