[This is a graduate seminar paper, published in Summa Philosophiae (1997). --mh]

The Cartesian Circle Persists

I have one further worry, namely how the author avoids reasoning in a circle when he says that we are sure that what we clearly and distinctly perceive is true only because God exists.
      But we can be sure God exists only because we clearly and distinctly perceive this. Hence, before we can be sure that God exists, we ought to be able to be sure that whatever we perceive clearly and evidently is true.(1)

Descartes scholars have exercised themselves over getting Descartes out of this apparently devastating objection of Arnauld's. I believe that the circularity objection cannot be avoided, and Descartes simply did commit the error Arnauld criticizes. I will presently consider some proposed interpretations of Descartes designed to save him, and explain why none of them escapes the circularity problem.

1. The obvious interpretation

The first impression one is left with upon reading the Meditations, and I think the most natural, is precisely the one Arnauld has: namely, that Descartes attempted to prove God's existence by appeal to clear and distinct perceptions; whereas he tried to validate clear and distinct perceptions by appeal to God's veracity.

As this yields a transparent circularity problem, no further discussion is required; except perhaps to note that this does not constitute a decisive objection to this interpretation qua interpretation of Descartes. It is by no means to be assumed that great philosophers are any more immune to logical errors than the rest of us.

2. The memory interpretation

The second interpretation is that Descartes' argument is not circular, because, while he proves God's existence by appeal to clear and distinct perception (hereafter, "intuition"), he is not trying to prove the reliability of intuition by appeal to God's existence. Rather, the reliability of intuition has been assumed all along. The doubt he tries to set to rest by appeal to God's existence is a doubt as to the reliability of memory, as used in the case where we remember a clear and distinct perception. Thus, Descartes' answer to Arnauld:

I have already given an adequate explanation of this point in my reply to the Second Objections ... where I made a distinction between what we in fact perceive clearly and what we remember having perceived clearly on a previous occasion. To begin with, we are sure that God exists because we attend to the arguments which prove this; but subsequently it is enough for us to remember that we perceived something clearly in order for us to be certain that it is true. This would not be sufficient if we did not know that God exists and is not a deceiver. (171)

This suggests that the problem is that, when we remember having intuited something, we might not have in fact intuited it; but knowledge of God insures the reliability of our memory.

This interpretation has generally been rejected on grounds of textual indefensibility. Where the allegedly circular argument originally appears, Descartes clearly says that God's veracity validates our clear and distinct perception; he says nothing about our memory:

Now, however, I have perceived that God exists ... and that he is no deceiver; and I have drawn the conclusion that everything which I clearly and evidently perceive is of necessity true. (48)

Descartes goes further to claim that all other knowledge depends on the knowledge of God:

Thus I see plainly that the certainty and truth of all knowledge depends uniquely on my awareness of the true God, to such an extent that I was incapable of perfect knowledge about anything else until I became aware of him. (49; emphasis mine)

This will be important to keep in mind when considering the subsequent interpretations of Descartes as well.

However, my present purpose is not primarily to show that this interpretation of Descartes is inaccurate. Rather, my argument is this: even if this interpretation were accurate, Descartes would still be open to the charge of circularity. Immediately following the above quotation discussing the proof of the reliability of intuition (from p. 48), Descartes continues,

Accordingly, even if I am no longer attending to the arguments which led me to judge that this is true, as long as I remember that I clearly and distinctly perceived it, there are no counter-arguments which can be adduced to make me doubt it, but on the contrary I have true and certain knowledge of it. (48)

Now if the arguments in question were arguments to the reliability of memory, then to say, "Well, I remember having made these arguments -- i.e. having once demonstrated the reliability of my memory" would be obvious question begging. Thus, on this interpretation, only if you kept the proof of the reliability of memory in mind all the time, so as to be constantly intuiting it, would it render your other, recollected intuitions certain. But clearly Descartes does not think you need to do this.

3. The defeasibility theory

According to the third interpretation, Descartes never tried to give a positive proof of the reliability of intuition. Rather, he tried only to defend the consistency of our intuition. That is, he only tried to show that you cannot, by using reason, adduce grounds for doubting the reliability of reason. This conforms to one plausible definition of certainty: i.e., a belief is certain if there are no grounds for doubting it; but 'grounds for doubt' must be taken from the belief system of the believer. Alleged grounds that the subject does not believe in to begin with, don't give him a reason to doubt what he does believe:

Now if this conviction is so firm that it is impossible for us ever to have any reason for doubting what we are convinced of, then there are no further questions for us to ask: we have everything that we could reasonably want. What is it to us that someone may make out that the perception whose truth we are so firmly convinced of may appear false to God or an angel, so that it is, absolutely speaking, false? Why should this alleged 'absolute falsity' bother us, since we neither believe in it nor have even the smallest suspicion of it? (103)

What this passage makes clear is (1) that certainty is attained if you believe something and there is no reason to doubt it; and (2) that only things that you presently believe (or at least suspect) can count as reasons for doubt; i.e., if you don't believe p, then p can't be a reason for you to doubt anything. Thus, to show that his intuitions are certain, Descartes needs only to show that, from within his belief system, no grounds for doubting intuition can be given.

Prima facie, it might seem that this is a task Descartes has a chance of performing. Once he has proved God's existence and veracity, the belief in these things remains in his belief system even while he is not attending to the proofs. And neither these beliefs nor any other (present or remembered) clear and distinct perceptions can be called into doubt, as long as the belief in God's veracity remains. Descartes makes clear that only a doubt about God's existence or veracity could provide reasons for doubting his clear and distinct perceptions (103); but since a ground for doubt must be something you believe (principle #2 above), no reasons for doubting his clear and distinct perceptions can arise once Descartes thinks that God exists and is not a deceiver.

Of course, if the project were to start from the skeptic's position -- namely, doubting everything, including the reliability of all of your cognitive faculties -- and thence proceed to prove various things, the project would certainly be hopeless. But if Descartes gets to start from his present belief system, including trust in his reason, and merely fend off attacks by skeptics, then he might possibly succeed. Thus, Descartes seems to neatly escape Arnauld's objection, and to do so by means of things he more or less explicitly says in reply to the circularity charge (all on p. 130).

But look closer. Consider Descartes' state of mind before he gives the proof of God's existence and veracity, and consider whether he could move from that state to the state of believing in God's existence and veracity, without using any circular reasoning. Presumably there was some time when Descartes did not yet believe that God exists and is not a deceiver (I will disregard the possibility that he was born knowing it). At the point at which Descartes does not yet know that God is no deceiver, the deceiving God hypothesis has cast doubt on everything -- this much Descartes admits. So, just as Arnauld points out, it has cast doubt on whatever premises Descartes might want to use to prove God's veracity. So such premises cannot be relied on in the proof.

We might just as well consider the case of the atheist:

The fact that an atheist can be 'clearly aware that the three angles of a triangle are equal to two right angles' is something I do not dispute. But I maintain that this awareness of his is not true knowledge, since no act of awareness that can be rendered doubtful seems fit to be called knowledge. Now since we are supposing that this individual is an atheist, he cannot be certain that he is not being deceived on matters which seem to him to be very evident (as I fully explained)... So he will never be free of this doubt until he acknowledges that God exists. (101)

But how should the atheist come to acknowledge that God exists? Not by reading Descartes' arguments. For, when Descartes premises, "Something cannot come from nothing" at the start of the argument, the atheist cannot yet know that to be true -- as he has not yet acknowledged God's existence, and Descartes has just told us that nothing else can be known until one acknowledges God's existence.

We have supposed that, in answering the skeptic, Descartes gets to rely on his present beliefs. Now, if he already believed that a veracious God existed, then the skeptic could raise no grounds for doubt, and Descartes would successfully defend the certainty of his beliefs. But that isn't the case. Descartes doesn't start out believing that a veracious God exists. He starts out in an agnostic position, and tries to prove God's existence and veracity. But in the agnostic position, he cannot be certain that, for example, 'something cannot come from nothing'; so his proof cannot get off the ground.

Although he does say in the First Meditation that he has long believed in God, Descartes does not there say that he has long believed that God couldn't deceive him; furthermore, he says about the atheists, "Let us not argue with them, but grant them that everything said about God is a fiction" (14) -- so that it appears Descartes' arguments in the Meditations are intended to be of possible use to an atheist. Furthermore, at the start of the Third Meditation, he says he is not yet sure whether there is a God (25). Indeed, only the supposition that God's existence is not being taken as part of his starting position makes sense of why any argument is needed for the existence of God in the Third Meditation.

Frankfurt claims that Descartes' argument shows that the exercise of reason leads to the conclusion that reason is reliable.(2) This just is not so. Frankfurt's interpretation of Descartes, even if correct exegetically, simply does nothing to acquit Descartes of the charge of circularity. The exercise of reason, prior to your believing in a veracious God, leads to mistrust of all conclusions; the exercise of reason after that does not lead you anywhere, since you have no premises to rely on; in particular, it does not lead you to belief in a veracious God.

Perhaps it can be maintained on Descartes' behalf, that the game Descartes is playing with the skeptic works like this: Descartes gets to start with all his beliefs intact. Then the skeptic gets to try to adduce grounds for doubting them, by working from within that belief system. If he can't, then Descartes gets to keep his beliefs. But even if he can, Descartes gets to try to answer those grounds for doubt, again working from within his present belief system. If he succeeds, he again gets to keep his beliefs; whereas if he fails, he has to relinquish them.

Thus, perhaps Descartes has won in this game: He started believing all his clear and distinct perceptions (as, e.g., that the interior angles of a triangle add up to two right angles). The skeptic adduced these grounds for doubt: God could deceive you about this. But, before accepting this and doubting all his intuitions, Descartes gets to answer the skeptic's supposition, by appealing to things he believes in. He believes that something can't come from nothing, that he has an idea of a supremely perfect being, &c.; and these beliefs provide refutation of the skeptic's supposition. In other words, Descartes can escape the charge of circularity, because the skeptic's doubt doesn't get off the ground to begin with. It's not a legitimate doubt, because it can be refuted from within Descartes' belief system.

Yet this move does not work either. Descartes cannot answer a skeptical argument by relying on something that the argument calls in question. To make the issue clearer, consider the dream argument as an analogy: I say, perhaps, "I am sitting in front of my computer right now." The skeptic says, "How do you know you're not dreaming?" If I can answer this challenge, I get to continue to believe I'm sitting in front of the computer; but if not, then not. So suppose I say, "Okay, I grant this: if I can't tell whether I'm dreaming, then I don't know whether I'm in front of the computer. So I will forthwith verify that I'm not dreaming." Then I call up a friend on the telephone and say, "Bryan, am I dreaming right now?" and Bryan assures me that I am not. "Thank you," I say, "I just had to resolve a skeptical doubt."

Surely this procedure is not legitimate. The problem is that I have relied on one of the beliefs or cognitive procedures that the skeptic's doubt is directed against, in order to answer it. The skeptic will just ask how I know I didn't just dream that my friend told me I'm not dreaming. Will I answer this by calling the friend again and asking him whether I dreamt the first call? This doesn't seem to help.

Similarly, Descartes needs to explain how he knows that God or the evil genius, or whatever else caused his existence, hasn't just deceived him into thinking that something can't come from nothing.

The present attempt to defend Descartes relies on a sort of prior claim or presumption of his present beliefs, and so we might think that Descartes can use his present beliefs in the premises of the proof of God's existence, rather than immediately having to doubt them when the skeptic raises the possibility that there is no God.

Well, suppose I am an atheist, and I would like to acquire some knowledge. Descartes seems to hold out that possibility for me. Now here are two sets of beliefs I have: (1) the beliefs comprising the premises of Descartes' proofs of God's existence; (2) the belief that God does not exist. Since I can be presumed to have both of these sets of beliefs right now, it's unclear why either of them would have a prior claim. Beliefs (1) cast doubt on -- indeed, they completely refute -- belief (2). However, it's equally true that (2) casts doubt on (1). And neither (1) nor (2) has a prior claim. If all my present beliefs get to start out with a presumption of truth, then (2) deserves that presumption just as much as (1). And so it really doesn't make sense that Descartes could use (1) to refute (2), while the skeptic is debarred from using (2) to call (1) into question.

4. The psychological interpretation

Our last Descartes interpretation holds that Descartes was not so much interested in providing good reasons for believing in God and trusting our intuitions, as with showing how you could reach a state in which you were psychologically incapable of doubting your intuitions.

According to this view, in the first place, Descartes holds that you cannot doubt an intuition while you are having it. Thus, when you go through the demonstration of God's existence and veracity, you are unable to doubt that a non-deceiving God exists. Also, when you go through any demonstration whatever, you are unable to doubt its conclusion.

Second, when you are no longer attending to, say, the proof of the Pythagorean Theorem, but you remember that you once proved it, then it is possible to doubt it.

However, if you have once proved God's existence, and you retain some memory of the proof (such that you are capable of reproducing it), you possess the means of fending off any doubts about the Pythagorean Theorem, because repeating the proof of God's existence would make you incapable of doubting that what you once intuited is true. So having the proof of God's veracity in memory renders you capable of fending off doubts about all intuitions. And it's in that sense that Descartes shows you can reach a state of certainty.(3)

Of course, if this were the aim, you wouldn't need to remember the proof of God's existence; all you would need is to remember the proof of the Pythagorean Theorem. That is, in order to attain certainty in this psychological sense of being able to fend off doubts about a belief that p, all you would need is to retain the ability to reproduce the proof of p. Then, if skeptical doubts start to arise, you are able to reproduce the proof and thus become again psychologically incapable of doubting that p. In other words, any clear and distinct perception could be certain knowledge, even when it was only recollected, even for an atheist -- which Descartes expressly denies (49, 101).

I believe this approach needs to be combined with the previous one. What should happen to an atheist is this: First, he doesn't believe in God, so he must doubt everything that he has clearly and distinctly perceived, while he is merely remembering it. Then, he attends to the proof that God exists and is not a deceiver. He is forced to believe it while he attends to the demonstration; so he is psychologically compelled to add the belief in a veracious God to his belief system. And, once he has added it, it is no longer possible for skeptics to raise doubts about any of his clear and distinct perceptions, as was explained in section 3. Thus, the only problem is getting the belief in God into his head to begin with -- once that is done, even if he forgets how the proof goes, he can no longer have reason to doubt his intuitions. The ability to reproduce the proof is irrelevant, on this view, and so is the question of whether the atheist had good reason to accept the existence of God.(4) What counts is this: he can be compelled to accept the existence of God; and then, after that, he cannot be given reasons to doubt the reliability of intuition from within his belief system.

Does this approach at last escape circularity?

We have conceded that Descartes intends to raise no doubt about the reliability of memory. Thus, if you remember that you clearly and evidently demonstrated that p, you may take it as given that you did clearly and evidently demonstrate it. And -- again, since the reliability of memory is not in question -- in general, if you remember that p, you may take it as given that p.

Keeping this in mind, why is it, again, that the atheist cannot have genuine knowledge? Let p = the proposition that the interior angles of any triangle add up to two right angles. Suppose that I, an atheist, demonstrated that p yesterday. And now I assert p. Why don't I know it? Descartes holds that I couldn't doubt that p yesterday, when I did the proof; but I can doubt it today, because I'm no longer looking at the proof, but merely remembering it. But, unless the reliability of memory is being questioned, why doesn't my memory that p, constitute certain knowledge that p? That is, why don't I just say to the skeptic that I remember that the interior angles of a triangle add up to two right angles -- not, mind you, that I remember that yesterday I believed this in a peculiarly compelling way, but that I remember that it is true?

Perhaps Descartes would answer that I can only remember my own past experiences, so I cannot directly remember the truth of p, but only my psychological attitudes towards p. Descartes would have to say this, if he's going to allow me to doubt that p is true, without doubting that I clearly and distinctly perceived p. So let us take it that this is Descartes' view: My present (alleged) knowledge that p is not simply a memory of the truth of p; rather, it is an inference from the premises

(A1) that I clearly and distinctly perceived p yesterday (which I know by memory); and
(A2) that everything I clearly and distinctly perceive is true.

Yesterday's knowledge that p wasn't like this; it was just based on some mathematical premises. None of the premises of yesterday's knowledge was psychological in content, nor acquired through memory. So I can doubt that p today, because I can doubt the major premise from which it is inferred (A2). I couldn't doubt that p yesterday, in spite of doubting (A2), because (A2) wasn't a premise in yesterday's inference.

We have now understood why the atheist can doubt his clear and distinct perceptions while he's only recollecting them; so we understand why one cannot have genuine knowledge unless one knows that God exists. But now, why is it that the believer can have genuine knowledge? Why, again, can he not doubt his clear and distinct perceptions when he is merely recollecting them? Well, he knows that God exists, and that guarantees the truth of the major premise "Whatever I clearly and distinctly perceive is true". But how does he know that God exists? If he is presently attending to the proof of God's existence, then there is no problem; that makes him unable to doubt it. But Descartes clearly wants to say the believer has certainty even when he is no longer attending to the proofs of God's existence (48). So, assuming that the theist is not presently attending to these proofs, how does he know that God exists? The obvious answer thrusts itself forward: because he remembers it. Now, does he directly remember that God exists, or does he merely remember that he once clearly and distinctly perceived that God exists (where "perceive" is taken in a purely psychological sense, i.e., not as a success verb)? To be consistent with what we just said about the atheist, we must say that the theist remembers merely that he once intuited that God exists. So whereas the atheist's total direct knowledge at present is

(A1) Yesterday I intuited that p.

the believer's total direct knowledge is

(B1) Yesterday I intuited that p.
(B2) I also intuited that whatever I intuit is true.

from which the conclusion that p no more follows than in the first case. The believer is still lacking the major premise "Whatever I intuit is true." If he cannot directly remember that fact, but must infer it from the fact that he once intuited that whatever he intuits is true, then he is evidently caught in a circle. Furthermore, given that the believer, if he is intelligent, will also remember that the argument by which he concluded "Whatever I intuit is true" was, while psychologically compelling, logically flawed, it is still more doubtful that he will infer that whatever he intuits is true on the basis of his memory of having demonstrated it.

And if the believer does know that whatever he intuits is true -- without having to infer it from the fact that he once intuited it -- then why may not the atheist know that the interior angles of a triangle add up to 180 without having to infer it from the fact that he once intuited it?

One is tempted here to say that the believer's position is different because he lacks something that the atheist has. The theist believes that whatever we intuit is true, while he lacks any belief that would undermine the premise that whatever we intuit is true. The atheist also believes that whatever we intuit is true, but he has another belief that undermines the premise that whatever we intuit is true. Thus, the atheist has grounds for doubt that the theist lacks. But the question is, how may the theist believe that whatever he intuits is true? Not because he intuits it, for he cannot be expected to keep his attention focused on this intuition all the time.

Because he remembers that he intuited it? But that premise does not support the desired conclusion; from the fact that he intuited that whatever he intuits is true, it follows that whatever he intuits is true only if one assumes that all intuitions are true.

Because he remembers simply that whatever he intuits is true, then? But why may not the atheist likewise remember simply that the interior angles of a triangle add up to 180? Well, perhaps he does, but then he also remembers that there is no God, and that can cause him to doubt the first conclusion. But why should it do that, since we have said that the reliability of memory is not being questioned, and since on the present hypothesis, "Whatever I intuit is true" is not a premise in the atheist's reasoning?

The upshot of this discussion, then, is that Descartes cannot make any principled distinction between the atheist's (alleged) knowledge that p, and the theist's (alleged) knowledge that whatever he clearly and distinctly perceives is true. This means that Descartes must either accept that the atheist has genuine knowledge -- and hence, that clear and distinct perception does not require validation by theology -- or accept that the theist does not have knowledge.


1. From the fourth set of Objections to the Meditations, CSM II, 150. Future page references are to CSM II.

2. "Descartes' Validation of Reason", American Philosophical Quarterly, April 1965 (149-56).

3. Louis Loeb, "The Cartesian Circle", in The Cambridge Companion to Descartes (200-35).

4. This is my own synthesis of Frankfurt and Loeb. It is not something that either of them would agree to.