The most pressing task seems to be to try to escape from the doubts into which I fell a few days ago, and see whether any certainty can be achieved regarding material objects. M5 p44
With his criterion of clarity and distinctness now guaranteed by God, and an understanding of how and why he has been mistaken in the past, Descartes continues to rebuild his knowledge. He turns his attention to material things, examining their ideas to discover their true nature. This examination leads him to a second argument for the existence of God, the Ontological Argument.
Over the course of his investigation, Descartes has delayed any enquiry into whether material things actually exist independently of him, and instead has reflected solely on the ideas that he possesses. This method is characteristic of his rationalist approach and is informed (once again) by mathematics. It may seem odd not to begin with existence, but arithmetic and geometry are concerned with objects whose real existence is uncertain – numbers, perfect circles and so on. These disciplines investigate the nature or essence of such concepts independently of any real existence they may have. Descartes follows this model, embarking on a purely phenomenological investigation of his ideas in an attempt to identify their essential nature.
He is, in effect, laying the groundwork for the new Cartesian physics. Matter is essentially nothing more than what can be described geometrically – ‘the subject-matter of pure mathematics’ (p49). As he suggested in the passage regarding the piece of wax in the Second Meditation, the true nature of material things can be reduced to extension, size, shape, position, number, motion and duration. These primary qualities, and these alone, are all distinct and ‘transparent to me’ (p44). More than that, they can be known a priori and are beyond doubt.
I always held that the most certain truths of all were the kind which I recognized clearly in connection with shapes, or numbers or other items relating to arithmetic or geometry, or in general to pure and abstract mathematics. M5 p45
Fundamental ideas like extension and quantity are, for Descartes, innate ideas. There is an oddly Platonic flavour to his account in this Meditation. He describes his immediate grasp of such a priori truths as like ‘noticing for the first time things which were long present within me’; and, even more explicitly, ‘remembering what I knew before’ (p44). And, like Plato, Descartes believes that rational analysis of concepts yields new truths which he can clearly and distinctly recognise as true. In the case of geometry, this includes various geometric properties of triangles. Applying the same analysis to the concept of God leads to the Ontological Argument:
... [if] everything which I clearly and distinctly perceive to belong to that thing really does belong to it, is not this a possible basis for another argument to prove the existence of God? M5 p45
Together with the Trademark Argument of Meditation Three, this constitutes Descartes’ proof of a God who can guarantee the truth of his clear and distinct perceptions.
Descartes’ method for establishing the grounds for certain and reliable knowledge is open to a serious objection, one which was identified at the time by critics like Antoine Arnauld. Cottingham puts it like this:
It might be objected at the outset that the task Descartes has set himself here is an impossible one: if there can be no reliable knowledge until after God’s existence is proved, then how will it be possible to construct a reliable proof of God’s existence in the first place? Cottingham p48
This problem is generally known as the ‘Cartesian Circle’, as it suggests that Descartes’ claim to provide a divine warranty for his beliefs involves circular reasoning. The two elements of his method – clear and distinct perception, and the goodness of God – seem to depend upon each other to be valid: we can trust those perceptions because God guarantees their truth; and we can trust that God exists because we perceive the proofs clearly and distinctly. But one of them must come first, and must be established independently of the other, if Descartes is to avoid a chicken-and-egg case of circular reasoning.
The problem can be developed by noticing an inconsistency in the way Descartes tends to talk about his project. Sometimes he seems to insist that clear and distinct perception is sufficient to guarantee the truth of a belief. And sometimes he seems to claim that all knowledge, including such clear and distinction perceptions, needs God to verify it.
In support of the first claim we may remember the use Descartes made of the Cogito to generate a criterion of truth:
In this first item of knowledge there is simply a clear and distinct perception of what I am asserting; this would not be enough to make me certain of the truth of the matter if it could ever turn out that something which I perceived with such clarity and distinctness was false. So I now seem to be able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true. M3 p24 (emphasis added)
In the Second Replies, Descartes directly addresses the charge of circularity and seems to defend this claim that some intuitions need no further guarantee:
Now some [perceptions] are so transparently clear and at the same time so simple that we cannot ever think of them without believing them to be true. The fact that I exist so long as I am thinking, or that what is done cannot be undone, are examples of truths in respect of which we manifestly possess this kind of certainty. For we cannot doubt them unless we think of them; but we cannot think of them without at the same time believing they are true, as was supposed. Hence we cannot doubt them without at the same time believing they are true; that is, we can never doubt them. OR2 p105
If some knowledge can be trusted even without the guarantee of a non-deceiving God, then the problem of circularity can be solved: such intuitions can provide the premises for the proof of the existence of God, and that proven existence can then be used to guarantee other forms of knowledge.
But elsewhere Descartes seems quite clear on the fact that the existence of God is needed to guarantee any and all knowledge (including, therefore, such clear and distinct perceptions):
I must examine whether there is a God, and, if there is, whether he can be a deceiver. For if I do not know this, it seems that I can never be quite certain about anything else. M3 p25 (emphasis added)
This need for God to guarantee the truth even of clear intuitions lies behind Descartes’ curious but logical claim that an atheist can never acquire knowledge. In the Second Replies, he discusses an atheist who clearly understands a geometric truth about triangles:
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... he will never be free of this doubt until he acknowledges that God exists. OR2 p103 (emphasis added)
And here in the Fifth Meditation, after the Ontological Argument, he makes the same claim explicitly and repeatedly:
I see that the certainty of all other things depends on this [ie the existence of God], so that without it nothing can ever be perfectly known... the certainty and truth of all knowledge depends uniquely on my awareness of the true God. M5 p48-9 (emphasis added)
Both of these claims cannot be true: either all knowledge requires the divine guarantee, or some knowledge does not. If the former is the case, then it seems that Descartes cannot avoid the Cartesian Circle. For this reason, and because of Descartes’ own response to the charge of circularity, commentators have tried to distinguish these claims more precisely.
Descartes’ response in the Second Replies is worth reading at length:
When I said that we can know nothing for certain until we are aware that God exists, I expressly declared that I was speaking only of knowledge of those conclusions which can be recalled when we are no longer attending to the arguments by means of which we deduced them. OR2 p103
And then later:
... there are other matters which are perceived very clearly by our intellect so long as we attend to the arguments on which our knowledge of them depends; and we are therefore incapable of doubting them during this time. But we may forget the arguments in question and after remember simply the conclusions which were deduced from them. The question will now arise as to whether we possess the same firm and immutable conviction concerning these conclusions, when we simply recollect that they were previously deduced from quite evident principles (our ability to call them ‘conclusions’ presupposes such a recollection). My reply is that the required certainty is indeed possessed by those whose knowledge of God enables them to understand that the intellectual faculty which he gave them cannot but tend towards the truth...’ OR2 p105
The key distinction here is not different types of knowledge, but the different ways in which we pay attention to a belief. A conclusions may be clear and distinct ‘so long as we attend to the arguments’: but ‘as soon as I turn my mind’s eye away from the proof’ (p48) it becomes merely another doubtful proposition. While they are present to the mind, certain intuitions (like the Cogito) are self-verifying and need no divine support, but afterwards the memory of those intuitions – since it is less clear and distinct – can only be trusted if God is proven not to deceive. The axioms for the arguments for God’s existence – both here with the Ontological Argument and in the Third Meditation with the Trademark Argument – are clearly true, for as long as they are present to the mind. And in that time they can serve to ground the proofs of the existence of God. This defence of Descartes has become known as the ‘memory answer’, since it sees the role of God primarily as the guarantor of the truth of memories: immediate intuitions need no such guarantee.
However, not every commentator has found this position plausible (see Williams 193ff), not least because so many passages in Descartes’ writings seem openly to contradict it. It is worth remembering what Descartes says about a priori intuitions in the Third Meditation. At that point he has not forgotten his sceptical argument from a Deceiving God, and he admits that however convinced he is by such propositions, there is ‘a very slight and, so to speak, metaphysical’ doubt (p25). It seems clear from this and other passages that Descartes extends his sceptical doubt even into such clear and distinct perceptions – which means that something further (ie God) is needed to remove that doubt. But since the existence of God has not yet been proven – and cannot be proven without reliance on such clear and distinct perceptions – Descartes’ project has either stalled, or will soon require circular reasoning.
Whether or not the Cartesian Circle can be dissolved remains unclear. Perhaps at the very least we must acknowledge that Descartes himself was inconsistent in his phrasing – an inconsistency which may represent a fatal flaw to his whole programme.