Third Meditation

Clear and Distinct Perceptions

One conclusion of Meditation II (it seems, anyway), is that "I exist" is "necessarily true every time I utter it or conceive it in my mind" (p. 30). Another conclusion, apparently, is that I am, or am at least, "a thing that thinks, that is to say, a thing that doubts, affirms, denies, understands a few things, is ignorant of many things, wills, refrains from willing, and also imagines and senses." (p. 34) That is, "I am certain that I am a thinking thing."

Descartes asks himself whether he now has a principle by which he may arrive at truths. He argues that he "clearly and distinctly perceives" that he exists, and that he is a thinking thing.

"But do I not therefore also know what is required for me to be certain of anything? Surely in this first instance of knowledge, there is nothing but a certain clear and distinct perception of what I affirm. Yet this would hardly be enough to render me certain of the truth of a thing, if it could ever happen that something that I perceived so clearly and distinctly were false. And thus I now seem to be able to posit as a general rule that everything I very clearly and distinctly perceive is true." (p. 34)

The rule that is entertained here is the Rule of Clarity and Distinctness or the Truth Rule: whatever idea or judgment I clearly (i.e. "when it is present and accessible to the attentive mind") and distinctly (i.e. "is so sharply separated from all other perceptions that it contains within itself only what is clear") perceives, is true. That is:

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

To give an example, the judgment that "something is not greater than itself" is clearly and distinctly perceived, and hence, is true. Or the judgment that "2 is greater than 1" is clearly and distinctly perceived, and hence, is true.

(Note that I have given as examples judgments, rather than ideas. Descartes talks about "what I affirm", which is a judgment, and not merely an idea. Descartes may talk in terms of ideas, but even so, these ideas have to be in propositional form to be capable of being true or false.)

However, Descartes does not, apparently, go so far as to say that this Truth Rule is itself true. He says that "I now seem to be able to posit..."

One question we might ask is whether he is fully confident that the Truth Rule is true. Immediately following the Truth Rule he says the following:

"Be that as it may, I have previously admitted many things as wholly certain and evident that nevertheless I later discovered to be doubtful. [...] But what about when I considered something very simple and easy in the areas of arithmetic or geometry, for example that two plus three make five, and the like? Did I not intuit them at least clearly enough so as to affirm them as true? To be sure, I did decide later on that I must doubt these things, but that was only because it occurred to me that some God could perhaps have given me a nature such that I might be deceived even about matters that seemed most evident. But [ 1] whenever this preconceived opinion about the supreme power of God occurs to me, I cannot help admitting that, were he to wish it, it would be easy for him to cause me to err even in those matters I think I intuit as clearly as possible with the eyes of the mind. On the other hand, [2] whenever I turn my attention to those very things that I think I perceive with such great clarity, I am so completely persuaded by them that I spontaneously blurt out these words: "let anyone who can do so deceive me; so long as I think that I am something, he will never bring it about that I am nothing. Nor will he one day make it true that I never existed, for it is true now that I do exist. Nor will he even bring it about that perhaps two plus three might equal more or less than five, or similar items in which I recognize and obvious contradiction."

It does appear here that Descartes is torn between the following two thoughts:

(1) God could give me a nature such that my clear and distinct perceptions are false.

(2) I cannot, while having a clear and distinct perception, believe that it is false; I must believe that it is true.

Even though he cannot doubt any particular clear and distinct perception while he is having one, yet he can doubt that his clear and distinct perceptions (in general) are true because of the possibility of a deceiving God.

It is important to see here that included in the list of clear and distinct perceptions is the clear and distinct perception that "as long as I think that I am something [it is not true that] I am nothing". In other words, the cogito judgment from Meditation II. However, what this means is that so long as Descartes thinks about the power of God, he accepts that God could make it the case that "I exist", when it is uttered or thought, IS FALSE.

This means that even the cogito from Meditation II is not safe from the power of God, in principle. As Descartes goes on to say:

"because I have no reason for thinking that there is a God who is a deceiver (and of course I do not yet sufficiently know whether there even is a God), the basis for doubting, depending as it does merely on the above hypothesis, is very tenuous and, so to speak, metaphysical. But in order to remove even this basis for doubt, I should at the first opportunity inquire whether there is a God, and, if there is, whether or not he can be a deceiver. For if I am ignorant of this, it appears I am never capable of being completely certain about anything else." (34-35)

If it is really true that Descartes is "never capable of being completely certain about anything else" unless he knows whether or not there is a deceiving God, then he does not know that "I exist" is true every time he judges it unless he knows whether or not there is a deceiving God.

The problem, of course, is that it now seems that he must find out if there is a God that deceives without being able to be certain about anything. But if this is so, how can he be certain about the premises of the argument used to prove the existence of God, or the goodness of God? This question will haunt Descartes later.