woensdag 28 november 2012

Descartes' ideas

Descartes knows that he is a thinking thing. This knowledge implies a criterion for certain, indubitable knowledge. If one doubts that means that one thinks. I am doubting now, therefore I am thinking now. I see this both clearly and distinctly, that is to say this knowledge is present to my mind and I distinguish the idea of myself thinking accurately from other ideas. I could not be certain of the fact that I am thinking if clear and distinct ideas  could ever be false. So I can now say that everything that I perceive clearly and distinctly is ipso facto true.
         If spelled out, Descartes argument goes like this:

(1)It is certain that I am thinking if I am doubting
(2)That I am thinking if I am doubting is clear and distinct knowledge
(3)If something is clear and distinct, then it cannot be false
(4)That I am thinking if I am doubting is clear and distinct (from 2)

(5)That I am thinking if I am doubting cannot be false (from 3 and 4)


The point, then, is to find out what other beliefs, if any, can be shown to be necessarily true. It is in this context that Descartes will present his two arguments for the existence of God. In the third Meditation the question is of what I can be sure, and more particularly of what beliefs about the external world (reality independent of me) I can be sure that they are true.
         It seems a hard and fast fact that two and three make five. But even what seems most certain could be false if there were a God who deceived me. Even if I am being deceived, however, I am still thinking, of that I am sure. And I have no reason to think there is a deceiving God; moreover, I don’t even know if there is a God in the first place. Since God has this architectural spot in the argument, it is crucial to find out if He exists. The concept of God is central to the argument.
         Strictly speaking, Descartes’ arguments concern thoughts or beliefs.
He divides thoughts into several different classes.
How do I know if the thought that God exists is necessarily true? To answer this question Descartes investigates the concept of the idea. An idea is an image of a thing. I have an idea of something if I think of that something, a man, a heaven, a chimera, an angel, or a God. Thoughts can also have other forms, volition, fear, assent, denial that also take something as the object of the thought. The idea here is not just the image that is similar to the thing it pictures. These classes or ways of thought can be divided into volitions, passions and judgements.
         If an idea is considered simpliciter it cannot be false in the strict sense. “Whether I imagine a goat or a chimera, it is equally true of both I that I imagine them”. Volitions and wishes also cannot be false: I can wish something to be the case and thereby it is not false that I so wish. The only class of thought that is strictly speaking either true or false is a judgement. I can only make a mistake when I take an idea to refer to something outside of me. As long as I merely consider ideas as modes of thought they can hardly lead me astray.
         The next question Descartes asks is where the several ideas have their origin. Some ideas are innate, such as the ideas of things, truth and thought, others I have acquired such as sound, sun and fire (they come from outside of me), yet again others, such as sirens and hippogryphs, I have produced myself. In Meditation 3 Descartes is interested primarily in ideas that come from outside of me – ideas of the external world.
         Why do I consider particular sorts of ideas to be equal to the things of which they appear to be images?

God's existence in Descartes' fifth Meditation


How do I know that God exists? More particularly, how do I know that he is not a figment of my imagination? I find within myself the idea of the most perfect being, of which I understand that existence is part of his nature. Although I can distinguish between existence and essence, I cannot separate existence from God anymore than I can separate triangularity from a triangle, or a mountain from a valley. I cannot think of God without existence just as I cannot conceive of a mountain without a valley.
         There is an important logical difference between the conception of a mountain with a valley and the conception of God together with existence. The fact that a mountain cannot be thought without a valley, does not imply that mountains must exist; it only implies that if a mountain exists, there must be a valley as well.
In the terms of mathematical logic, we could perhaps analyze it, not as an existentially quantified sentence, but as a universally quantified one, Necessarily, for all x and all y, if x is a mountain, and y is a Valley, then there is a relation between x and y. But it need not be the case that a mountain exists. There is nothing contradictory about a flat earth. That is why one uses a universal instead of an existential quantifier. Shouldn’t we say the same thing about God? If I think that God, if He exists, also exists, that doesn’t imply that He exists.
         That argument clearly isn’t cogent. As it stands it is a tautology and therefore proves nothing. All it says, one is tempted to say, is that there is an x and x is God. It shows that we cannot conceive of an existing God without conceiving of His existence. Could we conceive of God at all without existence? Descartes holds that we cannot.
         Of course, using mathematical logic here is ahistorical. Though Russell read Descartes, Descartes did not read Russell. On a common reading ‘exists’ in Descartes argument functions as a predicate. It is precisely this use that Kant indicted in his purported refutation of what he, perhaps infelicitously, called the Ontological Argument. Existence according to Kant is not a predicate. As we have seen in the paragraph on the objections to St Anselm’s proof however, sometimes one does need to use ‘exist’ as a predicate, or in any case, to say that such and such a thing does exist. However that may be, using an existential quantifier to express the thought that the concept of God involves the concept of existence goes awry. If we merely say that there is an x such that x is God; the existence of God does not follow from an explicitation of the concept, rather God is said to exist. A judgement about God’s existence is put forward here. It therefore misrepresents Descartes’ argument to put it in terms of mathematical logic. It is better therefore to leave mathematical logic to the side here and to continue thinking about Descartes’ arguments for the existence of God in the terms in which he discusses them.
I cannot think of God, Descartes holds, without His existence. Therefore God cannot be separated from existence, so He must exist. God cannot be separated from existence because He is the most perfect being. Since existence is the highest perfection, it is impossible to conceive of God without existence. A non-existing God is logically impossible to conceive of, whereas one could conceive perfectly well of both, say, a horse with wings, and one without.
         The objection to this line of reasoning lies to hand. What if the posited proposition, ‘God possesses all perfections’ is not itself necessary? Descartes retorts that if I think of God I necessarily attribute all perfections to Him in the same way as thinking of a triangle implies thinking of a figure with straight sides and three angles.
         Moreover I cannot conceive of anything else whose existence is part of its essence.
         The big question looming largely is why the professed certainty Descartes ascribes to his concept of God should be any reason for taking the propositions that follow from this concept to be true. Descartes’ proof in the fifth Meditation turns on his concept of truth. It is when we know what Descartes holds truth to be that we are able to understand why it is that he purports to be able to show that God exists by purely a priori argument.
         In the third Meditation Descartes states that he considers an idea to be true if he sees it clearly and distinctly. The definitions of these crucial notions can be found in Descartes’ Principles of Philosophy, section 45. For an idea to be clear is for it to be present and accessible to the attentive mind. An idea is distinct if it is clear and sufficiently acutely separated from other perceptions to contain just that which is clear. So if an idea is true, it is present to my mind, I see it for what it is and I can tell it apart with great precision from other ideas. If we return to the third Meditation we see that ideas themselves strictly speaking aren’t true or false. Ideas are true or false only if they pertain to other things than themselves. If I have the idea of a flying horse that idea is not false; it would only be false if I judged that there was such a thing. Truth and falsehood in a strict sense are properties only of judgements. My idea of God is true or false only if I judge that He exists or doesn’t exist.
         The judgement that God exists must be true, Descartes holds, since it is clear and distinct. It cannot be the case that I clearly and distinctly perceive an idea which is not by virtue of its being so perceived, true.
         Descartes’ exposition of his idea of truth is closely involved with his first proof of God’s existence in the third Meditation. It is this proof that I turn to next. Then I shall discuss if the proofs cohere and how they reflect on the proofs of St. Anselm and St. Augustine.