Philosophy

5

LECTURE: Descartes on God and the external world

As we saw last time, Descartes’ reconstruction of all knowledge begins with the Cogito argument (“I think, therefore I am”). But how can he get from knowledge of his own existence to knowledge of the existence of anything else, such as the physical world? The key step, he thinks, is to establish next the existence of God. God functions, in Descartes’ system, to provide a kind of bridge by which one can get from knowledge of oneself to knowledge of physical reality. To build this “bridge,” Descartes gives three arguments for God’s existence in the Meditations.

Bridge from thought to reality

Now, we have seen that medieval writers give various arguments for God’s existence, such as the First Way of Aquinas, which is based on Aristotle’s Unmoved Mover argument. Descartes does not give arguments of exactly that sort, for a couple of reasons. First of all, like other early modern philosophers, he is trying to move away from the Aristotelianism of the medievals. He wants to avoid an analysis of change like Aristotle’s analysis in terms of actuality and potentiality, and an Unmoved Mover argument presupposes that analysis.

Second, arguments like Aristotle’s and Aquinas’s start with facts about the physical world outside the mind, and the changes taking place in it. But Descartes, at this point in the Meditations, hasn’t yet proved that there is a physical world. He’s shown that he exists, but (so far) he doesn’t yet know that he isn’t just dreaming the physical world. So, in arguing for God, he needs to start with things he can know just by virtue of knowing himself as a thinking thing.

The preservation argument

Since this isn’t a class on either the philosophy of religion or on Descartes specifically, we won’t look at all of Descartes’ arguments for God, but will just focus on one of them. The other two, very briefly, are as follows. The first is one that commentators call the “trademark argument,” and in it Descartes tries to show that he could not even have the idea of God in his mind unless God had put it there, as kind of a divine “trademark” stamped in the intellect. The reasoning of the argument is fairly complicated, but it has never been a very popular argument even among philosophers who think that God’s existence can be proved.

Then there is the “ontological argument,” which Descartes borrows from the medieval philosopher St. Anselm. In Descartes’ version, the argument starts with the idea that God is by definition a supremely perfect being, then argues that existence is a kind of perfection, and concludes that God therefore must by definition have existence. This sort of argument has gotten much more attention in the history of philosophy, though it is very controversial.

The argument we will focus on, though, is the one that commentators call Descartes’ “preservation argument.” The basic idea is this. Given the Cogito, Descartes knows that at least he exists. But what brought him into existence? And, more importantly, what keeps him in existence or preserves him in existence at any moment, including here and now? Why is he not instead annihilated or lapsing into nothingness? How is he constantly re-created from moment to moment?

Could Descartes be causing himself to exist? Could he be preserving himself in being here and now? Descartes argues that this cannot be what is going on. The reason is this. Whatever is causing him here and now, he says, is creating him out of nothing, insofar as it is causing him to exist at all rather than lapsing into nothingness.

Now, whatever can do that – create out of nothing – can create anything at all, because the ability to create out of nothing is the fullest kind of creative power that there can be. Other kinds of creating involve taking pre-existing materials and altering them. But creating out of nothing involves using no pre-existing materials at all. It’s basically a matter of creating the materials and altering them all at the same time, in one act.

So, Descartes says, if he could create himself out of nothing, then since in that case he could make anything, he could also make himself to be all-powerful, all-knowing, and so on – in short, he could make himself God, and would do so. But obviously, he is not God, since he doesn’t have those properties. Therefore, Descartes concludes, he cannot be his own cause. So, something else must be causing him. Let’s label this cause C.

Is C itself God, or is C something less than God? Suppose it is something less than God. Then, in that case, says Descartes, C cannot be its own cause either, because if it could cause itself then it could and would make itself God, and (we are supposing) it too is not God. So C must have a further cause of its own. But this generates a regress of causes, and the only thing that could end this regress is something that does cause itself to be God – which would, of course, be God himself.

So, Descartes concludes, he is at every moment being preserved or re-created out of nothing either by God, or by some other thing which is itself preserved or re-created at every moment by God. Either way, God exists.

This is a somewhat strange argument. It conceives of God as a causa sui (Latin for “self-causing” thing), which seems to be an incoherent idea. How could something cause itself? Descartes elsewhere clarifies that he is not thinking of God as his own efficient cause, i.e. as something that exists before it exists and brings itself into existence – which would certainly be incoherent. Rather, he says that God is his own formal cause, in the sense of being something whose existence is explained by his own nature rather than by something distinct from him.

Clear and distinct perception

Descartes is arguably led into this somewhat odd way of arguing for God’s existence because of his reluctance to use any distinctively Aristotelian ideas. It seems to me that he could, if he were willing to take on board a little Aristotelianism, easily adapt Aquinas’s First Way for his own purposes. He could say that, even just starting from his own existence as a thinking thing, he knows that change is really occurring (since he knows that his thoughts change from moment to moment). And then the First Way could still proceed from there more or less the way it does in Aristotle and Aquinas.

Since (in my opinion) the First Way is a good argument for God’s existence, and (in my opinion) the arguments for God that Descartes gives are seriously problematic, I think that’s the way he should have gone. But he didn’t ask me for advice.

Anyway, suppose that Descartes can get some argument for God’s existence off the ground. How does God serve as a “bridge” to knowledge of other things?

Descartes answers this question in the Fourth Meditation (which is not in the readings I assigned). His argument there might be summarized as follows:

1. Anything that is a deceiver thereby manifests weakness, malice, and imperfection. For a deceiver is in need of things that it has to acquire by deception, or it wills harm to those it deceives, or what have you. But God is supremely perfect, in need of nothing, perfectly good, and so on. So, God is not a deceiver. (Hence he is not like the “Evil Genius” of the First Meditation.)

2. Now, God created me (as Descartes thinks he has shown in the “preservation argument”), and that means he created my faculty of judgment, i.e. my capacity to form judgments or come to conclusions about what is true or false. But if God created me with a defective faculty of judgment, one that was basically unreliable, then he would be a deceiver. So, since he is not a deceiver, my faculty of judgment must be reliable.

3. That does not mean that I can never fall into error, because the possibility of error follows from my limitations as a created thing. But I can at least avoid error in practice if I try.

4. Error actually occurs when my will overreaches my intellect and makes a judgment about what is true or false in the absence of a “clear and distinct perception” of something’s being true or false. For if something strikes me clearly and distinctly to be correct (such as “I think, therefore I am,” or “1 + 1 = 2,” or “All men are mortal and Socrates is a man, therefore Socrates is mortal”), then God would be a deceiver if even these clear and distinct perceptions were in error. Since, again, he is no deceiver, then I must be able to trust whatever I clearly and distinctly perceive to be the case. Those judgments must be reliable.

5. I can avoid all error, then, if I refrain from drawing any conclusions except where I have a clear and distinct perception of the truth of some claim or the validity of some argument.

Clear and distinct perception

The idea, then, seems to be that as long as we start with “clearly and distinctly” self-evident truths (like the Cogito, basic mathematical truths, etc.) and carefully reason from them via “clearly and distinctly” valid chains of argumentation, then we can arrive at all kinds of further truths and won’t be led into error. This is the way Descartes wants to carry out the rationalist project of rigorously reconstructing all knowledge on a foundation of undoubtable truths.

The reality of the physical world

This raises many questions, such as exactly how we should understand the idea of a “clear and distinct perception.” But for now let’s see how Descartes uses all of this to show that the physical world external to the mind is real after all – that we’re not just dreaming it, or being caused to hallucinate by the Evil Genius. He address the issue in the Sixth of his Meditations. The reasoning basically goes like this:

1. I find within myself a passive tendency to have experiences of physical things. For example, even if I doubt whether the chair I am sitting in or the window I am looking out are real (as opposed to mere dreams or hallucinations) I can’t help but have the experiences of these things, as if they were real.

2. Something must be actively producing these experiences in me.

3. But I can’t be the one producing them, because I have no control over them; so it must be something outside of me that is causing them.

4. Now, there are three possible outside sources of these experiences: either there really are physical objects outside me that are causing me to have experiences of them; or God himself is causing me to have those experiences; or perhaps some non-material being other than God (such as the Evil Genius) is causing them.

5. But I have a very strong built-in or natural tendency to believe that it is real physical objects outside me that are causing my experiences of them, and God made me with that natural tendency.

6. So, if in reality it was something else causing those experiences – such as God or the Evil Genius – then God would be deceiving me, because he would have made me with a natural tendency to believe falsehoods.

7. But (as Descartes argued earlier) God is not a deceiver.

8. So my experiences really are caused by a world of physical objects outside me, so that the physical world is real and not a mere dream or hallucination.

Hey, I’m not in the Matrix anymore!

Rationalism defended

So, Descartes thinks we can know, after all, that we are not dreaming and that there is no Evil Genius. To that extent, he defends common sense. But he does so in a non-commonsensical way. Common sense would say that the senses provide certain knowledge, and perhaps the starting point of all knowledge. It would say that what we know first and best is the world of physical things, and that if we are going to know about any non-material realities (such as God and the soul), we are going to have to reason to them based on what we know from experience.

As we have seen, philosophers like Aristotle and Aquinas agree with that. They think that we can prove the existence of God and the immateriality of the mind, but they appeal to starting points in sensory experience of the physical world.

But Descartes does not agree. He thinks that what we know first and best is the soul (the self that thinks “I think, therefore I am,” which, as we’ll see, Descartes takes to be non-material) and God. Only after we establish the soul and God can we go on to establish the existence of the physical world. And we don’t start with sensory experience either. Rather, we start with things we can know apart from sensory experience (such as the Cogito, and God’s existence), and then justify sensory experience itself by reference to these things.

So, Descartes is reconstructing human knowledge according to rationalism, the view in epistemology or theory of knowledge that, as we have seen, he favors. We will see next how he also has a distinctive position in metaphysics – namely, Cartesian dualism, which differs from Aristotle’s and Aquinas’s version of dualism, just as his approach to epistemology differs from theirs.

Here are some optional YouTube video on different approaches to answering skepticism about the existence of the physical world, including Descartes’ approach:

Daniel Bonevac on Descartes’s Cogito:

https://www.youtube.com/watch?app=desktop&v=SM8VyazzXwo

Wireless Philosophy on Three Responses to Skepticism:

https://www.youtube.com/watch?v=xehTcQeqDWs