Philosophy

5

LECTURE: Descartes on knowledge and skepticism

Let’s turn to Descartes’ First Meditation, and see how he there begins to carry out his project of radically reconstructing human knowledge on a rationalist (as opposed to either an Aristotelian or an empiricist) foundation.

The “method of doubt”

Commentators often describe the method Descartes uses in the First Meditation as the “method of doubt.” The basic idea can be understood by way of an analogy. Suppose you are looking for a needle in a haystack. The needle is so small and the stack so big that if you try to look directly for it, you’re likely to miss it. But suppose instead you look for all the non-needles – every piece of hay – and put them aside. This would be tedious, but when you were done finding all the non-needles, then what you would be left with would, of course, be the needle.

Now, Descartes wants to know what is certain – what cannot possibly be doubted – but to do that, he first looks for what is not certain, what is doubtable. And the idea is that, whatever he finds is left over after finding out everything that is doubtable or uncertain will be the certainty, the truths that are impossible to doubt, that he is after (just as you can find the needle by first focusing on the non-needles).

Another analogy would be to think of putting up a new, solid, earthquake-proof building where an old, unstable, and earthquake-damaged building stands. Ultimately you want to build, but first you have to destroy – to tear down the existing structure in order to clear the way for the new one.

Similarly, Descartes wants to tear down rival systems of thought (in particular, Aristotelianism and empiricism), and so he first emphasizes what is uncertain, as a way of casting doubt on these systems and tearing them down. But he ultimately wants in this way to find out what is certain or undoubtable, and use that to put up his own new “building” or structure of knowledge.

The “method of doubt,” then, is basically this:

1. For every belief, ask yourself if there are any grounds for doubting it (even far-fetched grounds – he wants to find absolute certainty, and thus to put aside, for the purposes of the method, even things where doubt might seem extreme).

2. Put aside anything that can be doubted, even if only in theory or in a far-fetched way.

3. Use what is left over after this exercise – that is, what is certain and cannot be doubted – as the foundation on which to reconstruct all knowledge.

The dream argument

In the First Meditation, Descartes applies this method, and makes use of a series of odd thought experiments that have became famous (or maybe “notorious” is the better word!) We’ll focus on just two of them.

The first is often called “the dream argument,” and it basically goes like this:

1. The beliefs I have at any given moment about the ordinary physical objects I take to exist around me are based on sensory experience – on what I seem to be seeing, hearing, tasting, touching, and smelling.

2. Now, when I dream, I have experiences like this, but in that case what the experiences are telling me is false – the things I dream are not real.

3. But there is nothing in any experience I am having right now, or at any other moment, that can tell me for sure whether it is a waking experience or only a dream – even the most vivid experience (for example, one in which I tell myself “If only this were a bad dream!”) can turn out to be a dream.

4. And in that case, all the beliefs I have about ordinary physical objects could in theory be false, because they might in theory all be based on a dream.

5. And in that case, none of the beliefs I have about ordinary physical objects can be the rock-solid certain foundation of knowledge; I have to look somewhere else for that.

Now, people sometimes misunderstand this argument. They think Descartes is trying to convince us that we really might in fact be dreaming right now. No, he isn’t doing that. As we’ll see later, he thinks we can know for certain that we aren’t dreaming. What he’s trying to do instead is to show that the senses by themselves cannot show that we are awake and not dreaming, and therefore the senses cannot be the ultimate foundation of knowledge.

In other words, he’s trying to undermine the view of Aristotelians and empiricists alike that all knowledge is based on the senses. He wants to show that the senses themselves can be trusted only if they can be validated by something else, something knowable through pure reason, apart from the senses. He’s arguing for rationalism and innate ideas. And he’s looking for what is certain and undoubtable, and concluding that the senses don’t provide it – they aren’t the needle in the haystack, so we need to keep looking.

The Evil Genius

This idea is reinforced by another, and even weirder, thought experiment. We take it for granted that we have bodies that exist within, and interact with, a larger world of physical objects. And, again, we believe this based on what our senses tell us.

But Descartes asks: What if, instead, you are really a disembodied spirit, and there is no physical world at all? What if the reason you think otherwise is that you are hallucinating? And what if the cause of your hallucination is an all-powerful evil spirit or demon (what has come to be called Descartes’s “evil genius”)? Maybe all that exists is you, as a disembodied soul, and this demon, and the demon is causing you to hallucinate everything else! (The basic idea of the movie The Matrix goes back to this thought experiment from Descartes.)

No, not that evil genius…

Suppose you think you’ve got some evidence or solid argument that shows that there is no such demon. How do you know that that is not also itself just another part of the illusion that the demon is creating? It seems that anything you might point to as a reason to believe that there is no Evil Genius could itself be part of the hallucination. And so we have another argument for radical doubt, the “evil genius argument,” which we can summarize as follows:

1. It is possible in theory that there is a supremely powerful and clever evil spirit who, seeking to deceive me, is the true source of all the beliefs I have about the external material world, and even about my own body.

2. So all my beliefs about these things might be false, and therefore they too cannot serve as the rock-solid certain foundation of knowledge.

Here too it is important not to misunderstand what Descartes is up to. He is not trying to convince you that there really is an Evil Genius. He is not even claiming that, at the end of the day, we should take the idea seriously. As we’ll see later, he doesn’t think we should, and he thinks we can in fact know for certain that there is no Evil Genius.

What the argument is meant to show, instead, is this: the senses, and what we believe about the physical world, cannot be what gives us the foundation or starting point of knowledge. They are not the needle in the haystack that he is looking for. We need to keep looking, and to look for something we could know for certain even if we were dreaming, and even if we were being deceived by an Evil Genius.

The Cogito

It is in the Second Meditation that Descartes thinks he discovers this foundation. This brings us to Descartes’ famous “Cogito” argument. Here it is (drum roll, please):

Cogito, ergo sum (which is Latin for “I think, therefore I am”)

This, Descartes says, is, at last, something that is certain and cannot be doubted. It is that needle in the haystack of doubtable beliefs that he has been searching through, and the rock-solid foundation on which he can reconstruct all knowledge.

The idea is this. Suppose you are dreaming right now, even though it seems that you are awake. You would be thinking you are awake even though you are not. Still, if you are thinking, then you must exist in order to do the thinking. A non-existent thing cannot dream or have thoughts of any other kind.

Or suppose that there really is an Evil Genius causing you to hallucinate. Suppose that you are really just a disembodied spirit, and that your body and the entire rest of the physical world is just an illusion. Still, you must exist in order to be deceived by the Evil Genius. He cannot deceive a non-existent thing. If he’s putting false thoughts into your mind, then you must exist as a mind in order for there to be something to put false thoughts into.

Even if you are having false thoughts, then, you are having thoughts. You are thinking. And if you are thinking, you must exist in order to do the thinking. So, “I think, therefore I am” is, Descartes concludes, something you can know with unshakeable certainty.

That is one function that the “Cogito” argument serves in Descartes’ system: to serve as a new foundation of knowledge. And notice that it is something you know apart from the senses and via pure reason. For you can know it even if your senses are deceiving you.

Another function of the “Cogito,” as we’ll see later on, is to reveal the true nature of the “I” or self that does the thinking in question. And what the self is – what you are – is, in Descartes’ view, a thing whose nature is to think, a thinking substance.

As opposed to what? As opposed to the answer an Aristotle or an Aquinas would give. They would say that what you are, your essence, is to be a rational animal. But the “animal” part drops out, for Descartes. The reason is that if you could, in theory, exist without any body – as in the Evil Genius scenario, where you exist as a disembodied spirit – then the body, the animal side of you, must not really be a part of your nature or essence after all. Your true nature must be nothing more than pure thought.

We’ll come back to that a little later on. First, we want to see, next time, how Descartes moves on from the Cogito to reconstruct the rest of human knowledge. Arguments like the dream argument and the Evil Genius argument might, taken out of context, make Descartes seem like he is advocating a radical skepticism – the view that no knowledge is possible. But as the Cogito shows, that is not the case. Descartes is not a skeptic. He thinks we can know a lot and that we can know it with certainty. But he thinks that the way knowledge works is different from what Aristotelians and empiricists suppose.

Some optional YouTube videos:

Wireless Philosophy on The Problem of Skepticism:

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

Wireless Philosophy on Descartes’ Cogito Argument:

https://www.youtube.com/watch?v=7iGjiSbEp9c

Philosophy Classroom on Descartes' First Meditation: 10 key points:

https://www.youtube.com/watch?v=pGd3ofLSLVk