So let's move on now to another Cartesian topic, dualism.
This is certainly the view for which Descartes is now best known.
If you find the word Cartesian in a philosophical text, the most likely accompaniment is the word dualism.
Cartesian dualism is fairly straightforwardly stated.
He takes the body to be material made of matter whose essence is extension.
And he takes the mind to be made of a completely different substance, immaterial substance, nonmaterial whose essence is thinking.
So we've got two distinct substances. Now, that's very important.
Notice to be a Cartesian dualist.
It's not enough that you just think mind and body are different or even that mind and body have different properties.
You've got to think that there are different substances. And that is a very substantial claim.
Now, in the discourse on method, Descartes argues something like this, I can doubt that my body exists.
I cannot doubt that I exist. Therefore, I am not identical with my body.
Quite a tempting argument, at least to start with.
Put yourself in the position of the sceptic. What can I be sure of?
Well, the only thing I can be sure of is my own thoughts and my own perceptions.
So I'm absolutely certain that I exist. But when I contemplate my body, if it's all an illusion, I cannot be sure that my body exists.
Surely then my mind and my body must be distinct things.
For example, I can imagine myself transported maybe to an afterlife or something like that in which I don't have a body.
But I still think I can imagine myself in that situation.
So surely I and my body must be distinct things. It seems quite plausible, but actually, as it stands, this argument is fallacious.
So here's an example. Hesperus and Phosphorus are ancient names for Venus.
Phosphorus is the morning star. Hesperus the evening star.
The ancients didn't know that they were the same heavenly body. They are.
In fact, Venus, of course, is quite close to the sun hits between us and the sun.
So it only ever appears in the morning or the evening. Never in the middle of the night.
Okay, so imagine somebody who does not know that Hesperus and phosphorous are the same and they might present this argument.
I can doubt that Hesperus is phosphorous. Indeed, maybe I do doubt that Hesperus is phosphorous.
But I can't doubt that phosphorus is phosphorus. Therefore, Hesperus isn't phosphorus.
Because Hesperus and Phosphorus have different properties, okay? One of them I can doubt to be phosphorus.
The other one I can't out to be phosphorus. And there's no way that the same thing can have different properties.
So that's appealing to a room called Liden.
It's his law. In fact, life mixes. Law is used in different ways by different people.
But this is one particular form of it, if I can be of the same thing.
Then any property of a must also be A property of B. So if you have F.A.A., that means F is a property of A and A and B at the same F, B follows.
So if F is the property of being doubted by me to exist, A is me and B is my body.
We get Descartes argument from the discourse and by suitable substitution you can get the argument that I just put about Hesperus and phosphorus.
But you can see that this is fallacious.
If you put the problem, if you count as a property, something like being doubted by me to be to be prime minister, you can get.
I don't doubt that the prime minister is the prime minister. I doubt that Gordon Brown is the prime minister.
Therefore, Gordon Brown isn't the prime minister. Very easy to produce lots of examples of fallacies.
And the simplest way to avoid it is simply to highlight that being doubted by me to be something is not a genuine property of the object.
When I doubt whether Hesperus is phosphorous. My doubt is not a fact about that planet.
It's a fact about me. And it's about the fact that I am not aware that the appearance of this planet in the
morning is an appearance of the same planet that appeared in the evening some weeks ago.
It's not a fact about the planet so much as about me. So that argument of Descartes is well known to be fallacious.
But he produces a more interesting argument in the sixth meditation, which is certainly much better, but has questionable premises.
And it goes like this. When I contemplate myself, I can very clearly understand myself as being a thinking, non extended thing.
I can see, at any rate, that I'm definitely a thinking thing because here I am thinking.
So I'm obviously a thinking thing and I can have a clear understanding of what fault
is sufficient to enable me to see that I am potentially not an extended thing.
I also likewise have a clear understanding of body as extended and not thinking.
So when I contemplate a physical object, I'm aware that it is necessarily extended.
And I'm also aware that it is not essential to its being that it be a thinking thing.
Indeed, it seems hard to see how a physical extended body can be.
A thinking thing certainly doesn't seem to be essential to it be so.
Well, if I can clearly understand what it would be for me to be a thinking thing and not extended and for extended things not to be thinking, well,
in that case, it's possible for God to create a world in which these things that I'm clearly understanding as possibilities are actual truths.
And it follows that if God could create me as a thinking thing distinct from my body as an extended thing,
then they must indeed be genuinely distinct things. If they were not distinct, God would not even God would not be able to create them as separate.
Now, I've mentioned that you've got a very crude argument in the discourse in the meditation's, you've got a much more sophisticated argument.
But even in the meditation's, Descartes does try to make this move from doubt to knowledge of his essence.
So here's a quotation. What should I now say that I am when I might be deceived by an evil demon or dreaming?
At present, I'm not admitting anything except what is necessarily true.
I am then, in a strict sense, only a thing that thinks that is I'm a mind or intelligence or intellect or reason.
What kind of thing is that? A thinking thing? So notice what he's doing.
He's using his scepticism. Remember, he started out saying, I'm not going to accept anything except what he's completely certain.
He then points out that he is certain of his own thinking and his own existence and moves on to say, therefore, I can be sure of that.
But that's the only thing I can be sure of. I am a thinking thing.
But this is a dubious move to distinguish two different meanings of a thinking thing.
What do we mean when we say that a thinking thing? Well, we could just mean something that thinks or we could mean something.
Whose essence is to think? Something which is in its own essence, a thinking thing that cannot be anything else.
That cannot not think. And those are two very different claims and the kind of move that Descartes is making here from epistemology to metaphysics.
That is, he is arguing from how we come to know something to what it is that is in general a very suspicious move.
Knowing that, I am thinking it does follow that I am a thinking thing.
In one sense, if I am actually thinking, then I must be something whose which is capable of thinking,
at least if you don't put too much stress on the word thing.
But it doesn't at all follow that I'm something whose essence is to think.
So suppose, for example, I mentioned a couple of lectures ago about John Locke coming out with the speculation that God could make matter.
Think so. He imagined God took a stone and made it think the stone thinks to itself.
Ah, I know I'm a thinking thing. Even the stone only knows that it's a thinking thing.
It doesn't know it's an extended thing because it has the same problems as we do.
It's only aware of its own perceptions.
It could then conclude that it was something whose essence is to think and it would immediately be proved wrong.
When God withdrew from it, the power of thinking on the stone would still exist.
What about the final move of Descartes argument, this seems rather more defensible, though, on the face of it, it might seem dubious.
God could have created my mind and body as separate entities. Therefore, it is possible for my mind and body to exist separately.
Therefore, my mind and body are, in fact, distinct things.
Now, at first sight, this might seem to be committing exactly the same fallacy that I've just been talking about.
It might look as though something metaphysical a fact about what could be the actual
distinctness of two things is being inferred from what is just a hypothetical possibility.
Well, it's very important that the possibility be understood in the right way.
So let me give you an example. Suppose I look up in the sky one day and I see Hesperus, we could do later.
I look up and I see phosphorous. Maybe I don't know that anybody's even suggested that these are the same heavenly body.
Or maybe the thought occurs to me and I say to myself, well, it is possible for Hesperus to be snuffed out while phosphorous survives.
Maybe I'm thinking of some cosmic catastrophe. That's heavenly body.
Hesperus could meet with some accident while phosphorous survives.
So there's a real possibility of one of them existing without the other.
Therefore, they cannot be the same object.
No, actually, there's nothing wrong with that last move, but it depends on how you interpret possibility,
because actually when I speculate, it is possible for one of them to be snuffed out while the other survives.
Actually, you can respond to that by saying, no, it isn't possible. Unbeknown to you, it isn't possible because they are, in fact, the same object.
And if they are in fact, the same object, then it isn't possible for something to happen to Hesperus without it also happening to phosphorous.
But on the other hand, you might be inclined to say, well, surely the person in that situation contemplating these two object.
It is a real possibility. Yes, but only epistemologically when you say it is a real possibility that what one means is for all I know,
for all I know, one of the objects could meet with a calamity while the other one survives.
Yes, that's true. But that's a truth about my knowledge.
It's not actually true that one of those objects could really meet with a calamity while the other does not,
because they are, in fact the same object.
So, again, you have to be very careful when you talk about the properties of mind and body and so forth, or indeed heavenly bodies.
Are you actually talking about your knowledge of them or are you talking about their own properties, essences, cetera?
Hesperus and phosphorous are in fact the same object.
At least that's what we believe, because you might think, well, scientists could discover, you know,
next week that there's been some some great hoax and they're not actually the same object after all.
Yes, sure. For all we know, in a sense, that could happen.
But if they are the same object, in fact, then whatever happens to one of them must happen to the other.