History of Philosophy in the 17th & 18th Centuries

Descartes 4

Descartes' proof of the External World

Let me remind you of the breathtaking follow-up to the proofs of God's existence:

'I do not see how God could be understood to be anything but a deceiver if these ideas [that sense gives us] were transmitted by a source other than corporeal things. It follows that corporeal things exist.'
Meditation 6.

We have explored Descartes' conception of 'mind' or 'a mind'. He puts forward the Cogito as saying that my mind exists. It shows 'I' exist (he thinks). And he explains that this can only mean that I as a thinking thing exist. Another way of saying this, for us anyway, is that I 'as a mind' exist.

So from the Cogito he has the conclusion that 'mind', or 'a mind' exists.

Mind or minds? Note 1

Having proved to his own satisfaction that God exists, Descartes then argues that if there is a God, the ordinary things around us must also exist.

Can you write in a sentence what this argument is?

Overhead 402

Can you suggest objections to this argument? Write one down.

Overhead 403

Overhead 404

Though these objections were put to Descartes, he was unmoved by them, and maintained the conclusions he had set out.

The Cogito proved the existence of mind or a mind, and the argument from that proved the existence first of God and via that of a populated external world.

The notion of a fundamental type of thing

This shows Descartes believing in two types of thing: thinking things, corporeal things - and maybe a third, God.

So here we have two types of thing, perhaps three.

Are there more?

Any other candidates for basic 'types of thing'? Note 3

It is this question of what 'basic' 'types of thing' that Descartes couches in terms of 'substance'. What substances are there?

Substance in Descartes

Descartes says that whatever is independent of everything else is a substance.

He says that strictly speaking there is just one substance, and that is God.

This has strong intuitive appeal. If you think there is a God, then you are likely to think everything else is wholly dependent on Him/Her.

Whatever Descartes means by saying that God is the one true substance, he goes on to make a distinction amongst the things S/He has created. Some of these he says are only dependent on God. They have no other dependence. But there are others which depend not only on God, but on other things as well. What Descartes has in mind here are what he calls 'properties'. For example, being striped. Being striped is a property of some things. If there weren't any striped things, there wouldn't be any being striped. So being striped is dependent on things, as well as on God.

So Descartes has in fact a hierarchy of reality:

Overhead 9

Descartes' hierarchy of reality

• God
• Things that depend only on God
• Things that depend on God but also on other things - properties.

He calls thing which are independent except for their dependence on God 'created substances'.

Those that 'need only the ordinary concurrence of God in order to exist' are properly called 'created substances'. Descartes, Principles, 25, see Cottingham p.177.

But mostly he calls them just substances. So his usual usage is to take it that a substance is that which doesn't depend on anything else for its existence (except God).

What substances are there?

For Descartes then one substance was God.

But what others were there?

You might think the answer is: lots. There are lots of things that are independent in the sense given. Lots of things that have properties but are not themselves properties (unless they are properties of God) : horses, clocks, boulders, lots of individual things.

But in fact it's not so straightforward:

Let's just take what we now call material things. Descartes thinks what you have with material things is not lots of substances but one substance - what he calls corporeal substance.

This shows that what I have said about substances is less helpful than it might have seemed. I said a substance according to Descartes is what depends on nothing apart from from God. And I tried to to explain this by contrasting a badger say with its being striped, a individual animal contrasted with a property of an individual animal.

But then Descartes goes and says that as far as material things are concerned there is just the one substance, 'body'.

He is grouping the badger not only with all other badgers, but also with everything else that isn't a mind and saying you've got one substance here, namely body.

It is body that has properties.

This needs a separate argument, which I don't have time to give here. An argument is needed, that is to say, to show that what we ordinarily think of as individual bodies - clocks, boulders, badgers and so on - are really just different stretches of 'body', or as we would probably put it, different stretches of 'matter'.

This is anyway what Descartes thinks. He thinks of the Universe as a continuum of corporeal substance.

Cartesian Corporeal substance contrasted with atomism (Cordemoy)

How does this picture of the universe, of a lump of dough, allow us to think of the things of ordinary experience? Descartes thinks there is local differentiated movement in the dough, and it is these that are the grounding of the things of our ordinary experience. This is the theory of 'vortices'. These local movements result in what are effectively particles, and particles of various sizes. (There are 3 main sizes.) This begins to suggest a kind of atomism, but Descartes' particles are all infinitely divisible. An atomic theory was developed by Cordemoy, who took inspiration from Descartes, but who differed from him in this respect. It was atomism, or corpuscularianism, which became the mainstream doctrine towards the end of the 17th Century.

See eg Cottingham's Descartes, Oxford, 1986, Blackwell, p.87.

Descartes' system has particles, but they are infinitely divisible.

Argument that the nature of corporeal substance is pure extension

What is the 'fundamental character' of corporeal substance?

Descartes thinks this is an intelligible question, and he gives an answer to it.

He argues that the essence of corporal substance is extension.

'Essence' and 'fundamental character' are fraught terms, but we shall begin to see what Descartes has in mind by considering his argument.

He basically asks us to think of a corporeal body with all the properties corporeal bodies have, and then to take each property in turn and ask ask whether a corporeal body would remain a corporeal body if it lost it.

He says all properties save one can be 'thought away' in such an experiment. E.g., you can imagine a corporeal body lacking weight, lacking colour, lacking smell,

Overhead 10

'weight, colour, and all other such qualities that are perceived by the senses as being in corporeal matter, can be removed from it, while the matter itself remains intact; it thus follows that its nature does not depend on any of these qualities.' Principles II 4.

Can you 'think away' the 'hardness' of a material object?

I.e., can you imagine a material body which offers no resistance when you move to touch it, or push it out of the way? He says Yes, arguing in the following way:

Suppose I go to touch a body and it takes itself off exactly as my hand moves up to it. I don't sense resistance or 'hardness'. But the body retains its nature. Therefore hardness cannot be part of that nature. Parallel arguments he says apply to all possible attributes of a body.

The only property that cannot be 'removed' from matter in this way is extension, and this therefore is its defining property.

Thus Descartes reaches the conclusion that the principle attribute of corporeal substance is extension.

Overhead 11

'The nature of matter, or body considered in general, consists not in its being something which is hard or heavy or coloured, or which affects the senses in any way, but simply in its being something which is extended in length, breadth and depth.' Principles I 4.

Descartes' corporeal substance is space.

This has the extraordinary implication that space is body.

The universe is a 'single, indefinitely modifiable, infinitely extended thing' for Descartes (C, p.85.) The idea of empty space is incoherent. What we may think of as a body of gas expanding, Descartes thinks of on the model of a sponge swelling with water. The sponge does not increase its extension in this process. Its pores simply draw in water from outside.

For Descartes matter is extension.

'[T]he nature of matter or of body ... does not consist of its being hard, or heavy, or coloured ... but solely in the fact that it is a substance extended in length, breadth, and depth.' Principles of Philosophy, 2.4.

Matter is therefore space:

'the extension constituting the nature of a body is exactly the same as that constituting the nature of a space.' Principles II 11.

'There is no difference between the extension of a space ... and the extension of a body. For body's being extended in length, breadth and depth in itself warrants the conclusion that it is a substance, since it is a complete contradiction that a particular extension should belong to nothing; and the same conclusion must be drawn with respect to a space that is supposed to be a vacuum, namely that since there is extension in it, there must necessarily be substance in it as well.' Principles II 16.
C p.86.

If corporeal substance is pure extension, it is to be studied by geometry

This conclusion (that matter is extension) allows Descartes to maintain that the study of matter is the province of geometry. Geometry is the science of extension, if you will.

And it is proper to look for the simplicity, precision and certainty which are the hallmarks of geometrical thinking in the study of matter too.

He thinks we arrive at this conclusion (that matter is pure extension) through a process of purely intellectual scrutiny, in which the sense play no role at all.

Since geometry is pursued by exercising the reason and not by experiment or observation, Descartes' conception of physics is profoundly rationalist.

(Locke - and Newton, and Boyle - rejected this element of Cartesianism.

Argument that 'a distinct understanding of wax' cannot be got through the senses - the piece of wax

Another indication of his rationalist, anti-empirical, philosophy is given in his discussion of how you discover the true nature of something. Take, he says, a piece of wax. It has a taste, a smell, a cloud, shape and size, noise when rapped.

'Let us take ... this piece of wax. It has just been taken from the honeycomb; it has not yet quite lost the taste of the honey; it retains some of the scent of the flowers from which it was gathered; its colour, shape and size are plain to see; it is hard, cold and can be handled without difficulty; if you rap it with your knuckle it makes a sound.' Meditation 2 Cottingham p.84.

But then imagine it melting. All these features disappear, and others take their place.

He concludes that 'a distinct understanding of wax' cannot be got through the senses.

If I remove all these features, all the properties that change and so cannot be part of the continuing identity of the wax, what am I left with? Simply the conception of something that is extended. A 3-dimensional object capable of taking on an indefinite number of shapes.

Mental Substance

So much for Descartes conception of corporeal substance, body.

The other substance he identified was mind, or minds. (Leaving out God.) We have talked about this a good deal already, so I won't say more here.

Let us just note that his recognition of just two 'types' of substance is the basis for calling him a dualist.

Dualism and its alternatives

Overhead 12

'There are two orders of reality or of existence: anything that exists or has some degree of reality - whether substance, attribute, or mode; whether created or uncreated; whether dependent or independent - exists either as a body, as part of corporeal, extended, reality, or as mind, as part of 'incorporeal' , 'spiritual', thinking reality.'

He never considers whether there might be more than two. He does consider that there might be fewer than two (unless you count God).

Materialism

He considered and rejected materialism., the view that the whole of reality is material.

Overhead 13

Hobbes: 'mind is nothing more than motion occurring in various parts of an organic body.'

Overhead 14

Mersenne: What if

'it turned out to be a body which, by its various motions and encounters, produces what we call thought? How do you demonstrate that a body is incapable of thinking, or that corporeal motions are not in fact thought? the whole system of your body, which you think you have excluded, or else some of its parts - for example those which make up the brain - may combine to produce the motions which we call thoughts.'

Descartes, see reference in Woolhouse, Descartes, Spinoza, Leibniz, London, 1993Routledge, p.21,2.

Idealism

The alternative monism is that all the modes Descartes thought belonged to the principle attribute of corporeal substance belonged in fact to thought. This is the view that Leibniz was to arrive at, and one which Berkeley (1685-1753) developed.

Review questions

1. Which best expresses Descartes' argument for the existence of the objective world?

2. Which best expresses Descartes concept of 'substance'?

3. How many corporeal substances are there, according to Descartes?

4. Which does Descartes defend?

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