Thursday, August 18, 2011

Descartes' argument for scepticism in the 1st Meditation

To: Andrew W.
From: Geoffrey Klempner
Subject: Descartes' argument for scepticism in the 1st Meditation
Date: 20 May 2004 10:32

Dear Andrew,

Thank you for your email of 13 May, with your University of London essay in response to the question, 'In his First Meditation how does Descartes attempt to show that there is reason to doubt everything one believes?'

You say in your email that you 'have not been ambitious... and have just tried to get to grips with the salient points of Descartes' First Meditation'.

A general comment on this. It is very difficult, if not impossible *merely* to get to grips with an argument. You are reading Descartes critically. That means looking for points where the coherence or validity of what Descartes says can be questioned. This exercise can be carried out even if you ultimately find yourself in full agreement. For example, you can raise objections, then answer them on Descartes' behalf. Or you can consider cases - 'counterexamples' - to which a general claim which Descartes makes does not seem to apply, then show how in fact it does apply when thought about more carefully.

Ostensibly, the question requires you to relate the different steps or stages of Descartes argument. Although the essay question doesn't actually say, 'Is the attempt successful?' this is something you must be asking yourself. It may be necessary (as we shall see below) to add something to what Descartes actually says, in order to show how the argument works, how, in his own eyes, Descartes feels he is justified in drawing the conclusion that there is 'reason to doubt everything one believes'.

You say in paragraph 1, 'he does not want merely to demonstrate that all his former opinions are false'. 'Merely' implies that Descartes is seeking to do more, whereas in fact he is seeking to do less. It will not be necessary to demonstrate the falsity of each of his former opinions, because he will question the assumptions on which these opinions are based. Nor is it the case that Descartes is seeking to prove that these general assumptions are false. Rather, he is seeking reasons for doubting them. The ultimate aim, as Descartes explains, is to discover a foundation for knowledge capable of withstanding these doubts.

The phrase, 'Through a series of taut, rigorously argued passages' can be omitted. It looks like waffle.

In the next paragraph you miss a step. After considering that the senses sometimes deceive us, Descartes counters that it is those very senses which are used to correct our perceptual judgements, as when we take a closer look at something. That is why a more general argument is needed questioning the trust we naturally place in our senses.

You relate how Descartes uses the God hypothesis to show how one might be deceived even about the simplest mathematical propositions. 'But Descartes knows that God does deceive us sometimes'. He doesn't say this. What he says is that God 'allows us to be deceived'. (Later in the Meditations, Descartes goes to considerable lengths to show how errors naturally arise through the malfunctioning of our bodies or sensory apparatus. When we are deceived, God does not deliberately deceive us, rather, the error is the result of a natural process of cause and effect and as such unavoidable. Any physical arrangement for gaining knowledge will lead to errors sometimes.)

When you discuss the 'final passages' where Descartes raises the spectre of the evil demon, you follow Descartes explanation, that the thought of an evil demon will help Descartes to persist with his doubt ('My habitual opinions keep coming back'). It seems, therefore, that the evil demon serves a merely psychological function. Is that right?

The question raised is about probability. Why can't Descartes say (as he is tempted to say) that although it is possible that his former opinions are false, it is more probable that they are true? Isn't this what we would say? 'Yes, it is possible that I am on a laboratory bench, having dreams fed to me by an evil scientist, but highly unlikely!'

It would gain you extra marks to do a bit of philosophy here. Think about what answer you would give to this.

The implied argument, which is not explicitly stated, is that if we grant the coherence of the evil demon hypothesis, then it is impossible to make a judgement of probability. It is impossible to say how probable or improbable it is that there exists an evil demon. Judgements of probability are based on prior evidence. E.g. we rate Jolly Roger's chances of winning the race at 5-4, on the basis of his form this year on the flat. If we'd never visited a race before, and didn't know the odds for the different horses in the race, then so far as we are in a position to judge, each horse has the same probability of winning. The same conclusion would follow if we were told by a reliable source that all the horses but one had been doped, so the form book was useless.

This, then, sets the task of *disproving* the evil demon hypothesis - i.e. showing that it has zero probability - which Descartes sets out to do by proving the existence of a benevolent God.

All the best,

Geoffrey