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Descartes' argument for scepticism in First Meditation


To: Hakeem G.
From: Geoffrey Klempner
Subject: Descartes' argument for scepticism in First Meditation
Date: 6 December 2006 11:08

Dear Hakeem,

Thank you for your email of 29 November, with your second attempt at your University of London essay, 'What reasons does Descartes give for doubting all his former beliefs? Are they good reasons?

You have produced an excellent piece of work. You have made some very good points, and given clear evidence that you have thought hard about Descartes' argument in the First Meditation.

In particular, I very much liked the argument in paragraph 4: 'In other words, if senses deceive us with respect to the details of things around us they make available for our perception, can they be considered deceptive when they don't present us at all with the sensation of a present object when it is obstructed by another opaque object...'.

I also liked the discussion of dreams, and the point about 'contradictory realities'. In a well known article by the philosopher Anthony Quinton, 'Spaces and Times', the Cartesian thought experiment is taken a stage further. An individual goes to 'sleep' in one world and wakes up in another which is in every respect equally 'real', then returns to the first world by the same method. Would that be proof of the existence of two spatially unrelated spaces?

The only criticism I would make this time is that your essay is mainly an answer to the first part of the essay question, and not the second.

You do offer criticisms of Descartes' argument, as well as suggestions for improvement, and this can be taken as part of an assessment 'whether the reasons Descartes offers are good reasons'. However, a full answer to the question would have to include your own judgement whether, e.g., the evil demon argument IS a good argument. In other words, what is your view?

Do you think that it is logically possible that all your experiences are produced by an evil demon? And, further, if this possibility is granted, do you accept that it follows that you should doubt all your former beliefs?

There is nothing wrong, in principle, when faced with a question like this, with saying, 'Yes, I think they are good reasons.' In that case, the work you have to do for this part of the essay is in considering possible objections - objections which have been raised against, e.g. the evil demon argument - and the reply that you would give to these objections.

Let's look at each of these questions separately.

Do you accept that it is it possible that all your experiences are produced by an evil demon? One way to approach this would be to consider a more 'up to date' version of this argument, as provided by the film 'The Matrix'. What is the difference between an 'evil demon' hypothesis and a Matrix scenario? In the case of the evil demon, I am deceived into thinking that there is such a thing as 'objects in space', whereas in the Matrix scenario, the existence of objects in space is assumed in setting up the thought experiment. But is the idea that there could be a non-spatial reality consisting purely of experience coherent?

The second question is whether admitting this possibility is sufficient to put our beliefs in doubt. Common sense tells us that all sorts of things are 'possible' yet we don't for a minute allow these to cause us to entertain doubts. It is logically possible, for example, that the floor of my office will collapse in the next five seconds. But I'm not allowing myself to lose any time worrying about it! What is the difference between this case and the argument given by Descartes for doubting all his former beliefs?

Descartes would reply that in the case of my office floor, it is possible to rationally assign a probability, based on my general knowledge. Floor collapse without prior warning is something that very rarely happens in a well constructed house. However, probability is relative to evidence. In the case of the evil demon or Matrix scenarios, anything that might count as 'evidence' for a probability judgement is itself put into question.

Some philosophers e.g. Hilary Putnam have argued that even if we accept the coherence of the Matrix scenario (or 'brain in a vat', as Putnam describes it) this cannot be used as a premiss in a sceptical argument, because if I AM in a pod, or a vat, then I am not thinking real thoughts, my words do not have any real reference beyond my own mind. - You an explore this issue further for yourself. My own view is that this line is not ultimately effective against the sceptic.

Obviously, in an exam, you won't have time to write as much as you have written here. I'm telling you that you need to say even more! In a one hour exam, you have to explain yourself more briefly, while covering all the points you want to make. - Later on, you can practise some one hour essay questions.

There's no need to attempt this topic a third time. Try another essay topic, and this time paying particular attention to the exact wording. You have done very well this time.

All the best,