28 September 2010

Mild vs Radical Scepticism & The Dream Argument

Something important that came up in the last post was that there are two general kinds of scepticism: mild and radical. It’s best that I get this straight now before I continue confusing myself with the imprecise use of terms like know, know that I know, certainty, absolute certainty and justified belief.

In Scruton’s wording…

Mild scepticism: our grounds for belief do not prove the beliefs conclusively.

Radical scepticism: our grounds for belief do not justify them at all.

Radical scepticism is the serious challenge, and this is what Descartes sets out in the Meditations. At least, this is the best (most challenging) way of interpreting Descartes.

In the above definitions I haven’t mentioned knowledge. Knowledge is justified true belief, so even if we have a justified belief, we can only know that we know it if we can prove the belief. But very often, indeed most of the time, we cannot do this. If scepticism consisted only in pointing out that we cannot prove our beliefs, that is, that we cannot prove that our beliefs amount to knowledge (this is mild scepticism) then we could cope with it, because we do not expect to be able to prove everything – even, or especially, our most basic beliefs about the existence of an external world or of other minds.

But radical scepticism not only questions our knowledge: it attacks the justifications of our beliefs, claiming that they are not adequate justification – they are not sufficient grounds – at all. We do not really need to worry about knowledge here at all: things are bad enough already.

Incidentally, it occurs to me that mild scepticism cannot be defeated at all, because it is always a logical possibility that if you are well-justified, via empirical evidence, in believing that P, it is yet the case that not-P. From this I conclude that attempting to “defeat” scepticism of this sort is the wrong approach. What it tells us is just that we need more and better justifications.

(Does that mean that the foundations of all knowledge are weak, or just that they are mostly invisible?)

The Dream Argument

A reminder of where Descartes is coming from is in order:

Reason now leads me to think that I should hold back my assent from opinions which are not completely certain and indubitable just as carefully as I do from those which are patently false. So, for the purpose of rejecting all my opinions, it will be enough if I find in each of them at least some reason for doubt.

Then he goes on to observe that his beliefs are based on his sensory experience:

Whatever I have up till now accepted as most true I have acquired either from the senses or through the senses. But from time to time I have found that the senses deceive, and it is prudent never to trust completely those who have deceived us even once.

Now for the bit about dreaming. To begin with Descartes says he cannot doubt that…

I am here, sitting by the fire, wearing a winter dressing-gown, holding a piece of paper in my hands…


How often, asleep at night, am I convinced of just such familiar events — that I am here in my dressing gown, sitting by the fire —when in fact I am lying undressed in bed!


As I think about this more carefully, I see plainly that there are never any sure signs by means of which being awake can be distinguished from being asleep.

Here is another version of the argument as I presented it in my post on Moore’s here is a hand proof., substituting hands for dressing gowns:

(P1) If I cannot tell the difference between waking and dreaming, then I am not justified in believing that there are two hands in front of me

(P2) I cannot tell the difference between waking and dreaming

∴ I am not justified in believing that there are two hands in front of me

This is radical scepticism. It is not just that I cannot prove my belief (that I have hands in front of me); it is that the experience of seeing my hands is no ground at all for the belief! Having the experience of seeing the hands is quite compatible with there being no hands in front of me (because I am dreaming).

Let’s look again at how Moore’s argument stands up to this. (P2) is replaced with a denial of the consequent of the material implication of p1. In other words, Moore’s new (P2) is “I am justified in believing that there are two hands in front of me.” This is inconclusive, because the sceptical premise, that we cannot tell the difference between waking and dreaming, also seems to have a lot going for it. That is, it seems to have as much going for it as the premise that “I am justified in believing that there are two hands in front of me.” If we employ inference to the best explanation for the experience of having two hands in front of me, then actually having two hands in front of me does seem like a good explanation. But both versions of (P2) seem reasonable, and the sceptical upshot is that beliefs either way are not sufficiently grounded – but it is enough for the sceptic that I am not justified in rejecting his (P2), because then I cannot deny the sceptical conclusion. In the end, then, Moore’s argument is a dismissal of the sceptic, rather than an answer to him.

Does this mean that when Moore claims that it does not matter that he has not faced up to scepticism (he claims that his proof still stands) it is only because he is thinking of mild scepticism? I think so, because from the radical sceptical standpoint – our grounds for belief do not justify them at all – Moore’s premise is not justified.

But what does Descartes himself say? He senses that the dream argument doesn’t have the devastating power it needs to cast him into doubt about everything.

Perhaps, indeed, I do not even have such hands or such a body at all. Nonetheless, it must surely be admitted that the visions which come in sleep are like paintings, which must have been fashioned in the likeness of things that are real, and hence that at least these general kinds of things – eyes, head, hands and the body as a whole – are things which are not imaginary but are real and exist.

However, painters can paint all kinds of fantasy creatures, and in the same way the forms that dream visions take could still be imaginary; we can continue to doubt that hands and heads and eyes are real. But doesn’t the painter compose these fantasies from real elements, namely colours and shapes? The equivalent elements composing the dream visions are such things as space and quantity, and Descartes thinks that here, in geometry and arithmetic, he has found certainty: he cannot doubt that 2 + 3 = 5 or that a square has four sides.

The ideas that make up Descartes’ dreams seem to come from somewhere, so, as Scruton says, “he is entitled to suppose that he lives in a world which has the power to produce those ideas.” To doubt the realities of space and quantity requires more than the dream hypothesis can manage, hence he moves on to the more damaging demon hypothesis.

To me, a more natural way of stating this is that it is just in the nature of dreaming that we dream about real things. That is what dreaming means. What Descartes is doing when he arrives at the certainties of mathematics is reaching the point at which dreaming is revealed to be inadequate as a sceptical hypothesis.

Thus, although the dream argument, as formulated above, does look to be unanswerable, it still looks suspect because of the use made of the very concept of dreaming. It presupposes the difference between waking and sleeping, and therefore all the things Descartes has tried to doubt.

But what if, anyway, one of the premisses is wrong? I cannot, right now, see a way of calling the first premise into question, but how about (P2)? I do find it difficult to doubt that I am awake. I feel like I really can tell the difference. I remember waking up this morning and I remember everything I have done since; the events were normal and consistent, not like a dream at all. As we all know, the visions and narratives in dreams are distorted and unstable. So I can tell the difference between waking and dreaming, and (P2) is wrong!

Well, not really. Just because I can think about the phenomenon of dreaming and identify its unique aspects based on my memory and what I know from psychology, I cannot tell the difference, in my own experience, at any particular time. For all I know I could be dreaming now, and these memories could be dream-memories. However, these concerns do make the dream hypothesis problematic, or at least over-complicated.

Descartes requires a purer sceptical hypothesis for the purpose of demolishing his beliefs, and that is the essential reason that he needs to progress to the malicious demon.

Soon I hope to consider some other responses to the dream argument, such as those of Stroud and Wright.

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