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Primary and secondary qualities and Descartes' case for doubt


To: Anthony L.
From: Geoffrey Klempner
Subject: Primary and secondary qualities and Descartes' case for doubt
Date: 5 March 2007 12:49

Dear Tony,

Thank you for your two emails of 27 February, one resubmitting your essay which you originally tried to send in January, in response to the University of London Modern Philosophy question, ''There is no defensible distinction between primary and secondary qualities'. Explain and discuss,' and the other in response to the UoL Modern Philosophy question, 'What reasons does Descartes give four doubting all his former beliefs? Are they good reasons?'

Primary and secondary qualities

This is a hoary old question which you've had a good go at. You've managed to say most of the things that need to be said. However, there are two issues which you could have given more thought to.

The question is, 'there is no defensible distinction between primary and secondary qualities'. This should tell you something. You are not being asked specifically to examine the views of Locke and Boyle - which would be a perfectly good exam question - but rather make a judgement whether ANY distinction between primary and secondary qualities can be made to work, obviously with reference to Locke and Boyle, but also anything else that might be relevant.

Let's first look at Locke's view. Somewhere in the Essay, Locke remarks that if we had the sense organs of angels we would see the corpuscles of which all matter is composed. (Unfortunately, I have tried fruitlessly to locate the reference, after quoting this to another student who tackled this topic!)

If one were to ask, 'How do angels perceive?' obviously the mechanism is not going to involve the standard story of corpuscles interacting with corpuscles. However, Locke doesn't have to say. Tactile perception would do. Or maybe angels are simply not part of the order of nature. You are right, however, to emphasise that modern science has moved away from this view. The question, however, is what are the consequences for the primary/ secondary qualities distinction? In what sense, if any, does modern science vindicate Locke?

We can ask whether Locke's 'angelic' view is coherent. Is it logically possible that the universe might have been as described by the corpuscular theory? is there anything intrinsically wrong with the corpuscular hypothesis? I don't think there is. It is just false.

However, Locke is clearly wrong if he thinks that this is the ONLY basis on which the primary/ secondary qualities distinction can be drawn.

The next question, therefore, is how one can make this distinction without assuming the corpuscular theory. Is there a way to describe the difference between primary and secondary qualities which encompasses both Locke and modern physics?

In your last section you get close to it but I think you miss the essential point. Let's look at how one would define a typical secondary quality and a typical primary quality.

'An object is yellow if and only if it appears yellow to normal perceivers in normal lighting.'

This, I would claim, is the typical form of a definition of a secondary quality. What is notable is that the term being defined occurs on both sides of the biconditional. To 'appear yellow', subjects must be able to express the judgement, that 'x is yellow'. Agreement in judgements over what is yellow is the condition for the possibility (to express this in pseudo-Kantian terms) of there being objects which are yellow.

'A shape is square if and only if it has four equal sides and one right angle.'

In other words, 'square' is definable in terms which do not use the term 'square' while 'yellow' is not definable in terms which do not use the term 'yellow'.

Drawing the contrast in this way, paradoxically seems the reverse of the Lockean explanation. Locke would say that an object looks square because it IS square, whereas an object looks yellow because XYZ, where 'XYZ' is an explanation couched in terms of the corpuscular theory (or indeed modern physics) which does not mention 'yellow'.

An explanation of why these two ways of drawing the distinction are not inconsistent but in fact perfectly harmonious would be useful. I leave that for you.

Cartesian doubt

The question is what are the reasons Descartes gives for doubting all his former beliefs and are they good reasons, and NOT, what is Descartes' motivation four doubting all his former beliefs and is this motivation soundly based.

It is therefore strictly irrelevant to the question asked whether foundationalism is a good idea, what are the prospects of building the edifice of knowledge from scratch and so on. In an examination, with limited time, you would be better of giving a quick nod to Descartes' motivations, showing the examiner that you are aware that this is not the question being asked. You will lose marks as well as time if you answer a different question from the one being asked.

(Having said that, I can see that 'reasons for doubting all his former beliefs' might be seen as ambiguous. Arguably, it can either mean, 'reasons why all his former beliefs should be doubted', or 'reasons for attempting to put all his former beliefs in doubt'. In the latter case, your remarks about foundationalism would be relevant. Provided that you make it clear that you see an ambiguity in the question, you could get away with including those remarks.)

Essentially, we are looking at Descartes the sceptic and asking how good his sceptical arguments are.

The first thing to note is that 'all his former beliefs' covers a significantly wider range than modern scepticism of the 'evil scientist' variety. Descartes is prepared to be sceptical about the theorems of geometry or truths of arithmetic, he is even prepared to question whether there is such a thing as space.

You say, 'Descartes sometimes seems to be saying that it could be that all his beliefs are false (i.e. he might have no true beliefs at all), and at other times seems only to be saying that any one of his beliefs taken at random might be false. The latter is the conclusion that he eventually comes to, but this would still mean that no belief is indubitable.'

I puzzled over this. 'Some of my beliefs might be false but I don't know which ones' is consistent with most of my beliefs being true. Surely, on this basis I know a great deal which can be expressed in general terms. This is nowhere near sufficient for Descartes' purposes. On the other hand, 'all my beliefs might be false', is close to incoherence, if we consider that most people have 'omega inconsistent' beliefs, i.e. a set of beliefs which contain an unidentified inconsistency.

One could give a lot more space to consideration of mental disorder. At least while we are still in the first Meditation, it is a bit of a mystery why Descartes does not pursue this further. The reason is that it threatens the foundation of his epistemological theory, the notion of clear and distinct ideas. If I am suffering from full-blown paranoid delusions, then any 'evidence' which comes in will be reinterpreted in a way to save the theory. If I can't count on my own rationality, then there really is no way forward from that point.

When Descartes considers the possibility that an evil demon could deceive him even with respect to elementary arithmetical statements, one might well wonder whether we are still in the 'deception' scenario rather than the 'irrational' scenario.

Arguably, all the weight of Descartes' argument falls back on the evil demon scenario.

One needs to distinguish the 'evil demon' and 'evil scientist' hypotheses. With the evil demon, in effect, Descartes is saying that idealism of a Berkeleian variety MIGHT, for all he knows, be true, OR there might exist 'material objects' in 'space', but he cannot tell which of these theories is true on the basis of his experience. But in that case, is he asking an empirical question? Or is Berkeley right in drawing the conclusion that the very notion of a 'material object in space' makes no sense at all?

Recent discussions in epistemology have focused on the 'evil scientist' or 'brain in a vat' scenario. Hilary Putnam objects, in my view unpersuasively, against the argument for scepticism based on the brain in a vat scenario, on the grounds that if I am a brain in a vat then given semantic 'externalism', I cannot have the concept of a 'brain' or a 'vat'. You can get some mileage out of this.

More generally, there is room for discussion about the validity of the general line of sceptical argument:

1) If I know that I am sitting at my desk then I know that it is not the case that XYZ (e.g. XYZ=I am a brain in a vat).

2) Therefore, if I don't know that XYZ then I don't know that I am sitting at my desk.

How persuasive is that inference? See, e.g. the article in the Internet Encyclopedia on 'Epistemic Closure Principles'

Finally, I don't follow your argument for 'iii) Beliefs about how things are in reality are only open to doubt if in some sorts of cases you decide to assume, on the basis of past experience, that once you’ve concluded your belief was wrong, nothing will happen to upset that conclusion.'

First, it is important that Descartes doesn't formulate his evil demon argument in the way that one might formulate an evil scientist argument. 'I might be being deceived by an evil scientist' has content for me because I can imagine what it would be to discover this. Of course my 'discovery' can be wrong, in fact the scenario of 'waking up in a vat' could be the cleverly induced illusion, and my beliefs about my former life largely true. The point is that because there can always be new evidence, the evidence I have up to the present point in time is never enough to settle once and for all which theory is correct, although it might incline me to one theory rather than the other.

The evil demon scenario, by contrast, is not a possibility that I can represent in terms of a possible future experience. Any possible future experience is fully consistent with the evil demon scenario and also with the commonsense materialist scenario.

All the best,