Tuesday, May 8, 2012

Locke's distinction between primary and secondary qualities

To: Christian M.
From: Geoffrey Klempner
Subject: Locke's distinction between primary and secondary qualities
Date: 20 August 2007 13:24

Dear Christian,

Thank you for your email of 10 August, with your University of London essay written under examination conditions, 'Does the notion of resemblance enable Locke to successfully distinguish between "mere powers" (secondary qualities) and "real qualities" (primary qualities)?'

This is a good essay. There are a couple of points I want to raise which you do not discuss, concerning the limitations of Lockean/ Cartesian 'physics' in accounting for the property of mass, and, more radically, contemporary views about the nature of the ultimate physical constituents of reality.

But more of that in a minute.

You offer two main difficulties for Locke's account. the first concerns Berkeley's claim that all qualities are, in effect, secondary qualities, so that the very notion of a 'primary quality' is incoherent. A point you could have made is that this criticism follows from Berkeley's rejection of the notion of 'material substance', in other words his metaphysics of 'immaterialism'.

Berkeley's critique is 'difficult to refute' only insofar as immaterialism is difficult to refute. (I disagree with commentators who think that the theory of immaterialism can be undermined by pointing to alleged fallacies in Berkeley's reasoning. See John Foster 'The Case for Idealism' and Timothy Sprigge 'The Vindication of Absolute Idealism' for contemporary defences of idealism.)

However, your response to Berkeley is correct if we take Berkeley's criticisms out of the context of immaterialism and consider them on their own merit. I agree that, as such, they depend upon 'too strict' a notion of representation.

However, I puzzled at first over your second argument:
Secondly, the fact that Locke uses resemblance to express his intuition that primary qualities are really in the objects is a logical contradiction. Resemblance implies that there is a certain abstraction That A resembles B requires that A and B are not identical but similar with respect [to] certain criteria that both fulfil. But if primary qualities, like a shape, of an object is similar to what is its representation, then there need to be the possibility of a higher level of abstraction. But for a simple idea how should we be able to form a more general term for it (simple ideas are elementary, non definable sense experiences [according to Locke]).'
One possible worry is that we compare A and B with a template C, and say that A resembles B insofar as they both match C. This looks like a version of Plato's 'one over many' argument for his theory of Forms. In addition to my oblong perception and the oblong telephone box which I perceive, there must exist The Oblong, or the Form of Oblong. This is vulnerable to the objection that if the Form of Oblong 'resembles' the telephone box or my perception of the telephone box, then there arises a second Form, leading to a vicious regress (the so-called 'Third Man Argument').

Your point seems to be that we have to distinguish between the perception of the telephone box, which is a complex idea, and its constituent simple ideas, one of which is the idea of extension as such. The problem is that the idea of extension is not actually extended because it does not exist in space, whereas an extended object is extended. In that case, what could the two have in common, in order to provide a basis for resemblance, which is neither actually extended nor actually unextended?

However, there is something in common between the actually extended object and the unextended idea, namely, that they both obey the laws of geometry. Being subject to the laws of geometry would be the common property.

I said I would get back to the point about the property of mass, and contemporary views about the ultimate nature of matter.

One of the most compelling criticisms which Leibniz makes of Cartesian physics is that mass - which gives rise to the properties of impenetrability and inertia - cannot be derived from the geometrical properties of an object. These are qualities which are not given to vision but only to an agent manipulating physical objects in an environment. Locke's theory can be criticized insofar as it fails to appreciate this point.

Contemporary physics has begun to break down the idea that the ultimate constituents of matter have spatial properties. Locke assumed the theory of the day - the Newtonian theory of 'corpuscles'. He even speculates at one point about what it would be like to possesses the 'minute' senses of angels, able to perceive the ultimate material constituents of an object. So it is a valid question to ask, to what extent the primary/ secondary quality distinction can be defended given these developments.

You do well, in attempting to give an alternative account of the primary/ secondary quality distinction. A fuller explanation would have to consider the question of what, if any, of the qualities that we are able to perceive are necessarily required by physics, apart from the property of number. The answer seems to be, at the present state of scientific knowledge, 'we can't say for sure.'

All the best,