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Locke on primary and secondary qualities


To: Julian P.
From: Geoffrey Klempner
Subject: Locke on primary and secondary qualities
Date: 7 April 2006 13:29

Dear Julian,

Thank you for your two emails of 29 March, with your University of London essay in response to the question, 'Does Locke's Distinction of Primary and Secondary Qualities Survive Scrutiny?'.

I looked for the place where Locke imagines that angels would have the ability to 'perceive' corpuscles themselves. Rather than waste any more time on Google, I thought it would be best just to get on with this.

There seem to be two levels at which 'microscopical eyes' might operate. At one level, they would work in a manner analogous to human eyes, discerning the fine structures upon which much of the macroscopic properties of physical objects depend, but still requiring a yet finer structure to explain the mechanism of perception itself. But there is a deeper level at which one might hypothesize the ability to perceive the ultimate physical constitution of things - at least, so (I believe) Locke thought.

But what would this ultimate 'perception' be like? What we have discovered, through this thought experiment are really two separate questions:

1. Is Locke right to assume (as I believe he did, if I can find the right quote) that it is possible, in principle, for creatures sufficiently 'angelic' to 'perceive' the ultimate constituents of matter?

2. Why are secondary qualities needed anyway? Can we imagine a race of creatures who do not 'perceive' via 'sense organs' but rather by direct interaction with physical objects themselves?

The answer to question 1, I would argue, is, no. Locke is wrong. This is where Locke's account of primary qualities relates to his view about 'real essence' (at least on the sane, Mackiean interpretation). Locke's theory of knowledge depends upon the Cartesian idea that the essence of physical things - shape and extension - is given in perception. Modern physics shows that this assumption is false. Superstrings or quarks are theoretical posits whose behaviour we can model mathematically, but which bear no literal 'resemblance' to anything given in perception (except in the very slender sense that models of their behaviour involve geometrical concepts like 'next to' or 'around' or 'between' - maybe on the deepest level not even that.

You say, 'In the light of modern physics it is clear that Locke was trying to get his distinction of PQ and SQ to do two jobs. One is to distinguish between which qualities are "really" in objects, and the other is to form the set of qualities which are the minimum basis of a successful physical theory.' Could it be argued that once we have recognized that some of the properties required for a successful physical theory do not correspond to anything given in perception, the way is open for the possibility of a physical theory which would, in effect, show that all apparently 'primary' qualities are in fact secondary? Is that a coherent view? or does it require a Berkeleian idealism or Kantian phenomena/ noumena distinction? (in which case we are no longer talking physics but metaphysics).

Question 2. relates to Hume's point which you quote about inpenetrability. Leibniz famously clashed with Descartes over the 'essence' of physical objects. In the end, Leibniz was proved right. The nature of physical objects cannot be deduced from geometrical notions alone (arguably this is why Descartes was led to believe that mind-body interaction is possible).

I would argue that there could be intelligent creatures whose only immediate knowledge of their environment was through physical push and pull. This is indeed what physical (as opposed to metaphysical) 'angels' would be like. There is no way to 'see' a corpuscle but you can still 'push' it or 'feel' its surface texture. What this does require is 'proprioceptive feedback'. But there is no necessity that this be manifested in any other form than simply immediate knowledge of how one is moving one's body.

Suppose these creatures develop a technology. Then they could acquire artificial 'eyes', 'ears', etc. All without secondary qualities. (What I am envisioning is NOT Chalmers' 'zombies' or anything of that sort - these creatures have an inner life, it is just not a life which has any secondary qualities as constituents.)

I don't know if Locke himself believed in the 'necessity' for a primary/ secondary quality distinction in the sense that such a distinction would be an ineliminable part of a theory of knowledge for any creatures whatsoever. A theory of knowledge for 'physical angels' has no role for the distinction. He did, however, believe that it is necessary in another sense, namely, that there must be something given in perception which corresponds to the properties of physical objects themselves. What is required to challenge this assumption is either a metaphysical theory like Berkeley's according to which there is no such thing as 'physical' object in reality, or, possibly, a physical theory (maybe like Bohm's 'implicate order'?) which seeks to explain the very notion of 'spatial position' in terms of something more fundamental.

All the best,