Greg Detre
@ 11.30 on Thursday, 18 January, 2001
Lucy Allais, History of Philosophy I
Locke�s discussion of the distinction between primary and secondary qualities in matter, though he cannot really be credited with its invention, remains amongst his most contentious. It can be traced immediately back to a prototypical form in Descartes� formulation of the external world as being characterised essentially by extension. By �extension�, Descartes means that matter occupies space, having length and position, or size and shape � both pairs of qualities specify the quantifiable space taken up by objects relative to each other in a plenum. Over time, these primary qualities are sufficient to describe motion. To this list, we might want to add number, mass, charge and solidity, but we will not consider these here. Descartes specifies the qualities above as primary qualities because they are geometric, quantifiable and a priori (at least insofar as one cannot really imagine a person who does not hold these concepts, and this has relevance to both Aristotle and Bennett�s distinction). This objective Cartesian physical reality is a barren, colourless world, like monochrome blobs in a lava lamp, endlessly circulating within the boundaries of a primary-quality-only plenum. When we abandon the colours and textures of our phenomenological world, this is what is left � simply a four-dimensional space-time continuum.
For the most part, Locke, Descartes, Aristotle and Bennett agree in categorising such qualities (except maybe solidity) separately from secondary qualities, such as colour, sound, temperature, texture, flavour and smell.
The first justification Locke makes for this distinction is that the primary qualities are �utterly inseparable from the Body, in what estate soever it be; such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps... and the Mind finds inseparable from every particle of Matter�. This can be seen as similar to Descartes� analysis of how our conception of the melting wax is constant even as its secondary qualities alter. This is often cited as the distinction from science, and indeed Mackie highlights its usefulness to physicists right up until the development of quantum theory.
Another way of seeing this distinction is to ask: �Can I imagine a given quality divorced from its instantiation in an object?� For instance, one can easily imagine the colour indigo, or the smell of smoke, even without any indigo smoke wafting around in the room. On the other hand, it is perhaps impossible to imagine size or motion independent of an object of that size or moving in that way. This may be linked to Aristotle�s point that all of the secondary qualities are apparent to only one of our senses (�special sensibles�), while primary qualities can be viewed using two or more senses (�common sensibles�), usually sight and touch. It could be that the reason we cannot imagine primary qualities independent of an object is that we can conjure up a single vague sense impression, such as a sense of colour, but we cannot employ two insubstantial sense impressions without pinning down an object as their origin.
Locke also uses an argument of inseparability. If we cut up an object into increasingly small pieces, it loses its associated secondary qualities, but appears to retain its primary qualities. Mackie appropriately highlights the circularity of this argument, since it rests on our preconception that the primary qualities are primary.
Locke�s strongest argument for a distinction per se points to the feelings of pain or nausea that certain objects arouse in us, even though the pain and nausea do not appear to resemble the objects at all. In this way, it is only a small step to imagine that other qualities which the objects give rise to in our perceptions are similarly divorceable. However, such a view effectively commits Locke to some form to the representative theory of perception, which suffers from a number of objections, including some that are levelled at dualism.
In our description of how primary qualities and secondary qualities differ, we have swept aside one of the most important issues that arise, that of the ontological status of secondary qualities. Perhaps the simplest and least generous reading of Locke presents him as espousing the representative theory of perception with secondary qualities being imposed by the �eye of the beholder�.
�not �, but ��
The representative theory of perception harks back to the Platonic �veil of appearances� � the phenomenological world we inhabit consists of mental representations produced by our senses which bear some distorted relation to objects existing in an underlying reality. We each build up a subjective, private picture of this objective world, with everyone probably experiencing things slightly differently, their own version of postbox red, pain or the taste of chicken (cf Smart and colour??? xxx on bitterness). On this reading, the primary qualities are seen as fundamental, i.e. irreducible and ineliminable, properties of matter, and that this corpuscular (or �atomic�) matter interacts physically and causally at a low level with our bodies� perceptual mechanisms which interpret this activity in terms of sense data. Secondary qualities are thus deprived of their independent ontological status and Locke has to defend a full version of the representative theory of perception.
Instead, we can probably read Locke more sympathetically � add powers/grounds/bases �
Explain avoid use of the overloaded, misleadingly connotive term, �idea�. Locke appears very keen to defend secondary qualities as ontologically on a par with primary qualities, i.e. as inhering in the corporeal world, as opposed to being added post hoc by our perceptual mechanisms. The effect of a candle�s heat on wax, for examples, shows that the secondary qualities of one object affect another.
However, amongst the vital questions Locke�s distinction between primary� and secondary qualities raises� relates more to philosophy of mind than metaphysics � how is the corporeal world translated into experiential content. It would be unhelpful to demand that Locke furnish us with a perspective on the hard problem of consciousness, yet his theory of knowledge intimately binds his metaphysics/epistemology, empiricism and theory of mind.
matter behaves in complex ways no a macroscopic level