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Locke 1

Locke on the distinction between primary and secondary qualities

We have already had some occasion to concern ourselves with this distinction which Locke makes in Chapter VIII between primary and secondary qualities. Descartes makes a similar distinction in the wax example in the Meditation II section 11. The distinction itself goes back to the Greek atomists. In spite of its antiquity, however, the distinction is so important to modern philosophy (Descartes to Hume) that David Hume says it characterizes modern philosophy.

The distinction between primary and secondary qualities captures the difference between the ways things are independently of how we perceive them, and those qualities of things which depend on how we perceive them. Thus, a tower or mountain presumably occupies space and remains (relatively) at rest, whether we perceive it or not. But the fact that the mountain appears purple from a distance is an artifact of the interaction of the object with a particular kind of perceptual apparatus. Dogs, for example, have no color receptors in their eyes, thus they see the world in shades of black and white. Human beings, who do have color receptors, see the world as a multiplicity of colors. Without a human perceptual apparatus, there would be light rays, and absorption of light rays, but no perceived color.

What are the primary qualities, and what are the secondary ones? Extension, figure, number and motion of bodies large enough to be observed is the list which Locke gives first. (II. 8, 12) These qualities produce in us the ideas of primary qualities. The secondary qualities are colors, such as white, violet and green; tastes, smells, and sounds. The primary qualities produce the ideas of secondary qualities by interacting with our perceptual apparatus. Thus without eyes and brains/minds, while there would be objects which absorb various light rays and light, there would be no perceived color. Without noses, nerves, brains and minds there would be no perceived smells and so on.

Locke goes on to observe (II, 8, 15) that the ideas of primary qualities resemble the properties in the objects which they represent, while this is not true of secondary qualities. Thus he says: "...that the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves, but the ideas produced in us by these secondary qualities have no resemblance of them at all."

The distinction connects skepticism, science and philosophy in interesting ways. One of the strands of skeptical thinking holds that the variability of our perceptions shows that they are mind dependent, and because reality is determinate, this variability shows that we are grasping appearance and not reality. Thus if you see an oar as bent and I see it as straight, we know that it cannot be both, it must be one or the other. But since we see it both ways, we have appearance and not reality. In fact, one of Locke's most famous examples (used by Berkeley as well) -- that of dipping a hand which is warm and the other hand which is cold into a bucket of water -- we find in Montaigne. But the scientist differs from the skeptic in holding that we can distinguish appearance from reality, we can tell which properties of things they have independently of us, and which depend on our perception. So, the skeptic sees all properties as appearance, while the scientists see only some properties as apparent, and others as representing reality. Thus, the distinction between primary and secondary qualities implies that we can know objective reality in a way which the skeptic denies is possible.


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