colour

Colour is the most prominent example of a secondary quality (see primary/secondary qualities ). Philosophical opinion has always been divided over whether to allocate colour (and smell, taste, and sound) to the physical world, or to regard them as holding their ‘residence entirely in the sensitive body; so that if the animal were removed, every such quality would be abolished and annihilated’ ( Galileo, Opere Complete, vol. iv). The atomists and Epicureans of the ancient world held the latter view, and it returned to popularity with the rise of 17th-century science. More accurately, we can distinguish at least five general families of philosophical position: (i) colours of things are the microphysical structures responsible for the different reflectances of light of different wavelengths by their surfaces; (ii) colours are the powers or dispositions bodies have, in virtue of these structures, to affect our visual experience in particular ways; (iii) colours are properly qualities of experience itself, displaced or projected onto external things; (iv) colours are complex dispositions of the perceiving subject, differentially triggered by different surfaces; (v) colours are to be identified with complex neurological events. The last two are a subjective mirror-image of the first two positions. Many of these suggestions face well-aired problems: whether they are even consistent with the fact that colours are visible, for example, and whether they make them intersubjectively accessible. Mixed and more complex theories are also found. Recent colour science has highlighted the extremely complex function of energies at different parts of the electromagnetic spectrum that result in things being perceived as one colour or another. Such work, emphasizing the active role of the brain in generating a definite experience from the complex flux, has tended to favour theories on the more subjective side of the fence, but the topic is currently wide open, even to the point of some theorists craving a pre-Galilean, Aristotelian, innocent confidence that the world is, in itself, coloured just as we take it to be. One interesting constraint on a successful theory of colour is its ability to explain various necessities: that yellow is a bright colour, that there cannot be transparent white, nor a grey flame.