Colour and qualia

2. Subjective, ‘qualitative’ colour

The puzzle concerning subjective colour is an instance – perhaps the most discussed instance – of the general puzzle concerning the qualitative, or phenomenal, character of conscious mental states: the puzzle of ‘qualia’. We will continue to restrict our attention to colour experience, but most of the positions and arguments we review can be applied to the more general issue of phenomenal experience as a whole. Moreover, when it comes to visual experience, colour provides the most compelling challenge to an account consistent with physicalism. Indeed, we now need to ask the same question about subjective that we asked about objective colour: what sort of physical property could it be?

One obvious way of sorting properties is to distinguish intrinsic from relational properties. To a first approximation, intrinsic properties are those that an object possesses in virtue of conditions wholly within the object. Relational properties are those that an object possesses in virtue of its standing in some relation to other objects. So, for instance, my body’s mass is an intrinsic property, whereas its weight is relational, since it depends on my body’s location relative to the gravitational field generated by another object. (I weigh less on the moon than on the earth, though my mass is the same.)

Let us call the reddish qualitative character of my visual experience of the shirt ‘subjective red’. Is subjective red an intrinsic property of my experience? At first blush, it certainly seems to be. But, given the constraints of physicalism, if subjective red is an intrinsic property of my experience, and if my experience enters causal transactions with other states (or events) in virtue of its qualitative character, then subjective red must be somehow reducible to, or composed of, a physical property of my nervous system.