Colour and qualia

4. Functionalism

Functionalism is the view that mental states are definable in terms of their causal roles, their causal relations with stimuli, behaviour and other mental states (see Functionalism). Thus, arguably, something is a belief if and only if it is the result of perception or reasoning and the cause, with desires, of action. So a state would be an experience of subjective red just in case it was normally caused by viewing red things, it tended to cause judgments to the effect that something was red, and it generally related to other mental states – in particular through similarity judgments – in the way that is typical of experiences of red. Let us call the functional role in question ‘functional red’.

A more specific form of the functional/relational approach is to treat qualitative states as essentially representational, and qualitative content as representational content. The idea is this. When I have a reddish experience I am in the state of representing the object I perceive as having a certain property, in this case the property of being red. Immediately, of course, the question arises how to distinguish colour experience from mere colour belief. The standard reply is to appeal to the special functional role of the visual system, for example, by attributing to it some distinctive representational system all its own. The point is that to have a reddish experience is to represent an external object as red in this special visual way. This is a relational theory since subjective red’s identity is determined by its representational content, which is a matter of its relation to external objects, and it is a functional theory, since the particular functional organization of the visual system provides the basis for distinguishing experience from mere judgment.

One thorny problem for the representational approach involves the alleged representational content of the sensation. Above we said that subjective red is a representation that some object is red. But what is ‘being red’? As our earlier discussion showed, it is not easy to specify what property objective redness is, so it is correspondingly difficult to specify what the representational content of subjective red is supposed to be. There are various ways a representationalist can respond. If one believes that colour is identifiable with a spectral reflectance function, then that could be the content of the sensory representation. If, however, one denies the existence of objective colour, one could say that our sensory systems represent objects as having a property that they in fact do not have. This is the so-called ‘error theory’. Finally, one might be subjectivist about the content of subjective red itself. That is, one could say that a reddish experience is a report from the visual system concerning its own state – a way of saying, ‘I’m experiencing redly now’ (see Mental states, adverbial theory of).

Note that it is no objection to the first proposal that the alleged content has a complex theoretical structure and therefore could not plausibly be attributed to our sensory system. There are many representations we employ which in their internal structure are relatively simple and yet they refer to properties or objects which have a complex structure, and about which experts possess sophisticated theories. Take the well-worn example of water. According to most philosophers of language and mind, when I think about water I am thinking about a substance with the structure H₂O. But of course I do not have to know this, and it certainly is not plausible to claim that my mental representation of water contains representations of hydrogen and oxygen. Similarly, subjective red could function to detect, or register, a certain complicated property of an object’s surface without itself possessing complex structure.