Secondary qualities

Primary qualities are generally defined as those properties that objects have independently of being perceived. Standard examples would include properties of shape, weight, position, electric charge, atomic structure. These properties characterize the way the world is in itself, separately from mind. Secondary qualities, by contrast, are defined as those properties that incorporate sensory responses in their conditions of application, so that the idea of a perceiver is built into their nature. It is more controversial which properties, if any, belong to this category, since not all philosophers agree that the standard alleged examples of secondary qualities – colours, sounds, tastes, smells, feels – are really correctly so classified. Some thinkers hold that objects have only primary qualities. Let us note the significance of the question, concentrating on the case of colour, which is the one most frequently discussed.

Objects appear to have both shape and colour in equal measure, but is this really how things are? Depending upon how we answer this question, we get very different pictures of the relation between appearance and reality. If both sorts of property are equally out there, equally objective, then what appears to us in perception is reality itself. When we see a material object we see something that exists independently of our seeing it, and we see the object as it is whether or not there are (or even could be) any perceivers. But if the colour of the object is inherently dependent upon our sensory responses, then the question arises as to whether what we see is really in some way itself mental. If colour is a secondary quality, in other words, do we see things as they really are? What is it that bears colour if colours are in some way mentally constituted? Do we indeed see anything at all, as distinct from introspecting the features of our own subjective states?