ABSTRACT
In Chapter 3 I outlined some of the enormous consequences that ¯owed from the distinction made by Galileo and John Locke in the seventeenth century between the primary and secondary qualities of matter. The primary qualities were those that appeared to exist independently of the observer and that could be measured; typically, they were expressed in numbers, and they included such things as mass, dimension and velocity. The secondary qualities were those whose character depended on the nature of the human senses; they included such things as colour, taste, heat, beauty and so on. These are qualities which exist in the observer's subjective experience, and we can never be quite certain that one observer's experience of them is the same as another's. Locke (1689) described the primary qualities as `real', with the implication that the secondary qualities were in some way unreal, or less real.
