primary/secondary qualities

The division is especially associated with the 17th-century rise of modern science, with its recognition that the fundamental explanatory properties of things are not the qualities that perception most immediately concerns. These latter are the secondary qualities, or immediate sensory qualities, including colour, taste, smell, felt warmth or texture, and sound. The primary properties are less tied to the deliverance of one particular sense, and include the size, shape, and motion of objects. In Boyle and Locke the primary qualities are scientifically tractable, objective qualities essential to anything material: the minimal list is size, shape, and mobility, i.e. the state of being at rest or moving. Locke sometimes adds number, solidity, texture (where this is thought of as the structure of a substance, or way in which it is constituted out of atoms). The secondary qualities are the powers to excite particular sensory modifications in observers. Locke himself thought in terms of identifying these powers with the textures of objects that, according to corpuscularian science of the time, were the basis of an object's causal capacities. The ideas of secondary qualities are sharply different from these powers, and afford us no accurate impression of them. For Descartes, this is the basis for rejecting any attempt to think of knowledge of external objects as provided by the senses. But in Locke our ideas of primary qualities do afford us an accurate notion of what shape, size, and mobility are. In English-speaking philosophy the first major discontent with the division was voiced by Berkeley, who probably took the basis of his attack from Bayle, who in turn cites Foucher . Modern thought continues to wrestle with the difficulties of thinking of colour, taste, smell, warmth, and sound as real or objective properties of things independent of us.