Primary and secondary qualities

The "new way of ideas" is thus hard put to it in accounting for the universal element in knowledge; it has even greater difficulties to face in defending the reality of knowledge. And, in the latter case, the author does not see the difficulties so clearly. His view is that the simple idea is the test and standard of reality. Whatever the mind contributes to our ideas removes them further from the reality of things; in becoming general, knowledge loses touch with things. But not all simple ideas carry with them the same significance for reality. Colours, smells, tastes, sounds, and the like are simple ideas, yet nothing resembles them in the bodies themselves; but, owing to a certain bulk, figure, and motion of their insensible parts, bodies have "a power to produce those sensations in us." These, therefore, as called "secondary qualities of bodies." On the other hand, "solidity, extension, figure, motion or rest, and number" are also held by Locke to be simple ideas; and these are resemblances of qualities in body; "their patterns do really exist in the bodies themselves"; accordingly, they are "primary qualities of bodies." In this way, by implication if not expressly, Locke severs, instead of establishing, the connection between simple ideas and reality. The only ideas which can make good their claim to be regarded as simple ideas have nothing resembling them in things. Other ideas, no doubt, are said to resemble bodily qualities (an assertion for which no proof is given and none is possible); but these ideas have only a doubtful claim to rank as simple ideas. Locke's prevailing tendency is to identify reality with the simple idea, but he sometimes comes close to the opposite view that the reference to reality is the work of thought.