only in the percipient. Without the eye, there would be no colours; without the ear, no sounds, and
so on. For Locke's view as to secondary qualities there are good grounds--jaundice, blue
spectacles, etc. But Berkeley pointed out that the same arguments apply to primary qualities. Ever
since Berkeley, Locke's dualism on this point has been philosophically out of date. Nevertheless, it
dominated practical physics until the rise of quantum theory in our own day. Not only was it
assumed, explicitly or tacitly, by physicists, but it proved fruitful as a source of many very
important discoveries. The theory that the physical world consists only of matter in motion was
the basis of the accepted theories of sound, heat, light, and electricity. Pragmatically, the theory
was useful, however mistaken it may have been theoretically. This is typical of Locke's doctrines.
Locke's philosophy, as it appears in the Essay, has throughout certain merits and certain demerits.
Both alike were useful: the demerits are such only from a theoretical standpoint. He is always
sensible, and always willing to sacrifice logic rather than become paradoxical. He enunciates
general principles which, as the reader can hardly fail to perceive, are capable of leading to strange
consequences; but whenever the strange consequences seem about to appear, Locke blandly
refrains from drawing them. To a logician this is irritating; to a practical man, it is a proof of
sound judgement. Since the world is what it is, it is clear that valid reasoning from sound
principles cannot lead to error; but a principle may be so nearly true as to deserve theoretical
respect, and yet may lead to practical consequences which we feel to be absurd. There is therefore
a justification for common sense in philosophy, but only as showing that our theoretical principles
cannot be quite correct so long as their consequences are condemned by an appeal to common
sense which we feel to be irresistible. The theorist may retort that common sense is no more
infallible than logic. But this retort, though made by Berkeley and Hume, would have been wholly
foreign to Locke's intellectual temper.
A characteristic of Locke, which descended from him to the whole Liberal movement, is lack of
dogmatism. Some few certainties he takes over from his predecessors: our own existence, the
existence of God, and the truth of mathematics. But wherever his doctrines differ from those of
his forerunners, they are to the effect that truth is hard to ascertain, and that a rational man will
hold his opinions with