PROP. V.————
find it difficult to show that the words which express the primary qualities are one whit less ambiguous than those which denote the secondary. Are not the words "extension," "figure," and "solidity," employed both to express these qualities as they are in themselves, and also to express our perceptions of them? Is not this precisely the same ambiguity which the terms significant of the secondary qualities present? Is psychology able to explain, or is any human being competent to know what these qualities are, apart from his perceptions of them? It is always our perceptions of the primary qualities, and not these qualities themselves, which come before the mind, just as it is always our sensations resulting from the secondary qualities, and not the secondary qualities themselves, that we are cognisant of. The terms, therefore, which express the primary qualities, are just as ambiguous as those which indicate the secondary; and the attempt to remove this ambiguity, by means of the distinction in question, instead of removing, serves only to disguise it The attempt to establish a clear doctrine of perceptive knowledge, by distinguishing the two classes of qualities, establishes only an obscure and misleading one.
7. But the error lies not so much in this distinction itself as in its application. In the hands
