PROP. V.————
Distinction between the primary and the secondary qualities of matter.3. The qualities here referred to are those which our psychologists call the primary qualities of matter. It is here, then, that the distinction between the primary and secondary qualities comes under review. This distinction has played a conspicuous, though neither a very edifying nor a very successful part in philosophy. It is of some importance, however, in a historical point of view, as forming a chapter in the controversy between idealism and materialism; and therefore a short account of it shall now be given—if for no other purpose than that of showing how completely it has failed to answer its purpose, and how much it tends to keep up mistaken and contradictory notions in regard to the laws of knowledge.
Character of the secondary qualities.4. It is not necessary to present a complete enumeration of the primary and secondary qualities, or to go into any detailed explanation of their nature. A general view of the respective characters of the two classes will be sufficient to enable the reader to understand the distinction, and the use to which it has been turned by psychology. Among the secondary qualities are classed heat and cold, colour and sound, taste and odour. It will be observed that these words are of ambiguous or twofold import. They signify both certain sensations in us, and certain inferred qualities in things by which these sensations are induced. Thus the words
