they are not attributes of the things themselves; they are the results of the influences of primary qualities on us. Such secondary ideas are light, sound, smell, taste, &c.— We have previously met with this distinction in Galileo, Descartes and Hobbes. Locke adopted it from Boyle, the noted chemist, who is the author of the terms "primary and secondary qualities."
Whilst we are largely passive in acquiring simple ideas, we are active in forming from them, first, complex ideas, second, ideas of relations, third and finally, abstract ideas. Hence there are three forms of activity: composition, association and abstraction. We combine simple ideas into a single idea whenever we form ideas of attributes (modes), such as space and time, energy and motion. The ideas of such attributes as sensation, memory and attention are formed in inner experience. We form our ideas of things or substances by combining ideas of modes. But here a mystery confronts us. We know the single modes by themselves, but we are unable to tell what substance, which presumably supports the modes, really is. We may likewise place two ideas in juxtaposition, without forming a compound idea. We do this in all cases of ideas of relation, such as cause and effect, time and space relations, identity and difference.— Finally we are active also when we abstract or isolate an idea from its original connection. This happens when we form an idea of a color in general, or the idea of space without reference to its content.
b. Touching the matter of validity, Locke holds that there can be no question in the case of simple ideas because they are the direct effect of external objects. Even secondary qualities, which do not represent objects, are nevertheless the direct results of objective impressions.
