(2) Moreover, the theory fails to explain the nature of that “possession” of the secondary qualities which it ascribes to the group of primary qualities. In what way, we ask, do the primary qualities have or possess the secondary? The only serious attempt to answer this question seems to be that of the numerous philosophers (Descartes, Galileo, Locke, etc.) who treat the secondary qualities as “subjective” effects of the primary qualities upon our sense-organs. Now, this familiar solution of the problem seems deficient in logic. For the one solid argument which has been advanced in favour of the subjectivity of secondary qualities seems to be the contention that they cannot be perceived without sense-organs of a special type. Colours, it is said, exist only for an eye, sounds for an ear, taste for a tongue, and so forth. And differences of structure or temporary condition in the sense-organ lead to the perception of different secondary qualities, as when, to take the stock examples, everything looks yellow to the jaundiced eye, the same water feels warm to one hand and cold to the other, and so forth. But these considerations seem just as applicable to the supposed “primary” as to the “secondary” qualities of things. Geometrical form, for instance, is imperceptible apart from sight or touch; motion, again, and consequently change of configuration, and similarly mass, which is a ratio of accelerations, require either sight or touch for their perception. Of course, we can think of motions and masses which we are not actually perceiving, just as we can think of an absent colour or smell, and in both cases we can in reasoning about motions or masses or colours or smells abstract altogether from the presence of a percipient. But this does not affect the fact that the mathematical qualities of body are just as dependent for perception upon the presence of a percipient with suitable sense-organs as anything else. Configurations, extensions, and motions which no one perceives by sight or touch or any other sense are exactly in the same case as a colour which no one sees or a sound which no one hears. The argument from the indispensability of a perceiving organ ought logically to tell just as much in the one case as the other.[78]