The scepticism of Aristippus and the Cyrenaics mediated between the views of Protagoras and those of Gorgias, while marking an advance on both. According to this school, we know nothing beyond our own feelings, and it must be left undecided whether they are caused by an external reality or not. Nor can the feelings of one individual justify us in reasoning to the existence of similar feelings in the mind of another individual.[221] It might be objected that the arguments advanced in support of the latter assertion are suicidal, for they are derived from the abnormal states of consciousness accompanying particular diseases, or else from the divergences of taste exhibited by different individuals even when in good health,—an apparent admission that we are sufficiently well acquainted with the phenomena in question to institute a comparison between them, which, by hypothesis, is impossible. And this is, in fact, the method by which Mr. Herbert Spencer has endeavoured to upset the whole theory of subjective idealism, as involving at every step an assumption of the very realities that it professes to deny. But the Cyrenaic and the modern idealist have a perfect right to show that the assumptions of their adversaries are self-contradictory; and the readiest way of so doing is to reason from them as if they were true. The real answer to that extreme form of idealism which denies the possibility of making known our feelings to each other is that, our bodies being similarly constructed and responding to similar impressions by similar manifestations, I have the same sort of warrant for assuming that your states of consciousness are like mine that I have for assuming you to exist at all. The inference must, of course, be surrounded by proper precautions, such as are seldom used by unscientific reasoners. We must make sure that the structure is the same and that the excitement is the same, or that their differences, if any, are insignificant, before we can attribute the same value to the same manifestations of feeling on the part of different persons; but that this can be done, at least in the case of the elementary sensations, is shown by the easy detection of such anomalies as colour-blindness where they exist.