I am convinced that this popular and superficially plausible view is radically false, and that its logical consequence, the belief that the real existence of our fellows is less certain than our own, is a grave philosophical error. That the argument from analogy is no sufficient basis for the belief in human experience beyond my own, can easily be seen from the following considerations:—(1) As ordinarily stated, the data of the supposed inference do not actually exist. For what I perceive is not, as the subjectivist assumes, three terms—my own mental life, my own anatomical structure, and the anatomy of my neighbour, but two, my own mental life and my neighbour’s anatomy. If I cannot be sure of the reality of my neighbour’s experience until I have compared the anatomy and physiology of his organism with that of my own, I shall have to remain in doubt at least until science can devise a mechanism by which I can see my own nervous system. At present one of the terms on which the analogical argument is said to be based, namely, my own internal physical structure, has to be mostly taken on trust. It would be little less than the truth to invert the subjectivist’s position, and say that, until science can devise means for seeing our own brains, we infer the resemblance of our own anatomy to our neighbour’s from the previously known resemblance of his inner experience and ours. (2) And even supposing this difficulty already surmounted, as it conceivably will be in the future, there is a still more serious flaw in the presumed analogical inference. If I once have good ground for the conviction that similarity of inner experience is attended by similarity of physical structure, then of course I can in any special case treat the degree of structural resemblance between one organism and another as a sufficient reason for inferring a like degree of resemblance between the corresponding inner experiences. But upon what grounds is the general principle itself based? Obviously, if my own inner experience is the only one known to me originally, I have absolutely no means of judging whether the external resemblances between my own organism and yours afford reason for crediting you with an inner experience like my own or not. If the inference by analogy is to have any force whatever in a particular case, I must already know independently that likeness of outward form and likeness of inner experience at least in some cases go together. The plausibility of the usual subjectivist account of the way in which we come to ascribe real existence to our fellows, is simply due to its tacitly ignoring this vital point.