At the close of our last paper on personal identity we had just turned to the consideration of those apparent morbid divisions of the unity of consciousness which are sometimes, though happily rarely, brought under the notice of medical psychologists. Double consciousness, as we have already hinted, is essentially a result of diseased action, and comprehends a variety of conditions, distinguished from each other by differences in the mental symptoms, and by the relations to each other of the lucid and insane or of the two insane “oscillations.” In all of them, however, there is, for the time, a change, a perversion, or an exaltation, of the mental identity of the individual, of that principle which is, as it were, a centre round which the other faculties of mind revolve, and about which memories cluster. In the intensest forms of double consciousness, so called, mental identity is separated or multiplied into two distinct parts, so that two identities reside in the same individual, while in the milder manifestations of this condition there is a partial division of the same principle, a confusion of two natures in the same person. Where two alternating, though altogether unconnected, lives are lived by the same being, there is afforded, we think, a proof that mental identity is something more than consciousness, and so far independent in its affections. Indeed, it appears to us that the morbid states at present under examination would have been more aptly described as instances of double identity rather than of double consciousness. The phrase double consciousness is a contradiction in terms, for it is manifestly absurd to suppose that the mind can exist in two different states at the same moment. It is also a misleading expression, for this is not, of course, the meaning which it is intended to convey, nor is it at all descriptive of the conditions to which it is applied. These conditions are not necessarily characterised by any alteration of consciousness; that is to say, if consciousness is regarded as having reference simply to the present existing operation of the mind, for the man who inhabits alternately two distinct mental spheres may be perfectly conscious in both of them. In both of them his eyes, his ears, and all his organs of sense, may be normally active. In both of them, with equal accuracy, he may appreciate his surroundings, govern his movements, and express his ideas. In both of them he may be equally conscious, but he is not similarly conscious. The same world is inspected from different points of view in each. In the one it may be the real world, as it is to the perceptions of ordinary people; in the other, the world clad in the unsubstantial figments of a feverish fancy; or in both, a shadowy world, made up of metamorphosed realities. But whatever the metamorphoses may be, they arise, not from errors of perception, but of the personality—perceiving. A man who has passed into the abnormal phase of double consciousness sees all the familiar faces that surround him, but he does not recognise them; he hears loved and well-known voices, but they fall upon his ears as strange sounds; he beholds his household gods, but these do not, as they were wont, awaken emotion in his mind; in short, he regards everything in a new light and apart from former associations. The mind, shorn of its past, begins to learn the lessons of life anew, and perceives every object in relation to its new condition, the result of internal changes. The outward creation becomes subordinate to the inward idea, and is regarded only as it harmonises with the reigning delusion.