Unable as he was to explain how the same consciousness could persist throughout a succession of really and adequately distinct substances (except by virtually substantializing consciousness), Locke nevertheless persisted in holding that consciousness and consciousness alone (including memory, which, however, is inexplicable on any other theory than that of a subsisting and persisting substance or nature which remembers), constitutes personality and personal identity. We have dwelt upon his teaching mainly because all modern phenomenists try to explain personality on the same principles—_i.e._ independently of the doctrine of substance. As a corollary from his doctrine he inferred that if a man completely and irrevocably loses consciousness [or rather memory] of his past life, though he remains the same “man” he is no longer the same “person”: “if it be possible for the same man to have distinct incommunicable consciousness at different times, it is past doubt the same man would at different times make different persons”;(319) and he goes on in this sense to give a literal interpretation to the modes of speech we have referred to above.(320) He likewise admitted that two or more “persons,” _i.e._ consciousnesses, can be linked with the same individual human being, or the same individual human soul, alternately appearing and disappearing, giving place successively to one another. When any one of these “personalities” or consciousnesses ceases to be actual, it must in Locke’s view cease to be in any sense real: so that there could not be two or more personalities at the same time in the same individual human being. Modern psychologists, however, of the phenomenist school, convinced that sub-conscious mental activities are not only possible, but that the fact of such activities is well established by a variety of experiences, have extended Locke’s conception of personality (as actual consciousness) to embrace groups of mental activities which may emerge only intermittently “above the threshold of consciousness”. Hence they explain the abnormal cases of double or multiple consciousness already referred to, as being manifestations of really distinct “personalities” in one and the same human individual. In normal human beings there is, they say, only one normally “conscious personality”. The sub-conscious mental activities of such an individual they bulk together as forming this individual’s “sub-liminal” or “sub-conscious” _Ego_ or “self”: presumably a distinct personality from the conscious one. In the abnormal cases of “double-consciousness” the subliminal self struggles for mastery over the conscious self and is for a time successful: the two personalities thus for a time changing places as it were. In the rarer or more abnormal cases of treble or multiple consciousness, there are presumably three or