If a person has a multiple personality disorder, are they one individual, or
What used to be called multiple personality disorder (MPD) is now called dissociative identity disorder (DID) in DSM, the Diagnostic and Statistical Manual of Mental Disorders, and the change in terminology may reflect a possible change in thinking. A personality (e.g. a television personality) is in one sense a person, but generally I and my personality are not the same (Same what? Same entity, presumably, if that is any help!) In any case, since my personality might change considerably over time, while I remain the same person or the same individual (I assume that individual and person, as they are applied to human beings, are equivalent concepts), the two cannot be identical. And most of us do exhibit slightly different personalities, for example at home and at work, or with friends and with superiors. Those who have a mixed ethnic or national heritage can sometimes find that they have two personalities, say one English and one Indian. They may feel the pressure on the integrity of the person. But since personality and person really are distinct concepts, they should not feel this pressure. After all, if Mr. X, who is half in Indian culture and half in English culture - as though there were only one of each! - commits some awful crime, then it is Mr. X who will be punished, no matter which personality he is manifesting or which country he is charged in. The two concepts, of personality and of person, could without too much of a stretch be called the psychological and logical (or metaphysical) concepts, respectively. Now the question is whether a change in the application of the psychological concept forces a change in the application of the logical or metaphysical concept. The answer to this seems to be negative, as I have said. Certainly if we say that in DID we are confronted with two or more individuals or persons, individuals falling under the category of person, we are implicated in a psychological concept of personal identity rather than a physical one. The criterion of identity is not the body, but the consciousness. This was Locke's view, and in the Essay concerning Human Understanding he proposes a celebrated thought-experiment in which the consciousness of a prince, and with it the soul of the prince, is transported into the body of a cobbler. The question he asks is whether the person before us is the cobbler or the prince, and his answer, relying on the consciousness criterion, is that it is the prince, although he also says that the man or human being is the cobbler. Now all we have to do is to imagine the prince vacating the cobbler's body, and the cobbler's consciousness taking up residence there again, and we have a description of DID as it might be seen by the proponent of the consciousness criterion. Overall, given that the concept of a person is partially a forensic or legal one ('It is a Forensick Term . . .'), as Locke observes, as well as a metaphysical and logical one, and given the improbability of Locke's scenario, it seems better to say that in DID what we observe is an oscillation between personalities, not individuals, though one marked by the extremeness of the difference between the personalities and the lack of communication between "them", manifesting as memory loss. This is supported, I think, by a consideration of the proposed origins of DID in childhood trauma.