Personal Identity and Psychological Reductionism
When we tackle the question of 'What makes us the individual persons that we are?', one approach that we can take is to seek an answer to the question of what it is that is required for a person to continue to exist over time. If we could agree on what is required for it to be true that you continued to exist, then we would have good grounds to believe that we had discovered what makes someone the particular person they are, and by extension, what makes any person the person they are. In essence, what we are searching for are the necessary and sufficient conditions for personal identity over time.
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Where Psychological Reductionists believe that Descartes went wrong was to suppose that personal identity was fixed by the substance that was doing the thinking, rather than the thoughts themselves. To illustrate this point we can look at John Locke's thought at experiment which, for many, dealt a fatal blow against the idea that the self is an immaterial substance. Locke's experiment is presented by Joseph Chandler as follows:
Let anyone reflect upon himself and conclude that he has in himself an immaterial spirit, which is that which thinks in him and in the constant change of his body keeps him the same. Let him also suppose it to be the same soul that was in Nestor or Theristes at the siege of Troy, but he now having no consciousness of any of the actions of either Nestor or Theristes, does he or can he conceive of himself to be the same person with either of them? Can he be concerned in either of their actions, attribute them to himself, or think of them his own, more than the actions of any other men that ever existed?
According to Chandler, in the above thought experiment we have to consider what would be the case if we had 'immaterial spirits', which were thought to be the basis of our personal identity. If this was so, then the kind of reincarnation described in the experiment would certainly be possible. So, according to Locke, if all this were true, it would nonetheless be absurd to say that you were the same person as Theristes. The reason being that because the whole idea of being the same person implies sameness of consciousness i.e. having the same thoughts, plans, feelings and memories. Now since this sameness of consciousness is not preserved in reincarnation, the continued existence of an immaterial spirit cannot be sufficient for the continued existence of a person.
John Locke is regarded by many as the originator of the psychological theory. He argued that a person at an earlier time is the same as a person at a later time if the later person remembers all the experiences of the earlier one. This is asking a lot. A more plausible definition would be based on chains of remembering — today you can remember most of yesterday's experiences and tomorrow you will remember most of today's, and the day after that most of tomorrow's, and so on. So in a year's time there will be a chain of remembering leading back to yesterday, and indeed leading back to your birth, which you will now have no memory at all. Locke clearly believed that memory was not the only factor and that a person at an earlier time is psychologically continuous with a person at a later time if from that later person there is a chain of linked memories and emotions and plans and character going back to the earlier time. So that what really matters to the psychological reductionist is that there is a continuity of mental life, so that although our beliefs, desires, plans and personalities do change, they do so gradually. Even though we do sometimes undergo...