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ISSN 2311-7133 (Online)
There are two possible contexts of discussions about personal identity: philosophical and psychological. When psychologists speak about personality, as in the cases of amnesia or dissociative identity disorder, they take personality to be a property of human beings. Personality can change, but people whose personality it is will stay the same until they die. What a philosopher thinks about the criteria of personal identity depends on what she thinks about the ontological status of consciousness. Personal identity debates in philosophy emerged immediately after Descartes raised the ontological status of consciousness, declaring that it is a substance on a par with matter and it must, presumably, have its own criteria of identity. These debates have been continuing ever since, with materialists, dualists, functionalists and eliminativists having their different opinions concerning personal identity. Derek Parfit claims that the issue should be abandoned, because the category 'person' doesn't refer to anything ontologically real. His claim depends crucially on his famous thought experiment concerning brain division and subsequent transplantation of two brain hemispheres in two different bodies. Parfit argues that this thought experiment shows that a person can survive even in the case when we can not say whether this person is identical with any past or future person. Identity is indefinite and not important, it is survival that matters. However, I present a different interpretation of this thought experiment and argue that the experiment can not be considered as a proof that criteria of diachronic identity of persons differ from the criteria of diachronic identity of other objects. It is important for Parfit that in his thought experiment two resulting people be psychologically indistinguishable. It is also important for him that the experiment should be based on empirically possible scenario. I argue that from what we know thanks to contemporary neuroscience it is empirically impossible that two resulting people be psychologically identical. I also argue that the experiment can not be saved by rendering it purely conceptual. If the experiment is only conceptually possible it doesn't show what it is intended to show. We can imagine that there was a situation when a human being had two identical brain hemispheres, each perfectly functional after the operation, so that two resulting people are psychologically indistinguishable. However, this situation can be reinterpreted: maybe this operation is a way to realize that there has never been one human being with identical hemispheres, but Siamese twins sharing all the parts of their body except brain hemispheres. In this case the operation will not show that personal identity is indistinguishable, it will just show that it is possible to separate Siamese twins by giving them different bodies. Since both hypotheses are conceptually coherent there is no way to prefer one of them. Therefore I claim that Parfit's conclusion concerning non applicability of personal identity to this situation doesn't follow.
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