Personal identity through time

Qualitative and numerical identity:Qualitative identity - e.g. 'I have the same television at home' (Same qualities)Numerical identity - e.g. 'I sat in the same seat as last week' (Exactly the same)Correspondingly there are two types of change: qualitative and numerical For example; if i was given a new bike and decided to change the paint and the tyres the bike would have undergone some qualitative changes however it retained its numerical identity. However if I melted the bike down so that it was no longer a bike it would have undergone such a radical qualitative change that its numerical identity was also changed. For people who have undergone severe brain damage it can be argued that they remain the same person but the person they were no longer exists. They retain their numerical identity whilst undergoing a qualitative change. A river is constantly changing, yet it still remains the same numerical identity. 

Unity of identity: The ability to consider oneself to be the same person in different times and places is an important characteristic of personhood. Descartes argued that the essential self was a 'rational soul' - a being that thinks, which is somehow united to the body but which can survive death. Therefore the essence of self must be non-physical.Our bodies are composite and therefore can be destroyed however the mind is not, therefore it must be immortal. Descartes' concludes that personal identity is mental, to do with thoughts, beliefs, memories and character. Therefore I can undergo any number of physical changes and still maintain my personal identity - the 'I' or 'self' cannot die. However this invites the prospect of personal identity maintaining through reincarnation. If the essential self is the soul, and the soul survives bodily death, we must be able to consider ourselves the same person after reincarnation. Locke argued that if you cannot conceive of yourself as the same person after reincarnation this would suggest that the containing existence of a rational soul through time is not sufficient for personal identity through time. Hume disagreed with Descartes and argued that we 'discover' our identity through memory as 'memory alone acquaints us with the continuance and extent of this succession of perceptions'. However is it physical or psychological continuity that endures through time? 

Physical continuity through time:We are not physically continuous through time: we lose hair, brain cells and skin, some people may have organ transplants or plastic surgery. However despite all the changes, our bodies exist continuously. For example, in the Greek legend of Theseus' ship different parts of the ship were changed and replaced over many years. Eventually all the parts were replaced. Was it the same ship? Locke suggested that as long as the organisation between the parts remains the same it will be the same entity. If it retains its 'vital union' and there are no radical breaks, we think of it as the same organism. 

Is physical continuity through time a necessary condition of personal identity?Parfit imagines that we are going to be 'teleported' through a machine that scans our mental and physical structures, destroys us then replicates us somewhere else. When we arrive in the new place we look the same, have the same memories, interests and experiences. Our personal identity is in tact even though we do not have a body. Therefore it is not a necessary condition for continued personal identity. 

Is physical continuity through time a sufficient condition of personal identity? Shoemaker proposed that two men suffering from brain tumours were operated on. The operations consisted of brain extractions but the assistant accidentally put Mr Brown's brain back into Mr Robinson's body and vice versa. One of the patients died but the one with Mr. Robinson's body and Mr. Brown's brain survived. When asked his name the patient said 'Brown' and he recognised Brown's family as his own. If we can accept that Robinson has not survived, as Brown has, even though his body continues to exist, we have to conclude that physical continuity through time is not sufficient to ensure personal identity through time. 

Although we have seen that we could have large parts of our bodies removed and still maintain personal identity, many people would argue that if the brain were replaced continued personal identity would cease. We can therefore argue that the brain is the part of the body that contains the necessary features of personhood and that although physical continuity of the body is not necessary for personal identity but continuity of the brain is. 

Psychological continuity through time: Locke argued that our personal identity is based on the unity, continuity and connectedness of our conscious experiences. Memory is central to personal identity - if I remember doing something, then I am the same person that did that thing. It is the extension of consciousness to the past, and it is through our consciousness that we remain the same person through time. For example, if the soul of a prince, with all its memories and experiences, entered the body of a cobbler it would be the same person as the prince but not necessarily the same man. The consciousness would belong to the prince but the physical substance would belong to the cobbler. A consequence of this theory is that two persons could occupy the same body, as in Dr Jekyll and Mr Hyde or cases of multiple personality disorder. 

However, Butler argued against Locke, suggesting his argument is circular because the consciousness of personal identity presupposes personal identity. For example, if I am aware that I got up this morning and I can remember getting up yesterday morning then I can be confident that the experiences are mine and I am the same person. But this doesn't mean that memory makes these experiences mine. It's not because I remember getting up yesterday that it was me but that I remember it because it was me.

Is psychological continuity through time a necessary condition of personal identity? Reid disagreed with Locke and demonstrated that we do not remember everything we have done and what we can remember changes over time. For example a soldier may remember being a child  however when the soldier ages and becomes a general he can not remember being a child, however he can remember being a soldier. If we claim that he is the same person throughout his life, then we are suggesting that personal identity can survive through time without psychological continuity. Even though the general does not remember being the boy, there is a transitivity of identity. The general now remembers being the soldier, who at that time could remember being the boy. In this way the boy and the general are connected. 

Is psychological continuity through space and time a sufficient condition of personal identity?Derek Parfit imagined that he and his two brothers were in an accident. All their brains were damaged and in an attempt to save the two brothers, Derek's brain was split in two and each half was transplanted into his brothers. Each of the resulting people believe they are Derek Parfit, with his memories and seems to be psychologically continuous with Derek. If psychological continuity is sufficient for personal identity then both brothers will have the same numerical identity - they will be the same person. This can not be possible as one person can not become two persons and have the same numerical quality. Therefore psychological continuity does not seem to be sufficient for personal identity.This is further proved if we imagine that one brother kills the other. They clearly cannot be the same person if one is still living and the other is dead. 

Hume argued that in fact there is no personal identity over time - only a 'bundle or collection of different perceptions' linked together by causation and resemblance. Personal identity is a psychological illusion - we get the idea because one experience causes another and we begin to think of our life as an 'identity'. The problems of more than one man being the same person or one man being multiple persons are cause when we try to assign a personal identity though space and time. 

Parfit instead argues for a 'best candidate' theory of personal identity - that psychological continuity is what matters, rather than personal identity. As we grow older we are not the same person as were 20 years ago, although something of the child remains inside of us. For example if we consider the city of London. It is not the same as it was in 1300 or 1660 however it is still London because the character of London survives and there is continuity between all of these different Londons. 

However this view seems to go against how we feel about our own personal identity. When I look back at my actions I feel as if those actions were 'me' and that feelings and memories are part of a continuous me, not a series of connected 'me's'.  This is why we have a sense of moral responsibility for our past actions.

Qualitative and numerical identity + Descartes

Physical continuity through time

Psychological continuity through time

Do we have identity through time?