Reductionism is a belief that all complex phenomena can be explained by simplifying the whole concept into basic constituent parts. In his book ‘Reasons and Persons’ Parfit outlines how a reductionist would explain personal identity. The idea is that by conceptually isolating certain features of a person, we can come to understand what the crucial feature is that bases the concept of a person. He claims a person’s existence to involve nothing outside of the physical and psychological experiences one has. He expands upon this in Chapter 10 of his book, ‘A persons existence just consists in the existence of brain and body, the doing of certain deeds, the thinking of certain thoughts, the occurrence of certain experiences, and so on.’ He claims all reductionist would accept this description.
He also highlighted a psychological criterion and a physical criterion to explain the components of ones identity in an attempt to simplify the ambiguous nature of what makes a person themselves. He outlined the psychological criterion as the non-branching mental continuity and/or connectedness between the facts and information one has experiences in their life. Parfit believed this to be where ones personality or identity stems from, so therefore personal identity can be reduced to this psychological continuity. Both the psychological and physical criterion rely on the idea of the continuity within a functioning brain, and this is where Parfit’s theory of persistence is supported. This means that one may persist over time as a result of being connected through a chain of links that are not affected by the passing of time or ones development. So resultantly, although a person 50 years in the past may appear physically or psychologically dissimilar to their current selves, the idea of continuity means they are still the same person. Furthermore, since personal identity exists only in psychological continuity, it takes a non-branching, or one-one form. Personal identity is, as Parfit puts it, ‘not what matters.’ What does matter is the psychological continuity and connectedness, and the intrinsic feature of a person that result.
Parfit acknowledges that his views on personal identity may be counterintuitive and contrary to what many people ordinarily believe the nature of a person is. Resultantly, Parfit states that ‘even if we are not aware of this, most of us are Non-Reductionists. It thus follows that most of us have false beliefs about our own nature, and our identity over time.’ As mentioned, a non-reductionist, for example, Cartesian view of personal identity outlines that a person is a mental substance rather than a brain and a body. What matters in the Cartesian perspective is the persistence of a nonphysical, mental ego that makes each person their own self. Parfit rejects the non-reductionist view, according to him, there is no Cartesian ego as shown by his ‘My Division’ thought experiment. This also acts as supporting evidence for his reductionist view.
As mentioned, some supporting evidence for Parfit’s can be found in his thought experiment ‘My Division’, which is present in Persons and Reasons. This theoretical explanation entails a fission of the two hemispheres of his brain which ‘have the same full range of abilities’ (p255), which are then transferred into another two ‘de-brained’ bodies. Allowing for the incredulousness of the example, we now have two fully functioning human organisms operating via the two halves of Parfit’s brain. Each of them should have the same psychological make up and continuity so therefore the same personal identity according to Parfit. Although the experiment has been criticised for its realism, Parfit defends it, it has been shown that our brains can indeed be split by dividing the corpus collosum, which is precisely what happens for split-brain patients undergoing surgery. Therefore, this may suggest a similar experiment could maybe be attempted in the near future to ratify his experiment. However, there are still many ethical concerns if this was to be put into practice so tangible support remains to be seen. ‘My Division’ is one of the cases that Parfit attempts to demonstrate that his ideas are accurate, however the support provided for his theories is not entirely valid.
The theoretical nature of the experiment means it is not very cogent and relies on empiricial assumptions that may suggest the conclusions found may have been affected by a biased interpretation. Parfit assumes that because split brain patients can function normally with only one half of their brain, one could split a brain in half and expect the same level of functioning. A functional plasticity of ones brain may allow it to take over various functions of an area of the brain that has been damaged, but until Parfit’s example has been falsified through legitimate experiment rather than conjecture it is difficult to accept this as support for his ideas. So resultantly, this reduces the credibility of Parfit’s case for reductionism.