Other common questions are what does it take for a person to persist as such from one time to another? Or what determine the past or future being that is you? Supposed that you find an old picture from your childhood and you recognize that child to be you, how do you know with certainty that it is really you? How do we define personal identity over time? One answer to this dilemma is the existence of the persistence in the conditions that remain the same in a person after undergoing change over time. Many philosophers define “person" as something that has certain special mental properties as intelligent, reasoning being. John Locke, for example, holds that personal identity is a matter of psychological continuity. According to this view, in order for a person X to survive a particular adventure, it is necessary and sufficient that there exists, at a time after the adventure, a person Y who psychologically evolved out of X. This idea is typically cashed out in terms of overlapping chains of direct psychological connections, as those causal and cognitive connections between beliefs, desires, intentions, experiential memories, character traits, and so forth. This Lockean view is well suited for thought experiments conducted from first-person points of view, such as body swaps or tele-transportation, but it, too, faces obstacles. For example, on this view, it appears to be possible for two future persons to be psychologically continuous with a presently existing person. Can one really become two? In response to this problem, some commentators have suggested that, although our beliefs, memories, and intentions are of utmost importance to us, they are not necessary for our identity, our persistence through time. At the same time, according to Locke the criteria for identity is memory, if we remember to have done or experience something then we are the ones who have done such action and that is what makes us unique to be considered a person.
However, memory cannot be counted as the only defining property of identity. For instance, if a person falls into a deep comma or a vegetative state, the human being under the comma would not be considered a person, since he or she have memory of the time spent under the comma. Therefore, based on Locke's argument this human being will cease to exist or awake as a totally different person since the person who he or she was before the vegetative state is not the one who woke up since the continuity of memory has been interrupted. At the same time Thomas Reid criticizes Locke's theory of personal identity for assuming a metaphysical hypothesis from the conceptual connection between memory and personal identity. On this theory, personal identity is based in memory. According to Reid, memory is neither necessary nor sufficient for personal identity, metaphysically speaking. Indeed, Reid holds that it is impossible to account for personal identity in any terms other than itself. Personal identity is simple. Though memory is not the metaphysical ground of personal identity, according to Reid, it provides first-personal evidence of personal identity. I know I was at the movies yesterday because I remember being there. Memories do not make one the same person over time. Rather, memories allow one to know one's own past, immediately and directly, in other words memories provide knowledge of actions and events but not necessarily of personal identity.
A second approach, the Somatic approach is that our personal identity through time consists in some physical relation. Personal identity is a matter of the same body over time. Whether we survive or perish has nothing to do with our psychological state or facts. Nonetheless, I think that the true lies somewhere between the two approaches. As a result, we need both mental and physical continuity in order to survive or perhaps either would exist or survive without the other. For example, supposed that your cerebrum, the part of the brain that is mostly responsible for the mental functions, is transported to another human body. Based on the Psychological Approach the other human being, who now has your mental features, would consider to also being you because of the psychological continuity. In this case identity is a one-one relation, meaning only identical to one thing and one thing only although not the same can be said in branching cases. Surprisingly, non-branching will mean then that if your brain is divided, you have a chance of surviving if only one half is preserved but you will die if both halves are destroyed.
Personally, I considered that the argument of what is personal identity is very similar to the argument of Nature vs. Nurture in Psychology. One can go either way depending on believes considerations or understanding on the topic, however, there is always the possibility that in reality it is a combination of both approaches. The same can be assumed for personal identity, though personally I see several advantages in supporting continuity as the criteria for personal identity. First, it fully captures the conception we have of ourselves as self-making agents. Second, while not reducing us to mere bodies, it yet avoids forcing us to take sides between the physical and psychological continuity approaches. Third, it incorporates psychological continuity into a more holistic and intelligible picture of personhood.
