Personal Identity - Theories - Continuity of Substance - Bodily Substance

Bodily Substance

One basic concept of personal persistence over time is simply to have continuous bodily existence. However, as the Ship of Theseus problem illustrates, even for inanimate objects there are difficulties in determining whether one physical body at one time is the same thing as a physical body at another time. With humans, over time our bodies age and grow, losing and gaining matter, and over sufficient years will not consist of most of the matter they once consisted of. It is thus problematic to ground persistence of personal identity over time in the continuous existence of our bodies.

Nevertheless, this approach has its supporters. Eric Olson gives a definition of a human as a biological organism and asserts that a psychological relation is not necessary for personal continuity. Olson's personal identity lies in life-sustaining processes instead of bodily continuity. This biological approach squares with many other psychological accounts of personal identity but does not fall into common metaphysical traps.

Derek Parfit presents a thought experiment designed to bring out our intuitions about the corporeal continuity. This thought experiment discusses cases in which a person is teletransported from Earth to Mars. In the one case, the person enters the teletransporter and has each molecule of his body disassembled, teletransported to Mars, and then reassembled. In another case the person enters the teletransporter where that person’s body is destroyed while all the exact states of that person’s cells are recorded. This information is then teletransported to Mars, where another machine uses organic material to produce a perfect copy of that person’s body. The question is whether in either of these cases the person on Mars is identical to the person on Earth. Suppose that these two cases are just the furthest opposite points on a spectrum. In-between these two cases there are more cases in which an increase amount of the person on Mars is constituted of the numerically identical matter as the person on Earth. The question for that the criterion for personal identity becomes where on this spectrum does the person on Mars stop being identical to the person on Earth. Is it at 1, 51, or 99.9 percent? It appears that we are not able to draw a line. This inability appears to show that having a numerically identical physical body is not the criterion for personal identity.