 Psychologists who have debated the rather astonishing claim that people who provide help to others often lose track of the distinction between themselves and the person being helped have proposed several different ways of determining whether this sort of “self-other merging” has occurred. Before considering these, however, we should remind ourselves of an important philosophical distinction that will be crucial in assessing tests for self-other  merging.[19]  The distinction is often made using the labels “qualitative identity” and “numerical identity”. Qualitative identity is the relation that often obtains between two TV sets manufactured by the same company. They share most of their important properties. Numerical identity is a relationship that obtains between a person at one time in his life and that same person at another time in his life. If the time gap is substantial, the person at the earlier time may differ in many ways from the person at the later time. When you were a baby, you weighed less than 10 kg, spoke no language, and couldn’t walk. But you now are numerically the same person as the baby. Numerical identity can be of enormous legal and moral importance, a point nicely illustrated by the trial of John Demjanuk, the Ukrainian-born auto worker who was accused of being the sadistic Nazi concentration camp guard whose victims called him “Ivan the Terrible”. The man on trial, in 1988, differed in many ways from the concentration camp guard: he was much older, heavier, bald, and spoke English. He was obviously not even close to being qualitatively identical with perpetrator of Ivan’s crimes. What the court had to determine was not whether Ivan and Demjanuk were qualitatively identical but whether they were numerically  identical.[20]  What makes this distinction important for present purposes is that the sort of identity that is relevant to the debate between egoists and altruists is numerical identity, not qualitative identity. If Sophia, at age 30, sets aside a large sum of money that will be paid to Sophia at age 70, young Sophia is not being altruistic. If her ultimate goal is to ensure that old Sophia has the means to live a comfortable life, then young Sophia’s action is straightforwardly egoistic. The take-home message here is that if a test used to determine whether person A takes herself to be identical to person B is to be relevant to the egoism versus altruism debate, the test must provide evidence that person A takes herself to be numerically identical to person B, not that she takes herself to be qualitatively identical to person B.