On Personal Identity Over Time Chan, Lik Hang Nick Course title: Knowledge and Reality – an Introduction to Epistemology and Metaphysics, offered by the School of Philosophy Date: August 2005 Heraclitus claims that we could not step into the same river twice (Plato, 1997, p.120). I do not think he is right. In this short essay, I am going to evaluate this problem, with the reference to the issue of personal identity over time, first by putting forward my own opinion, then by analogy with the ideas of John Locke and David Hume. Discussion on the definition of person is beyond the scope of this essay. Thus, I will simply use John Locke's definition. That is, "a thinking intelligent being, the same thinking thing, in different times and places; which it does only by that consciousness which is inseparable from thinking," and "it being impossible for anyone to perceive, without perceiving that he does perceive," and "the sameness of a rational being" (1961, p.280). Heraclitus would be right if he said we could not step into the same "water" twice. Because of "water" flow in the river, one could hardly step into the same "water", same "element" or same "H2O" twice. However, we can step into the same river more than once. Despite the fact that the river consists of different "water" between now and few hours later, we certainly know that there is only one river. Likewise, I know me-ten-years-ago and me-today are the same person. Obviously and undoubtedly, there are some changes on my body. The numbers of atoms I consist today are probably not the same as that ten years ago. I have new experience, which I do not have ten years ago. But I am sure I am still myself. A river may simply consist of water and river plate. Several factors or components make up personal identity over time. These include DNA, sex, personality, memory, brain, ability or skill, consciousness, habit, outlook, etc. Notice that only DNA is unchangeable. For instance, I could not play any musical instrument ten years ago and I can play guitar now. This does not make me a different person. Several components together make up personal identity. One component, say, memory, cannot do so. John Locke suggests that I-today is the same person as I-yesterday only if I-today have a sense of myself that includes a memory of I-yesterday. He may accept that I-today and I-fifteen-years-ago fail the criterion and therefore I-the-overall-person did not exist fifteen years ago (Hetherington, 2003, p.9). This is too strict. Imagine the river again, it may contain the same "water" as a few minutes ago. But it is unlikely to consist of the same "water" a few days later. Personal identity and memory are much more complex than rivers. In the movie Eternal Sunshine of the Spotless Mind, there is a service that allows people to "delete" a person in his mind. To do this, a map is drawn by recalling the person to be deleted. It seemed to omit unconscious. It is quite impossible to recall one's memory of another person in a short time. Similarly, one could quite hard to recall his memory fifteen years ago. So, as Hetherington says, I-today and I-fifteen-years-ago would fail Locke's criterion (2003, p.9). David Hume would partly agree with this. As Hume states, "for how few of our past actions are there, of which we have any memory? Or will he affirm, because he has entirely forgot the incidents of these days, that the present self is not the same person with the self of that time; and by that means overturn all the most establish'd notions of personal identity?" (1964, p.542) He does not believe that memory is a major factor of personal identity. I think memory is sometimes a major factor of personal identity. Unlike a river, where the same "water" probably would not remain in it for a few years, a normal person usually has memory of a few years ago. Hume further says that personal identity depends on the relations of ideas (1964, p.543). This is true and, again, we cannot use the river to make a comparison. In brief, I do not think that what Heraclitus said is right. We could not step into the same river twice. Persons may be like rivers in some sense. But due to the complexity of human being, rivers are not completely comparable with human in further discussion.   Bibliography Hetherington, S. (2003) Reality? Knowledge? Philosophy! An Introduction to Metaphysics and Epistemology. Edinburgh: Edinburgh University Press Ltd. Hume, D. (1964) A Treatise of Human Nature. London: Scientia Verlag Aalen. Locke, J. (1961) An Essay Concerning Human Understanding. London: J.M. Dent & Sons Ltd. Plato (1997) Cratylus (trans. Reeve, C.D.C.). In Cooper, J.M. (ed.) Plato Complete Works. Hackett.