How do philosophers decide where to draw a distinction between what one "has" and what one "is". That is to say, am I the same "I" that existed before I lost a toe, or a leg, or the rest of my body, or even my brain, my mind, my thoughts, my self? Is it not logical to say that what is "me" must be distinct from what is "mine"? If this is not true, then would not "I" exist only in a virtual sense, as the image or focus of all "my" possessions?

This is a good quesiton and one that philosophers disagree about. There are three sets of issues to consider.

One is how to make sense of the persistence of anything through any change whatsoever. For example, if a tomato ripens and turns from green to red, is it the green tomato the same tomato as the red one? How can that be if one and the same thing cannot be both red and not-red? Are there some properties of an object that can alter without destroying the object, and others not? How can we make sense of that?

The second set concerns change of parts. Consider a statue and a lump of clay. It seems that the statue just is the lump of clay shaped in a certain way. But if the statue loses an arm, it seems that it is still the same statue, but it isn't the same lump of clay. Or suppose we replace the arm with one molded into the same shape out of different clay. Again, it seems that the statue can survive such a change, but the lump of clay that is the statue is not the same as the original lump. (You can ask this question also about things that aren't artifacts, e.g., over a person's lifetime their heart changes in the cells that make it up, but it continues to be the same heart.)

The third set concerns the specific problem of the identity of persons. On one hand persons seem to be just living human bodies: my existence is exactly co-extensive with the existence of this living body. But on the other hand it seems that sometimes persons go out of existence before their body dies. We also find it tempting to say of persons who go through radical psychological changes (perhaps they have amnesia or a radical conversion) that "they aren't the same person". And some find it possible to imagine that they could exist without a human body if their mental life (including their memories and other psychological traits) were transferred to another kind of body. (This idea seems to be popular in movie and tv dramas in which persons enter the body of a dog.) So it is tempting to draw the conclusion that persons are not just living human bodies, and their identity should be understood in terms of psychological continuity.

You ask, though, how do we (philosophers) resolve these puzzles? The usual way is to consider what assumptions seem to give rise to the conflict in our beliefs about the persistence or identity of something. For example, in the case of persons, we find it tempting to believe both that persons just are living human bodies, and also that persons can exist without a living human body and also a living human body can exist without it being a person. The question, then, is whether there is a way to interpret these beliefs so that they don't conflict (although they seem to), or if not, which of them we should reject.

The basic method is to look very carefully at the beliefs that seem to give rise to the puzzle and to figure out which of the beliefs (or which interpretation of them) is really important to preserve. There may be various reasons why we want to preserve a belief, e.g., it might be that we have very good empirical evidence for it. Or it might be that it plays an important role in our thinking about morality or law. Once you've carefully selected and defined the really important beliefs, see if the puzzle remains. If it does, look again to determine whether the beliefs can be adjusted in ways that preserve what is important about them, but also avoids contradiction with the other important beliefs.

I'm sure this seems very abstract. But in the sort of case you describe, I think some changes in persons are changes in properties that can be handled by being sensitive to time and tense: I was shorter when I was a child than I am now. Other changes (like losing a toe or a leg) are perhaps similar to the statue and the lump of clay: I am more like the statue (or the heart) than the lump. And changes so drastic that they involve a loss of mind are ones we don't accept because the notion of a person is partly a forensic notion, i.e., concerned with responsibility. If what is important about persons is that they are agents in the world that can be held responsible for their actions, then to say that something is a person but has no mind undermines the very point of having the concept of person at all. Or, if this isn't what's important about persons, your task is to figure out what is.

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