In doing metaphysics, understood broadly as an inquiry into what some sort of thing is, there are at least two approaches. One is to say, “well, I have this intuition about the way things are, and so here’s an argument to support it.” A lot of continuity of identity theory works this way. We say, “ok, I’m the same person now that I was last week and last year. How is that so?” And then we look for criteria of sameness.
Another approach is to say, “well, I have this intuition about how things are. I wonder if there’s another way to look at things?” This latter approach is a way of adding perspectives. It’s also the heart of discovery. If, for example, Copernicus had just kept adding epicycles, he’d have a much less interesting result. And if Heisenberg had just fudged some numbers to make sure that things were determinate all the way down, we’d be in a far less interesting world. Each had to give up on a common intuition, instead of working to find an argument to support it.
But I think in philosophy, since we’re not going to solve our problems by encountering some object in the world, it’s not exactly like discovery. That is, while observation of the stars and planets has ultimately made it pretty clear that the earth and the planets orbit the sun, there’s no observation which will tell us for sure if I’m the same person now that I was when I was five, or if I’d be the same person after undergoing fission or fusion. We just have to make a judgment on how we should apply terms like “same person” in these instances.
The approach that reaffirms our intuitions could be called “affirmation metaphysics:” I want to say that the person I see before me now is the same person I met forty years ago. So I need a sense of continuity of identity which allows me to apply “same person” to an entity who may bear no physical and few psychological traits in common with the being I met forty years ago.
The second approach is either “discovery metaphysics,” where I discover something about the world that I didn’t previously expect (“look, the earth orbits the sun!” “look, people don’t actually have selves!” “look, the world is merely a collection of phenomenal appearances!”) or “creative metaphysics.” The difference is whether I’m claiming that I’ve discovered this fact, or that I’ve produced a new way of conceptualizing things. Doing the latter is one of the most important tasks of philosophy; if there’s another way of looking at things, and that way is at least, or nearly as, well supported as the standard way, then we have a possibility of critiquing the standard way. So when Nietzsche reconceptualizes standard Christian notions of good and evil as “slave morality” and “master morality,” he provides a perspective that allows for a critique of those categories. Whether he discovered the truth about Christian morality, or simply shifted perspective in a way that presented a viable alternate interpretation, he still provides for a new way of looking , and a way that is not inherently incorrect (assuming it’s internally consistent and consistent with empirical facts). This is the heart of Nietzschean and, to some extent, Leibnizian, perspectivism, that is, the idea that we gain greater purchase on truth by acquiring the most possible correct ways of looking at something (though the thing we look at is not entirely consistent across perspectives; Nietzsche includes the morality of secular Europe as part of the “slave morality” that he’s critiquing, and he sees that as consistent with Christian ethics, whereas an older way of looking would have divided Christian ethics from secular, 19th century European ethics.)
An example: in “How To Count People,”* Mark Bajakian tries to write against the one-person-per-body view, doing some creative metaphysics. Centrally, his claim is that people with two-hemisphere brains (i.e. humans, and anyone else who has a brain structure like us) can and should be counted as two people at all points in time
if at some point in time the two hemispheres are split and (as in the many thought experiments on this topic) placed into separate bodies if they are the sorts of half-brains that could be split in two and still survive as two individuals (i.e. the kind of half-brains found in the thought experiments of Nagel and Williams.) Similarly, if two people are fused into a single thinking thing, that single thinking thing is actually still two people who are thinking the exact same thought at the same time (not just qualitatively the same thought; quantitatively the same).
Ok, I’m not sure I buy that. First of all, I’m not sure there is an answer to the question of how many people there are in fusion/fission cases, because our use of “people” and the way we count them developed in a world with no such cases, and the terms and concepts don’t come pre-packaged with ways to deal with that. So when facing such a case, we pretty much have to be creative.
If Bajakian thinks he’s discovered the truth about this, I think he’s mistaken; I think he’s putting forward a proposal for how we should count people. He certainly has an argument for it, but ultimately what he’s proposing is a convention for person counting. He thinks that this convention will solve a lot of conceptual problems (we don’t have the problem that occurs when, in a fission case, we are forced to say that the pre-fission person doesn’t exist anymore because he can’t be identical with either of his post-fission descendants since they are not identical with each other). But it’s not without its own problems: under Bajakian’s proposal, we have to say that some person who is exactly like any other single person is in fact two people because ultimately this person will undergo fission.
But here’s the interesting thing about that problem: it’s only a problem because that’s not the way we’ve been doing it. That is, it’s simply goes against an existing convention. Philosophers might say that it violates an intuition “we” have been doing it, with the “we” fairly loosely defined. Maybe “we” means “most people on earth,” or “people who share our culture,” or some such. But we (whoever this “we” is) could certainly imagine people who don’t count people the way we do, and if we could imagine a highly functioning society that counts differently, it’s not clear that we can come up with a strong metaphysical (much less empirical) reason that they’re wrong.
So if there is a people (and I think there might be) who counts someone as one person up to a certain point in time, and another after that point (this might be the case in cultures that have rites-of-passage to adulthood, for example, so that a person has a connection to, but is seen as importantly a different person from, his or her pre-rite-of-passage self), can we say they are wrong? In other words, what might be gained from something like Bakajian’s proposal, or learning about another culture that counts differently, or even reading, say, a novel that describes such a people, is that we can learn that our own method of counting is at least in part conventional. It might be bounded by certain natural limitations, but it’s probably not as absolute and fixed as it would seem. And simply appealing to an intuition about how to count people might count as no more than appealing to a cultural prejudice or a traditional way of doing things.
Bajakian, Mark, “How to Count People,” Philosical Studies (2011) 154:185–204