As I posted this, I saw that Donald had offered a similar reaction. But since I'd already written this up... It's a very interesting topic you've raised, and one on which philosophers have written a great deal. My view fall into the blunt, even philistine category, but I'll point to other views as well. Let's begin with your final question: is this worth getting worked up about? My answer is that it's not. What's at stake is whether some highly abstract, theoretical, and hard-to-settle metaphysical claims are true. Even if they are, life will go on as usual. You'll still experience things, remember things, look forward to things, make plans, carry them out, and in general live a human life. If there's some sense in which there isn't a single "person" that lives this life, the most psychologically healthy response is probably a shrug. You ask whether our consciousness continues while we sleep, or whether, on the other hand, it stops and restarts. One way to read that (probably not the best...

This is one of those cases where as long as we're clear on what we mean, there's not much of an issue. It would be perfectly in order to say "that creature existed two weeks ago; it was a chrysalis then." It's like saying that you existed lo so many years ago, though you were a toddler at that time. Leaving aside more radical doubts about identity over time, there's no problem with talking this way. If you say "that butterfly existed two weeks ago" and you mean something like "that creature, which is now a butterfly, existed two weeks ago" then there's nothing to worry about. But obviously if you mean "two weeks ago, this butterfly was around, as a butterfly," then you'd be saying something false. There are more subtler issues that a philosopher might raise, having to do, for instance, with whether the butterfly (or you, for that matter) is present at any one moment (as opposed to being a 4-dimensional being whose time-slices are present at various instants). But that question would come up even...

If I have it right, your brother thinks he won't change much, because he thinks that people in general don't change much from teen years to adulthood. He then goes on to draw a conclusion: children (or at least, teenagers) aren't really any different from adults. So we have two questions. First, is the premise true? Is your brother really right when he says that people who have reached the ripe old age of 13 are pretty much as they will be as adults? That's not a philosopher's question as such, though I don't think I'm going out on a limb when I say that many people change a good deal after they get past their teen years. But there's another question: even if we granted your brother his premise, what about his conclusion? It would depend, wouldn't it? It may be that people's basic personality (cheerful or prickly or inclined to fuss-budgetry...) is set by the time they reach their teen years. And it's pretty plausible that mannerisms are laid down early. But I'm guessing your brother thinks his...

Suppose there were a homunculus. Would it be like me? That is, would it have conflicting motives? Foggy beliefs? Occasional weakness of will? And while we're at it, would it make any difference if the homunculus were located in one compact region of the brain? Or woud it do just as well if it were distributed over different parts of the brain, and perhaps not even clearly confined to the brain alone? What would the homunculus have to be like to do the intellectual job that's at issue? And do we really need a lot of science to know that whatever we are, we aren't simple unities? An utter disunity isn't an agent. But think about the difference between my academic department and a random collection of professors. My department is made up of diverse individuals who don't always agree. But the department has a plan of organization, it deliberates and it acts. The members of the department co-operate to get things done, and the dissenters accept decisions of the department, once they're made, even if they...

Let's call the being that results from all this replacement Sarah2 . We can ask a pair of questions that seem different. One is whether Sarah2's conscious states will be like Sarah's. I agree with Mark that the answer to that question is yes; at least, it's hard to see why it would be no. But we can ask another question that seems to a different one: is Sarah2 the same person as Sarah? That's a lot more controversial. A comparison, based on an example by Peter van Inwagen: Suppose little Johnny builds a house from a small number of blocks and leaves it in the middle of the floor. And suppose that I come in and clumsily kick the house over. If I re-arrange the blocks in exactly the same way, then the house I assemble will be indistinguishable from the one Johnny built, but it's not so clear that it's literally the same house. And if I actually replace the blocks with new ones that are just like the old ones, then it's even less clear. So if we cryo-freeze Sarah, interrupting her normal...