# Does the individual consciousness depend on the actual atoms or only on the configuration of the atoms? Suppose we have mastered cryo-freezing and atom-manipulation technology. We can freeze and unfreeze people at will. We freeze Sarah. We replace Sarah's atoms one by one. With all atoms replaced, we wake her up. Is it the "same" Sarah? (the same to herself, not just to us). Thanks, Mario

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...

# I was thinking, Is "absolutely nothing" logically possible? And I would just like to know what you would think of this argument. IF it is accepted that 1) "X is true if X corresponds to reality" then it would be logically impossible for "absolutely nothing" to exist. "Absolutely Nothing" implies no reality. If there is no reality then one can never say that "absolutely nothing" can exist, since "absolutely nothing" does not correspond to reality. But I ask you, if "absolutely nothing" is even possible. And if it is not possible, then what logical proofs are there. Thank you!

I'd like to take this question in a slightly different direction. I accept the point made by Prof. George: we don't need to think of the phrase "absolutely nothing" as referring to something; the logic of "There's milk in the fridge" isn't the same as the logic of "There's absolutely nothing in the fridge." But I'd like to pick up on a point in my colleague Prof. Levinson's reply: that if there being absolutely nothing is a possible state of affairs, then reality contains that possibility. Start by mulling over the idea that there being absolutely nothing is a possible state of affairs. A person might wonder: is a state of affairs something? Are there such things as states of affairs? How about possible states of affairs? If so, then so long as there is at least one possible states of affairs, there's not absolutely nothing. Now suppose -- as at least some philosophers seem to -- that for it to be possible that X, there must be a possible state of affairs in which X is true. This brings us to a...

# Does a proposition about the future have to be true today? If so does this preclude contingency and is every proposition of the future necessary?

Let's start with an analogy and see how far it gets us. Suppose I consider a proposition about some distant place. Suppose I consider the proposition that the population of Woodstock, New Brunswick (my home town in Canada) is over 6,000. [To keep things simple, assume that I mean the population today, August 5 2007.] I'm contemplating this "here" in Washington DC. But it's a proposition about some other place -- "there," not "here." And now consider the question: "Does this proposition about Woodstock have to be true or false here in Washington?" The question seems a little odd. What the proposition asserts refers to a particular place, but the idea that the truth of the proposition is, as it were, tied to the place where it's being contemplated seems off. We might put it this way: the proposition picked out by my use of the sentence "Woodstock has a population over 6,000" is true if the population of Woodstock really is over 6,000 and false otherwise. Asking if the proposition is true ...

# Space and time are measured in hours and metres, value is measured in utility. In these three fundamental scales, I have read that zero and the unit are arbitrary. I can see that there is no beginning of time, and no bottom to the universe and no absolutely valueless state of affairs, but it seems perfectly sensible to talk of two states of affairs being of equal value, in which case the difference in value would be zero. Two durations could be of equal length, as could two bodies. So is there a non-arbitrary zero in space, time and value that corresponds to the difference in length, duration or utility between the equally long, enduring or valuable?

It may be that there are two questions hidden here. You're right: if we can compare things in terms of length or duration or utility, then we'll sometimes be able to say that they're the same on this scale -- that if we subtract one value from the other, we get zero. But there's another question: is there such a thing as a thing's having zero length, taking zero time or possessing zero utility? Length and duration are not quite the same sorts of scales as utility. Length and duration are ratio scales. It makes sense to say that this stick of wood is twice as long as that one. Turns out that this goes with the fact that there is such a thing as having no length or lasting for no time. In these cases, we have a natural zero. However, it may not make sense to say that one thing has twice as much utility as another. Utility scales are interval scales. All that matters are the ratios of the differences. Let's make this a bit more concrete. I might rate the utility of a cup of coffee at 1,...

# Is it ever rational to commit suicide?

I would add this, however. While it certainly can be rational to commit suicide, people who are considering suicide aren't always in a good position to think about it rationally. That's for the obvious reason that many (perhaps most) people who are seriously thinking about killing themselves are depressed, and part of what depression does is make it hard to think clearly. A depressed person might believe that there's no hope, and that the pain will never end, but that's often not true. So yes: suicide can be rational. But if you know someone who's thinking about it, helping them get help may serve what they would understand as their own rational ends if only they were in a better position to see them.