EM: Oh, I'm so depressed! I've been alive for 342 years and I've had enough of it! I have this elixir that will cause me to live for three hundred more years – and forever if I continue to drink it – but I can't bring myself to drink any more. There's nothing I want except to die.

BW: I can see why you might be depressed, Elina. It appears that you've exhausted all your deepest desires – what we might call your categorical desires – and now there's simply nothing to sustain your interest in life. Life has become meaningless for you because you've fulfilled all the projects you desired to fulfil.

EM: I think you might be right, but what do you mean by ‘categorical desires’?

BW: Categorical desires are the desires that give us a purpose for living and, correspondingly, a reason for resisting death and regarding it as a bad thing. Some desires are merely conditional upon our remaining alive. For example, our desires for basic necessities such as warmth and shelter are like this. If we die, it makes no sense to say that these desires have been frustrated by our dying; the desires simply die with us. But in the case of a categorical desire, if death intervenes before the desire is fulfilled, then the desire has been frustrated by death. Most of our desires are of this kind. An example would be my desire to finish the book I'm working on; if I were to die before the book is completed, then my desire will have been thwarted.

EM: And you think my problem is that I've completed all the projects I wanted to fulfil, and I have no more categorical desires left.

BW: Yes, that's right. And I don't think this is merely an accident; there's nothing unique about you. I think it's a necessary feature of the human condition that our categorical desires are finite. If we live too long, then we'll inevitably get bored with life. Although it will be sad to lose you, Elina, the only rational thing for anyone in your position to do is to refrain from drinking any more of the elixir.

JF: Hold on a minute, Bernadette! That sounds like rash advice to me. Why should we suppose that Elina's categorical desires have been exhausted? Clearly, Elina is going through a bad patch, but it seems perfectly plausible to me that certain of her categorical desires could be renewed. Indeed, I think we should distinguish between two kinds of categorical desires: there are some that are exhaustible, but there are others that are renewable and need never be exhausted. This is because certain of the pleasurable experiences that we desire to have can be repeated over and over again without losing their appeal.

EM: This sounds hopeful. Can you say more about the distinction you've just made?

JF: Yes, certainly. Some of our categorical desires are exhaustible because they are desires for experiences which, once had, have fulfilled their purpose. So, for example, I once had a desire to run a marathon; I wanted to prove to myself that I was self-disciplined enough to train for it, and complete the race without collapsing along the way. I succeeded, I'm pleased to say; I brought that project to fruition, and hence my desire was fulfilled. Then I no longer had the desire; it had been satisfied. Of course, I might regain a desire to run a marathon, but it would no longer be a desire to prove that I could do it, so it would be a different desire. Other categorical desires are not exhaustible in this way, however. For example, I enjoy good food, listening to music, going to the theatre, spending time with my friends, making love to my wife – all of these are repeatable pleasures, and they can refresh our categorical desires indefinitely.

EM: Do you mean that desires for these repeatable pleasures can never be satisfied?

JF: Well, they can be temporarily satisfied; but they are such that they are liable to be refreshed after a while. When I've had a good meal, for example, my desire for that form of enjoyment has been temporarily, but not finally, satisfied; the desire will re-emerge at a later time. As I see it, these renewable desires are capable of endlessly sustaining our interest in life.

EM: But if that's true, why has all the zest gone out of my life – why have I become so profoundly bored?

JF: That's not an easy question to answer. It could be, as I suggested earlier, that you're just going through a bad patch. Even people like me, who are very unlikely to live for hundreds of years, sometimes get bored or depressed; we feel unable to enjoy the things that had previously given meaning to our lives. Some of these people never manage to overcome their depression, and it is possible that you are one of those unfortunate people. However, what I'm saying is that there's no reason to suppose that life must become intolerably dull, and hence it would be unwise of you to refrain from drinking the elixir.

EM: You may be right, Jim. I can imagine that I might, at some point in the future, regain some interest in life; so perhaps I should take another dose of the elixir. But now I start to wonder whether this could, as you suggest, continue indefinitely. When I reflect upon my life up till now, it seems to me that Bernadette is right – our categorical desires must run out at some point.

BW: Perhaps we need to recognize that there are two distinct issues here. Firstly, there is your immediate predicament, Elina. What is most urgent for you to determine is whether you should drink any more of the elixir, which will give you another three hundred years. Secondly, there is the longer-term question of whether an unending life – a temporally immortal life – is a desirable thing. If the answer to this second question is ‘yes’, then your problem is solved – you should drink the elixir, and you should go on drinking more of it after each three-hundred-year interval. If the answer to the second question is ‘no’, however, it then still remains to be determined whether another three hundred years would be good for you.

JF: You are right to distinguish those two issues, yet I remain convinced that an immortal life is a desirable prospect. There is no reason to believe that all of our categorical desires will reach a point of final burn-out.

EM: I don't see how you can be convinced about that. I'm having extreme difficulty even imagining an immortal life. I can just about imagine what it might be like to live for another three hundred years, because I've already lived that long. Although I cannot predict how human society and the world as a whole will evolve, I can picture to myself a range of different possible scenarios, and imagine what each of them would be like to live through. When I try to imagine immortality, however, my imagination is stretched beyond its limits. For a start, the planet earth would have to go on forever without collapsing into the sun, otherwise there would be nowhere for me to live. But this would mean the physical laws that govern our solar system, and the universe as a whole, would have to be different than they are.

JF: Not necessarily. You could build into your imagined scenario the advancement of space travel, to such an extent that, when the earth begins to die, you simply fly off to another inhabitable planet. And you move from one planet to another throughout the ensuing millennia.

EM: But would I be on my own, or with other people? I couldn't bear to be all alone; yet I'm not sure there is anyone with whom I could bear to spend eternity either.

JF: Imagine a mixture – sometimes you could be on your own, and sometimes with other people, and these would always be people that you get on with.

EM: Maybe your imagination is better than mine, Jim. I've already reached a point where I cannot say whether immortality is desirable or undesirable, because it's not at all clear to me what I'm supposed to be imagining. It seems that, if we keep our imaginations tied to the facts about the world as we know it, then we fail to imagine a genuinely immortal life, yet if we allow ourselves to mould the facts in whatever way we please, then we lose our grip on what we are imagining, and we don't know what to say about it.

BW: I think you're right to be wary of giving free rein to the imagination in this sort of case, Elina. Jim's approach to the question of the desirability of immortality is paradoxical. He highlights features of our ordinary mortal lives which we typically find enjoyable and desirable, and points out that at least some of these features are amenable to repetition. Although this seems plausible, he then assumes that the relevant features of a mortal life can be smoothly imported into an imagined situation wherein one is supposed to be immortal. This is paradoxical because, as you've already discovered, the sort of world that we are obliged to imagine when we try to imagine an immortal life is one radically different, perhaps indeterminately different, from the world in which we live; and we cannot simply assume that enjoyable features of a mortal life in our world would remain enjoyable if they were features of an immortal life in a radically different world.

EM: I'm not sure whether I'd say Jim's approach is paradoxical, but there's certainly something fishy about it. Perhaps the problem I have derives from the impossibility of imagining a completed immortal life. If I can't imagine the life as a whole, then I can't say whether the life as a whole is desirable; and if I can't say whether the life as a whole is desirable, then I cannot reach a verdict on whether it is the sort of life I desire to live.

JF: I admit that it's impossible to imagine a completed immortal life, because, by definition, an immortal life is never completed. But I don't see why you should need to imagine the whole life in order to determine whether immortality is desirable. All you have to do is imagine a life wherein, on any given day, there is always another day to come. If you find that prospect desirable, then you are, in effect, finding the prospect of an immortal life desirable.

EM: I must say that, when I think about it, I do not find that prospect desirable at all. Indeed, were I to be living a life which could not have a final day – that is, were I to be condemned to go on and on, day after day, with never an end in sight – I'm sure I would feel even more dreadful than I do now. At least, in my current predicament, I don't have to make an all-or-nothing choice between ending my life now and never being able to end it. As things stand, every three centuries I am able to review my options, and make a reasonably well-informed choice about whether a further three centuries would be desirable.

BW: It sounds, then, as though you're feeling a bit less despondent about your plight than you were earlier, Elina.

EM: Yes, that's true. I can see that, in some ways, I've got the best of both worlds: I can let myself die if I want to, or I can live on as long as I wish, without ever having to decide whether I wish to live forever.

BW: Of course, if it really is the case that your categorical desires have been exhausted and, despite what Jim says, are never to be renewed, then by taking another sip of the elixir you will be condemning yourself to three hundred years of utter misery.

EM: Yes, I'm aware of that.

JF: But, believe me, you're bound to get over this dismal period – something will come along to re-ignite your joie de vivre.

EM: Hmm, I don't know. I've still got a few more days to go before the effects of the previous dose of the elixir wear off. Thanks for your advice, both of you, but I'm going to have to go and reflect again on my predicament.