1. SHOULD WE KILL HEALTHY PEOPLE FOR THEIR ORGANS?
Suppose Bill is a healthy man without family or loved ones. Would it be ok painlessly to kill him if his organs would save five people, one of whom needs a heart, another a kidney, and so on? If not, why not?
Consider another case: you and six others are kidnapped, and the kidnapper somehow persuades you that if you shoot dead one of the other hostages, he will set the remaining five free, whereas if you do not, he will shoot all six. (Either way, he'll release you.)
If in this case you should kill one to save five, why not in the previous, organs case? If in this case too you have qualms, consider yet another: you're in the cab of a runaway tram and see five people tied to the track ahead. You have the option of sending the tram on to the track forking off to the left, on which only one person is tied. Surely you should send the tram left, killing one to save five.
But then why not kill Bill?
2. ARE YOU THE SAME PERSON WHO STARTED READING THIS ARTICLE?
Consider a photo of someone you think is you eight years ago. What makes that person you? You might say he she was composed of the same cells as you now. But most of your cells are replaced every seven years. You might instead say you're an organism, a particular human being, and that organisms can survive cell replacement - this oak being the same tree as the sapling I planted last year.
But are you really an entire human being? If surgeons swapped George Bush's brain for yours, surely the Bush look-alike, recovering from the operation in the White House, would be you. Hence it is tempting to say that you are a human brain, not a human being.
But why the brain and not the spleen? Presumably because the brain supports your mental states, eg your hopes, fears, beliefs, values, and memories. But then it looks like it's actually those mental states that count, not the brain supporting them. So the view is that even if the surgeons didn't implant your brain in Bush's skull, but merely scanned it, wiped it, and then imprinted its states on to Bush's pre-wiped brain, the Bush look-alike recovering in the White House would again be you.
But the view faces a problem: what if surgeons imprinted your mental states on two pre-wiped brains: George Bush's and Gordon Brown's? Would you be in the White House or in Downing Street? There's nothing on which to base a sensible choice. Yet one person cannot be in two places at once.
In the end, then, no attempt to make sense of your continued existence over time works. You are not the person who started reading this article.
3. IS THAT REALLY A COMPUTER SCREEN IN FRONT OF YOU?
What reason do you have to believe there's a computer screen in front of you? Presumably that you see it, or seem to. But our senses occasionally mislead us. A straight stick half-submerged in water sometimes look bent; two equally long lines sometimes look different lengths.
Are things always as they seem? The Muller-Lyer illusion indicates not
But this, you might reply, doesn't show that the senses cannot provide good reasons for beliefs about the world. By analogy, even an imperfect barometer can give you good reason to believe it's about to rain.
Before relying on the barometer, after all, you might independently check it by going outside to see whether it tends to rain when the barometer indicates that it will. You establish that the barometer is right 99% of the time. After that, surely, its readings can be good reasons to believe it will rain.
Perhaps so, but the analogy fails. For you cannot independently check your senses. You cannot jump outside of the experiences they provide to check they're generally reliable. So your senses give you no reason at all to believe that there is a computer screen in front of you."
4. DID YOU REALLY CHOOSE TO READ THIS ARTICLE?
Suppose that Fred existed shortly after the Big Bang. He had unlimited intelligence and memory, and knew all the scientific laws governing the universe and all the properties of every particle that then existed. Thus equipped, billions of years ago, he could have worked out that, eventually, planet Earth would come to exist, that you would too, and that right now you would be reading this article.
After all, even back then he could have worked out all the facts about the location and state of every particle that now exists.
And once those facts are fixed, so is the fact that you are now reading this article. No one's denying you chose to read this. But your choice had causes (certain events in your brain, for example), which in turn had causes, and so on right back to the Big Bang. So your reading this was predictable by Fred long before you existed. Once you came along, it was already far too late for you to do anything about it.
Now, of course, Fred didn't really exist, so he didn't really predict your every move. But the point is: he could have. You might object that modern physics tells us that there is a certain amount of fundamental randomness in the universe, and that this would have upset Fred's predictions. But is this reassuring? Notice that, in ordinary life, it is precisely when people act unpredictably that we sometimes question whether they have acted freely and responsibly. So freewill begins to look incompatible both with causal determination and with randomness. None of us, then, ever do anything freely and responsibly.