Tricky question, but I'm inclined to say no. If you were your sister, what would have happened to her? I think she and you would have to be the same person. But I don't think two people could have been one person. (It's not like Clark Kent and Superman. That is one person in a situation where it is wrongly thought (by Lois Lane, anyway) that there are two people.)

Suppose I know that half the time the sea is calm, half the time it is very rough. If I send you out in a rowboat without checking the weather, my act is immoral, even though I am ignorant of the consequences. I would say that the case of someone who believes that God will protect his child from a road accident is different: it's error, not ignorance. Here the moral situation may be more subtle, since we may hesitate to blame people who are acting sincerely on the basis on their beliefs, even if we are convinced that their beliefs are incorrect. But I'm inclined to say that there can be cases where there is a kind of willful ignoring of the evidence that leads to moral culpability.

We all believe that mental processes influence physical outcomes. For example, right now my mental processes are (I hope) influencing the movement of my fingers on the keyboard. How is that possible? Well, if mental processes just are physical brain processes, then there is no special mystery. If on the other hand they are non-physical, then there may be a special problem in seeing how such different sorts of things -- the mental and the physical -- could be causally related. But I'm not even sure there is a special problem in this case. It's difficult to understand causation even in the simplest physical-physical case, but it is not clear that a big difference between cause and effect raises a special additional problem. After all, those moving fingers of mine are causes all sorts of changes to the world wide web, a digital realm very different from my digits. It's true that the expressions 'the power of positive thinking' and 'self-fulfilling prophecies' are cliches, but it seems...

Astronomers study the stars; philosophers of science study the astronomers. And just as astronomy is worthwhile even though it does not improve stellar behaviour, so philosophy of science may be worthwhile even if it does not improve the behaviour of astronomers. Some scientists have nevertheless been influenced by philosophy. In the history of science, giants like Galileo, Newton, and Einstein come to mind in this connection. And some current scientists probably also come under the influence of philosophical ideas, for example Karl Popper's idea that it is important to think about negative evidence, about what sort of data would show that your hypothesis is wrong. Philosophical influence on science may be beneficial, but one shouldn't exaggerate the case. For quite generally there is a big difference between being good at describing a practice and being good at doing it. For example, it's one thing to be good at coming up with hypotheses and testing them, quite another thing to be good...

I agree that a lucky guess is not knowledge. It's a true belief, but what seems to be missing is some justification for the belief. What is more surprising is that even a justified true belief may fail to be knowledge. Do you know what time it is right now? Have a look at your watch. Now you know, because you are justified in believing that your watch is working. Of couse if unbeknownst to you your watch has stopped, then you you don't know the time, because your belief about the time, though still justified, is false. But now suppose that, by sheer coincidence, your watch stopped exactly twelve hours ago. In that case your justified belief would be true! But still, you wouldn't know what time it is. Hey presto: that's a justified true belief that is not knowledge. Cases like these were brought to the attention of the philosphical world by Edmund Gettier in the 1960s, and they have prompted a large literature. For an article on Gettier cases, click here .

For a machine to have knowledge, it looks like it has to be able to have beliefs, since when you know something you also believe it (though not conversely). And for a machine to have beliefs, it has to be able to form representations of how the world might be. So the answer to your question will depend in part on whether machines can form representations. This is a hotly debated question in the philosophy of mind, for the case where the machines in question are computers. The two most famous arguments are due to Alan Turing and to John Searle. Turing argued that there could be a computer that is able to engage in an extended intelligent conversation (by email perhaps) so good that it fools people into thinking it is a person, and that such a computer ought to be taken to have representational states. Searle argued that since we know how computers (traditional ones, anyway) actually create their end of the conversation, and that this involves only registering the electronic equivalent of the...

A belief can be irrational, if you don't have a good reason for it. Can a fear be irrational? It seems so, if it based on an irrational belief. Thus to be afraid of ghosts is irrational. But I think you are asking whether it is irrational to fear something which, though based on a perfectly rational belief, is just something you can't do anything about. And here I am less sure that we should say that the fear is irrational. Impractical, perhaps, but irrational? Maybe it is helpful to compare this to something good that you can't do anything about. Suppose you know that, whatever you do, your parents are going to get you something you really want. Is it irrational to look forward to that? It seems not. But if it is not irrational to look forward to something good you can't do anything about, then why is it irrational to fear something bad that you can't do anything about? Maybe these two cases are importantly different. Looking forward to something is pleasant, so there is no...

I suspect that many of us suffer from your incoherent-footnote-to-Plato worry from time to time, but let me say two encouraging things. The first is that although philosophy does often circle back to issues and arguments in its own history, when we consider them anew we consider them in a new context, and this makes room for originality. Of course it helps not to expect too much. You don't have to provide a definitive reply to scepticism about the external world: it's glory enough to push the discussion along in smaller but still productive ways. The second encouragin thing to say is that originality isn't everything. Even if it turns out that someone else had the idea centuries ago, working things out for yourself has a special intellectual value for you. Philosophy is not a spectator sport.

It is very difficult to see how free will is possible. The problem your second view raises looks like the problem of determinism. If everything that happens in the world, including all human actions, are determined the laws of nature, then it is indeed difficult to see how we can have free will. Now maybe the laws of nature do not completely fix every event, but only the probabilities of various events occurring. Indeed this is the standard understanding of quantum mechanics, which you mention. But even this 'slack', this element of indeterminism, does not seem to leave any room for free will. If my body just happens to go one way rather than another by chance, that is not me acting by my own free will, since I am not in control. The first view you mention is rather different. This is the thought that we have no free will if God knows everything we will do. In my view, this idea of foreknowledge is less of a threat to free will than determination by law. For even if someone knows exactly...

This is what David Hume's great skeptical argument seems to show. The claim that nature is (and will be) uniform, or such that our inductive practices will tend to take us to the truth, is itself something that it seems we could only know by using induction, but to use induction to justify induction seems worthless. For my money nobody has yet given a fully adequate reply to Hume's argument. And if his argument is sound, the our reliance on induction does seem to be a matter of faith: something we believe though we can have no good reason for it. As you probably know, there is a huge literature of attempts to solve the problem of induction. My own view is that the prospects for inductive justifications of induction are better than they first appear. For example, I think that the fact that a particular method of predictive the future has worked well so far can give some reason to trust it in future, even though that argument would of course have no force for someone who refused to use induction...