A man has murdered someone and has been executed legally in the US. If I could go back in time and kill the killer before he committed his crime, thus saving the life of his intended victim, would this make me a murderer, or his executioner, as I would be killing him before he had committed his crime? This question is from Anthony Roddy-Burns in Rochdale, England.

One's tempted to say that if the man has indeed murdered someone in the past, then if you were to travel back in time you could not kill him before the murder. The past is past and, contrary to Hollywood lore, it cannot be changed. For more on this, see Question 242 .

Is the scientific method anything more than a good algorithm?

People often speak of "the scientific method", but it means nothing.There is no such method -- and one proof of that is the greatfascination and challenge scientific inquiry holds for so many people,something it would not have if its practice merely consisted in turningthe crank of The Method. However, the myth persists and it not onlygives a false picture of science, but also encourages the thoughtthat science and philosophy are very different kinds of enterprises.There are differences, to be sure, but they don't consist inphilosophy's not yet having found its method.

Why did you take philosophy? Was it a long standing goal in life or did you just wake up one morning and decide to be the next Plato or Socrates?

For many, I expect, a love of philosophy was neither a revelation nor something nurtured since infancy. Like many of the better things in life, philosophy is something one develops a taste for, over time, often accelerated through exposure to powerful influences at critical junctures. A mind-bending book here, a wonderful teacher there, some deeply satisfying experiences trying to wrestle with a problem, and before you know it, it's under your skin.

Why is human life valued more than animal life in the absence of religion? Are arguments based on our being intelligent or sentient valid, after all we make the rules. If you could ask an elephant it might offer other criteria to value species by.

According to some ethical theories that make happiness the central touchstone of morality, for instance utilitarianism, human happiness should not count more strongly than happiness in the non-human animal world. One quantum (as it were) of human happiness should contribute as much to the grand calculus of pleasure as does one quantum of rat happiness. Now, it may be that humans are capable of more happiness than rats; or perhaps, as John Stuart Mill argued in his Utilitarianism , they are capable of a kind of happiness that is of greater value than any happiness a rat could experience. But that's not to privilege humans; it's just to acknowledge a fact about their greater capacity for happiness. You wonder whether this might be unfair, because you wonder whether, if an elephant had written Utilitarianism , the theory would have looked a bit different (say, assigning great value to distinctively elephantine pleasures). But this is an impossible road. We are human, we are who we are,...

Socrates said, "All I know is that I know nothing". What I'm trying to figure out is this: if I know NOTHING, how do I KNOW that I know nothing? It just goes round in circles thus becoming nothing more than a paradox. Would you agree?

Can we really defend Socrates here though? (Note: It's early Saturday morning and this is relevant to present fearless wading into rough waters.) He says that he is "likely to be wiser" by virtue of not asserting that he knows something worthwhile. But isn't wisdom knowledge? Doesn't being wiser require knowing a little more? If so, then it seems that Socrates really is saying that he knows that he doesn't know anything worthwhile. (That's the knowledge that makes him just a tad wiser.) And now we're back to worrying whether Socrates' assertion is paradoxical. I can imagine two responses: (A) one might claim that one's failure to know anything worthwhile isn't itself a worthwhile thing to know (and so Socrates' claim to knowledge doesn't clash with what he claims to know, viz. that he knows nothing worthwhile). Or (B) one might hold that one could be wiser simply by failing to claim knowledge that one doesn't have (so we can make sense of Socrates' claim to being slightly...

According to Descartes' demon hypothesis, would it be possible for the demon to deceive us about the rules of logical inference e.g. could my belief in the law of non-contradiction be caused by the demon?

Again, this awaits a Descartes scholar, but what Descartes says in his "First Meditation" is this: Andbesides, as I sometimes imagine that others deceive themselves in thethings which they think they know best, how do I know that I am notdeceived every time that I add two and three, or count the sides of asquare, or judge of things yet simpler, if anything simpler can beimagined? So it seems Descartes argues that, as far as we can tell by the end of the "First Meditation",we could be wrong about (and so can't be said to know) basiccomputational facts, wrong about (what philosophers often call) analytictruths (like "A square has four sides"), and even wrong about "yet simpler"matters (like logical laws, perhaps).

If, as George Washington said, "All government is force," is not resistance to government a necessary and morally superior corollary to resistance to force in general?

That may be a corollary to the general claim that one ought to resist all force. But is the general claim true? Presumably, the thought behind the general claim is that all force is morally wrong and so resistance to it is morally permissible if not required. But is all force morally wrong? This is one way of casting the central topic in political philosophy: whether, and if so under what conditions, the state could have the right to use force over individuals to compel compliance with its commands. Anarchism takes the answer to be No. Utilitarian and social contract approaches believe the answer is Yes: under certain conditions, the establishment of a state that wields power over individuals can be justified. (See Question 452 for some references.)

When you get past the rhetoric on 'most convincing arguments and logical reasoning', are people's preferences for a certain type of philosophy merely subjective 'taste'?

I don't think it's rhetoric. Philosophers (and people generally) dochange their positions on the basis of the arguments. Maybe you thinkit should happen more often than it does. But theforce of arguments is one that makes itself felt regularly inphilosophy. That said, I think there is something to the claim thattaste plays a role inshaping the kinds of problems, answers, arguments, examples, etc. thatappeal to a philosopher. But why the deflationary "merely subjective"?Certainly, the importance of taste isn't felt just in philosophy; it's felt as well in the natural sciences and mathematics (not to mention most other human pursuits).

Is there a way to prove reincarnation? Has the possibility been explored?

(1) Only mathematicians and logicians are in the business of proving anything, and I don't think reincarnation is a hot topic for them. (2)Scientists offer evidence for their claims, making them more or lessreasonable to believe. But before that can be done, one has to make theclaim quite clear and, ideally, quantifiable. It's hard to offerevidence for or against a claim whose content is rather obscure. I saythis because when people talk to me about rebirth or about souls'moving from one body to another, I don't really understand them. I get confused enough when I think about the relation of my mind to my body!