In class, our professor discussed the impossibility of time travel. He stated that if in the future, machines are made to travel back into time, then we would be seeing people from the future right now. His argument ended there but would this be true? Is this a valid argument to disprove the possibility of time traveling in the future?

I hope your professor was just trying to provoke you, because it's a terrible argument. For one thing, it's not clear why he's so sure that we aren't already seeing people from the future, who've traveled back to this time zone, as it were, and are doing a good job of blending in. And in any case, suppose that in 3008, someone figures out how to travel backward in time. Why is it so obvious that they would come to this time?" Why not a later time? Or a time when there were no humans at all? If we add the plausible conjecture that the process would be expensive, dangerous and not altogether reliable, what basis would we have at all for speculating about the likelihood that someone would have shown up somewhere that we'd know about? More importantly, if something is actual , it's certainly possible, but the converse doesn't follow. Even if time travel is possible, it doesn't follow that it will ever actually happen. The world is and always will be pregnant with unrealized possibilities....

A friend argues that if a perfect God creates something different from himself, then it's necessarily imperfect, because, if perfect, it would still be God. So the universe implicitly entails evil and our universe is, if not exactly the best of all worlds, the least evil of all worlds. But then I ask: "Why did God create anything at all?" and my friend replies it's not his responsibility to answer that question and we end in deadlock. Is there any way to break the deadlock?

A further thought here: I think part of the issue has to do with the phrase "something perfect." Assuming it makes sense, to talk, for example, about a perfect piccolo (keys work flawlessly, correctly placed to produce notes that are in tune, etc...) Then I'd certainly agree with Oliver: nothing wrong with the idea that God could make such a thing. But this may not be what you're worried about, because presumably you'd agree that a perfect piccolo wouldn't be God. The point is that there could be a perfect thing of a certain sort that wasn't on that account part of God or an aspect of God, let alone identical with God. (It would certainly take an argument to show that nothing could count as a perfect piccolo unless it was God or an aspect of God, and I can't come up with a plausible one.) However, perhaps the question is whether God could create a perfect being in the sense of the phrase "perfect being" that's sometimes used, for example, in the Ontological Argument for God's existence. A perfect...

This site is a wonderful idea. Some of the questions seem to ask for moral advice, and I wonder whether the study of moral philosophy alone puts one in the position to give responsible advice. Wouldn't one have to know the person, the circumstances, and so on. And even then, in contrast to many kind of decision, moral decisions seem so personal as to rule out a right and wrong answer, which is not to say some actions and ways of living may be terribly wrong. What do you think?

I recall someone describing one of his colleagues, a well-know proponent of "rule utilitarianism," as "right in principle, wrong in practice." And more generally, I think you're right: being a capable ethical theorist doesn't make someone able to give good moral advice. I dare say every member of this panel can think of his or her own illustrations of this point. It's not just because the person and the circumstances matter; most every moral philosopher would agree with that. It's also that theoretical and practical skill are often not strongly correlated. To this we might add that experience, a feel for certain kinds of real-life details, and that elusive thing we call wisdom are all qualities we look for in people we seek moral advice from. That said, philosophers can sometimes help people think through certain kinds of issues for a couple of reasons. One is that they've often run into similar questions before and been part of extensive discussions of them. Another is that philosophers are often...

As far as I am aware most if not all religions promise the possibility of eternal happiness in the next life. However the concept of eternal happiness is impossible to understand. How could we be happy without our negative emotions - don't we enjoy our negative emotions sometimes (watching a sad or scary film)? Aren't our negative emotions a release? People who are happy for extended periods, e.g. people in-love or people suffering from mania cannot keep up being happy because it is exhausting and also people in these states become irrational. So why do we buy into the concept of eternal happiness in the next life so easily?

It's a nice question, and one that' s been discussed before in various versions. You've put particular emphasis on the idea that without negative emotions, we couldn't really be happy. Let's suppose you're right. As your own way of putting things suggests, it doesn't follow that there couldn't be such a thing as eternal happiness. The reason is that the kind of happiness that's at issue isn't best thought of as an emotion or mood but as some more global feature of our lives. In fact, your own point is that negative states can be part of, well, our happiness . We could also spend a bit of time on whether "negative states" that we enjoy (the frisson of "horror" we pay good money for at the movies, for example) really are negative states. But let that pass. I think the partisan of eternal life would probably object to being tied to the word "happiness." Some talk, for example, of "eternal bliss." But whatever state that's meant to pick out, it may not be quite the same as the one we...

I once read that "moral properties are causally inert". In other words, the fact that something is morally good or right doesn't make anything (or at least anything physical) happen or cease to happen. Only the fact that somebody BELIEVES that something is good or right does. My question is whether you think that this is specific to moral properties. For instance, aesthetical properties (like beauty) seem to be as inert as moral ones. And the properties of being money, of winning a game or of having an A as a school grade seem to me equally inert. Aren't they?

Let's start with money, which is also a good thing to end up with. Whether the piece of paper in my pocket is money isn't something that depends just on the intrinsic properties of the piece of paper itself. As someone once put it, the fact that something is money is an "institutional property." It depends on a complicated lot of social facts. Of course, if you BELIEVE it's money, I may be able to get you to part with your pet parakeet in exchange for it. And if you believe it's money, that's most likely largely due to non-monetary properties like shape, color, etc. And so someone might say: the monetary properties of the paper are causally inert. What does the causal work are its more metaphysically mundane properties. But that seems to slice things a bit too crudely. Even if monetary properties are "institutional" or "social" properties, the fact that the institution exists and that some things really are money has all sorts of causal consequences, and the fact that something really is money (has the...

No art exists but what man calls art, and man is partial. If this is true, and if it means that art is only valuable to men, and is thus immaterial outside of that context (the Human Context), then what is the true value of art-—the objective value? I would presume that it is valueless. Further, if an artist knows this, how can he still appreciate art, knowing it to be esoterically meaningful? …*Why* should he continue to appreciate art? --Darwin K.

Suppose I happen to get great pleasure from something that more or less no one else cares about. Maybe I really enjoy writing poems that avoid using the letter "p." I know that there's no cosmic importance to poems of this sort, and I know that it's just a quirk of my psychology that I enjoy writing them so much. This activity has no "objective" value if that means value from some point of view that doesn't take me into account. But it still has value for me , and as long as I don't spend all my time doing it, there's nothing irrational about my using this odd little hobby as a pleasant pastime. I don't need to be worried about the fact that in the larger scheme of things, "p"-less poems don't count. The point is more or less obvious, I hope: if I dont' need to be bothered by the fact that some things have value for me alone, artists don't need to be bothered by the fact that some things have value only for a wider circle of creatures: creatures with the sorts of cognitive and perceptual...

During discussions with one of my friends (who is an undergraduate biologist) we often enter into the empiricism vs. rationalism debate. In support of empiricism as the best route to true knowledge my friend often cites the many practical achievements made throughout history resulting from a scientific/empirical approach. In response to this I find it difficult to cite any significant advancements or examples of knowledge which can be credited to the side of rationalism. Indeed it seems to me the invocation of science's great 'utility' is often used as a defence of its (sometimes questionable) actions as well as its assumed superiority as a means to true knowledge. Therefore my question is how can one most effectively challenge science's monopoly on truth and knowledge (particularly in today's 'science worshipping society') in the face of its great practical achievements?

Perhaps we need to ask a prior question: why would we make such a challenge? And living in a country where large numbers of people are suspicious of evolution and think that people who worry about global warming or nutty or part of a conspiracy, I'm not so sure that society really is "science worshiping." If you want to know the truth about the natural world, science is your best bet. That's because "science" isn't a secret cabal, but most importantly it's a set of intellectual methods that let us explore the empirical world systematically, weed out unpromising hypotheses, and gauge the strength of likely explanations. Does acupuncture work for back pain? The answer may well be yes. But anecdotes aren't enough to make the case. We need the kind of systematic techniques that we call science. At the other end of the spectrum, how many dimensions does space-time have? We may never know for sure. But it's a safe bet that our best answer will come from science. And on it goes. If rationalism ...

hallo, I appreciate your homepage very much. I would like to ask you for opinion about a method of thinking. The idea is this one: If you have a question, and you think you cannot answer it, may you change your question to a similar/different one? For example: Does God exist? A similar question would be: How would it affect me if I knew that God does exist? (Example by: Bert Brecht- Stories of Mr. Keuner The question of whether there is a God A man asked Mr. K. whether there is a God. Mr. K. said: “I advise you to consider whether, depending on the answer, your behavior would change. If it would not change, then we can drop the question. If it would change, then I can at least be of help to the extent that I can say, you have already decided: you need a God.”) I think it means getting a different point of view or a different way to approach towards a question. What do you think about such a method of thinking? Is it legal or not? Do you think it is a serious way of thinking or is it a trap...

Perhaps the fact that I find this whole line of thought a little befuddling means that I shouldn't be answering the question. But maybe if I explain my confusion, that will help. Start with something simple. I might be curious about, say, some abstruse mathematical claim. And so I go to my mathematician friend and I say "Is it true that such-and-such?", where "such-and-such" is the mathematical conjecture I'm interested in. It would be pretty odd, wouldn't it, if my mathematician friend waxed "philosophical" about whether knowing the answer would change my behavior. In one way, of course, it would: I'd stop asking the question if I knew the answer. But in most other ways, life would go on as before. And yet, I still want to know whether such-and-such is really true. The point is that there really are two issues here, and it seems like confusion to mix them up. One is the matter of whether what I'm curious about is so; the other is the matter of what I'd do if it were -- or weren't. Now the two...

My younger brother, who is 13, is arguing that he will not go through any drastic changes in personality and mannerisms from now until the future and therefore a child is no different from an adult. I argued in the contrary stating that he will go through a lot of changes that might radically alter his outlook on life and personality. Is this correct or does it vary from person to person?

If I have it right, your brother thinks he won't change much, because he thinks that people in general don't change much from teen years to adulthood. He then goes on to draw a conclusion: children (or at least, teenagers) aren't really any different from adults. So we have two questions. First, is the premise true? Is your brother really right when he says that people who have reached the ripe old age of 13 are pretty much as they will be as adults? That's not a philosopher's question as such, though I don't think I'm going out on a limb when I say that many people change a good deal after they get past their teen years. But there's another question: even if we granted your brother his premise, what about his conclusion? It would depend, wouldn't it? It may be that people's basic personality (cheerful or prickly or inclined to fuss-budgetry...) is set by the time they reach their teen years. And it's pretty plausible that mannerisms are laid down early. But I'm guessing your brother thinks his...

Are necessary truths ultimately grounded in induction? For example truths of mathematics are said to be necessary, yet don't they make generalizations about an infinite set of numbers that are not verifiable; wouldn't this be considered induction? And if we ground our necessary truths on axioms, aren't these axioms theorems that a community has agreed to as being true and are not objectively true? Thanks for your answer, John

First, we need to set an issue aside. The word "induction" is sometimes used to refer to a certain sort of mathematical argument in which we prove something for every case by showing it for a "base" case and then showing that if it holds in the first n cases, it holds in the n+1th case. But it's pretty clear that your question is about induction as a matter of reasoning empirically from a limited set of instances to a claim about all cases, and so we'll use the word "inductive" in that way below. Here's an example of a necessary truth: every star that has planets orbiting around it is a star . Notice that it's universal; it says something about every star with planets. And if it were like "every star with planets orbiting around it is at least 3 billion years old," we could only show that it was true (assuming it is) by empirical means and thus, in a loose sense, inductively. (What we'd actually do is produce an argument from various theoretical and observational premises, but...

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