What is truth, and how can we know that it is not an illusion?

Truth is a property that some propositions have and some do not. Itcan be hard to tell which a proposition is. But this much we can say.The proposition that Wittgenstein was Jewish is true if, and only if,Wittgenstein was Jewish. The proposition that Frege was Catholic istrue if, and only if, Frege was Catholic. And so forth. Somephilosophers (Paul Horwich, Scott Soames) think that's about all thereis to be said about truth. I'd disagree, but I hope we can all agreethat, even if that's not all there is to be said, it is something that there is to be said. (Note that there is some kind of sense herealready in which what is true depends upon how things are. For example,whether the proposition that Russell was German is true depends upon,well, whether Russell was German, and that's a question of how things are "out there".) So, that said, how can we know that truth is not an illusion?The obvious way to interpret the question is: How can we know, e.g.,that it isn't an illusion that it is true...

Hi, My roommate claims that it is impossible for an omnipotent being to exist. His logic is that if a being can create a rock so big it cannot lift it, then that being is not omnipotent because its lifting power is not infinite. But also, if it cannot create the rock so big it cannot lift, then it's creation power is not infinite. And because of this paradox, an omnipotent being cannot possibly exist. My boss was a philosophy major in school. He claims that this explanation is completely wrong. However, I do not understand his explanation as he said it very quickly and with many names of old philosophers and theorems and such that I cannot remember. So who is right? Regardless of whether or not an omnipotent being does exist or not, can one exist? Thanks.

This is a version of an old problem, one discussed endlessly by theologians. In its simplest form, it goes like this: Can God make a rock both big and small? Obviously not. So God isn't omnipotent. If you think that's a cheat, I'm with you. It's not possible for there to be a rock that is both big and small, so it's not limit on God's power that God can't make a rock like that. We have to be more careful in how we understand omnipotence. It's a delicate question how we should understand it, but a first stab might be: A being is omnipotent if, whenever it is possible that p, that being can bring about that p. The puzzle your roommate presents you is of this same form. If Fred is omnipotent, then it simply isn't possible for a rock to be so big that Fred can't lift it. So it's no limit on Fred's power that he can't create a rock that big. Of course, maybe Fred isn't omnipotent, and maybe it's not even possible for there to be a being that is omnipotent. But the argument your roommate offered does...

On the issue of gay marriage. What do philosophers think about the definition that politicians are suggesting should go into the constitution that marriage is the union between a man and a women? Is the definition valid?

Alex is right, I think, that people are not really debating what theword "marriage" means, though of course some politicians have beeninclined to bring out their dictionaries. What's at issue is, rather,what the institution of marriage is. It's like the difference between adebate about what the word "flower" means and a debate about whatflowers are. I think philosophers do have a contribution to makehere. Work in philosophy of language and mind over the last few decadeshas made philosophers very skeptical about the power and importance of"definitions". There are many cases to which one can point in whichsomething that was, at one time, taken to be definitive of somephenomenon or kind of thing is later taken not even to be true of it. It was, for example, once regarded as part of the "definition" of "mammal" that mammals give birth to live young. The discovery of the platypus upset that "definition", and so it is now not even regarded as true that all mammals give birth to live young. Similarly,...

I was reading Time magazine of August 15 of this year. I was curious about the fact about what would happen if natural selection is proved wrong? Then if it is proved wrong, is our understanding of the reality relative? And if it is relative, how are we sure that the way we understand our surroundings is the correct one? I really need you to answer this question because I am afraid of devoting my life to something that later will prove completely wrong. Thanks.

There have been many instances over the centuries in which well-confirmed scientific theories were later shown to be wrong. Usually, they weren't simply wrong. There was something they had right, but then it turned out that there were various sorts of problems, and a very different theory had to be introduced, often with a wholly different background metaphysics. Natural selection, as well confirmed as it now seems, could turn out to be wrong. (And there are very different takes on natural selection itself, anyway.) So yes, our understanding of the world is no more guaranteed to be correct than was that of our forebearers. (I'm not happy with the term "relative", which tends to be used in a different way.) But that doesn't mean that we don't have good reason to believe what we believe. We do. If we find we have better reason to believe something else, then we'll believe that. But until we do find better reason to believe something else, we should, well, believe what we have best reason to believe...

Question for someone religious probably: What is the significance of "faith," in religion? For example, why is the single most important thing in Christianity to have faith that Jesus is the son of God? Why wouldn't God let people just know all the answers?

I don't understand this question. First, I don't think "the single most important thing in Christianity [is] to have faith that Jesus is the son of God". It's true that there are many forms of religion that place a high degree of importance upon one's believing this, that, and the other thing, but I wouldn't claim to understand the attraction of such modes of living. And I really don't know what to make of the second question. Which answers is God supposed jealously to be hiding?

I am an atheist. If there really is a "god", why is there no physical proof that he, she, it ever existed? Except for written words ... which, for all that we know, could be all lies so people can feel better about themselves.

Are you supposing that, if something exists, it has to be possible to prove that it does? I would suppose not. So let us rephrase the question: Why isn't there compelling physical evidence that God exists? Some people think there is: The universe itself constitutes such evidence. And if that doesn't seem compelling, what would? The deeper question, however, is why one would suppose there had to be compelling physical evidence of God's existence. There is no compelling physical evidence, so far as I know, that there are such things as nondenumerable ordinal numbers. I suppose nonetheless that there are, and it seems odd to ask for physical evidence that there are such things.

In the past in places such as Greece, there were philosophers and scholars like Socrates, Plato, etc. Do we have any modern-day philosophers whose works are as highly regarded as the ancient ones? And were the works of the ancient philosophers, when they were alive, not regarded as highly as they are now?

This is a fun parlor game. I've often played it with friends andcolleagues. "Which philosophers active in the latter half of thetwentieth century will have their work read two hundred years fromnow?" The question can mean different things, and it's obviouslyimpossible to know. Our present sense of what was important in the workof the last sixty years or so may turn out to have been distorted byour own current interests. And things change. I've been told that ahundred years ago, Berkeley wasn't taken at all seriously. But he'sbeen a minor member of the canon for a while now. And people who doserious history of philosophy often read the work of many figures theywould themselves regard as "minor", because it helps them to understandthe environment in which philosophy was then being done. But it's clearenough what the intention of the question is: Are there philosophersaround now who have some claim to be members of the pantheon, up therewith Plato, Aristotle, Descartes, Hume, and Kant? With all...

I understand points as entities with zero extension. (Is this correct?) Yet infinitely many points are said to compose space. It seems like even infinitely many zeros could never add up to a finite non-zero value. So, what's up with points? If they don't have any extension, what are they? As a follow up, does it make sense to think about points in space in a different way from how we think about points in time?

Yes, a point has length, depth, and height zero. So do two points, three points, and even as many points as there are natural numbers. But if you have as many points as there are real numbers (of which there are more than there are natural numbers), then that set of points may have some positive length, depth, or height, though it may not. (In that case, they will not have zero length, depth, and height but may have no assignable length, depth, or height.) The branch of mathematics in which such things are studied is called "measure theory". Exactly what a point is is another question. In mathematics, points may be regarded in a wide variety of ways, as is convenient. Are there any points in space itself? That's a disputed question, and an empirical one, not one on which philosophers can pronounce.