Haven't you answered your own question? Something that is clear just isn't any color, any more than the air is some color (usually!).

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...

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...

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,...

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...

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?

Have you ever had a dog or a cat? Most people find that it is possible to communicate with their animals to some degree. And plausibly, language grew out of much more primitive forms of communication.

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.

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...

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.