For a reply to a very similar question, see http://askphilosophers.org/question/24944.

I'd say that they have different meanings. I interpret (a) as implying that your feeling better tomorrow is a sufficient condition (all else equal, presumably) for your going out, whereas (b) implies that your feeling better tomorrow is a necessary but maybe not sufficient condition for your going out. That is, (b) seems more cautious, more hedged: (b) allows that you may not go out even if you do feel better tomorrow. Compare: (c) If you feed your pet goldfish, it will flourish; (d) Unless you feed your pet goldfish, it won't flourish. Given how easy it is to overfeed a pet goldfish, (c) is doubtful: your pet goldfish may not flourish even if you feed it. Given that pet goldfish depend on being fed, (d) isn't at all doubtful.

All else being equal, "My dog ran around the block wearing a big purple hat and green trousers" is far-fetched and unlikely to be true. But I wouldn't classify it as absurd in the logical sense, i.e., as making no logical sense. On the contrary, I think I can imagine (i.e., mentally picture) that amusing scenario. Now, if you were to claim that your dog ran around the block wearing colorless, entirely green trousers, I would classify your statement as logically absurd in the sense that it's logically self-inconsistent: it's logically impossible for anything, including trousers, to be both colorless and entirely green. So I'd say that something like logical self-inconsistency is the mark of a statement that has crossed the line into genuine absurdity. It's great to hear that, at 16, you've already been studying philosophy. I hope you'll keep doing so!

The sorites problem is a paradox for the reason that any problem is a paradox: it's an argument that leads from apparently true premises to an apparently false conclusion by means of apparently valid inferences. I don't think it's fundamentally a problem of definition, because the concepts that generate sorites paradoxes would be useless to us if they were redefined precisely enough to avoid sorites paradoxes. Take the concept tall man . In order to make that concept immune to the sorites, we'd have to define it in terms that are precise to no more than 1 millimeter of height, because a sorites argument for tall man exists that involves men who differ in height by only 1 millimeter. But defining a tall man as (say) a man at least 1850 millimeters in height would mean that in many cases we couldn't tell whether a man is tall without measuring his height in millimeters. Given the impracticality of taking such precise measurements in the typical case, we'd likely stop classifying men as "tall" and ...

I'd say that in many cases there's indeed a difference between grasping a proposition and believing the proposition, i.e., believing it to be true. To take a well-known example from mathematics, Georg Cantor believed that the Continuum Hypothesis is true, whereas Kurt Gödel believed it's false. Both were brilliant mathematicians; I see no reason to think that their disagreement arose from either man's misunderstanding the proposition in question or some related proposition. But not all cases are like that. Consider the proposition that all bachelors are unmarried. Anyone who fails to believe that proposition, I'd say, fails to grasp it, because grasping the proposition implies believing the proposition. At any rate, I can't make sense of the idea that someone could grasp that proposition without believing it.

I think so. Consider the example you gave. A's selflessness (her generosity, anyway) is manifested by her sending the money to B, whether or not B ends up accepting the money. Now, if A somehow knows that B will return the money immediately and is counting on B to return it, then A's selflessness is only apparent rather than genuine. But otherwise, I see no reason why A's action can't be considered genuinely selfless, whether or not the recipient in fact keeps the money. Further, I see no reason why C must be deemed selfish just because he accepts the money: it might be that, through no fault of his own, C desperately needs the money. What I think genuine selflessness does require is scarcity: if a particular resource is available to all in unlimited supply, then no one can genuinely make a gift of that resource, let alone a selfless gift. So I don't think there can be selflessness in heaven, if heaven is as it's described by various religions.

At least 33, to judge from the Areas of Specialization (AOS) listed here: http://philpapers.org/surveys/results.pl. Less facetiously: There's no non-arbitrary way to give a precise answer to your question, just as with the question "How many branches of science are there?" Careful attention to language is essential because, among other things, only when we're careful about language can we tell which philosophical problem (if any) we're trying to solve or which philosophical question (if any) we're trying to answer.

I don't think there's a deep puzzle here, as I hope I can explain. The kind of possibility that stems from uncertainty is usually called "epistemic possibility," often signaled in English by "may" or "might," as in "There may [or might] be life on other planets." We're far from certain that there isn't life on other planets, so there may [for all we know] be life on other planets: life on other planets is an epistemic possibility for us. There are other kinds of possibility, such as metaphysical possibility, but I think the general point I'll make applies to all of them. To deny possibility in this sense, to say that some state of affairs S isn't epistemically possible for someone, is roughly to say that he/she is certain that S doesn't obtain, or at least he/she knows that S doesn't obtain (if knowledge doesn't require certainty). So I'd say that, right now, my own non-existence is epistemically impossible for me, because I know (indeed, I'm certain) that I exist, for the reason Descartes gives...

I'm intrigued by your suggestion that there may be a paradox here, but I'm having trouble reconstructing your reasoning. As far as I can tell, your reasoning relies on the premise that any definition must contain whatever it defines . But I'm not sure that premise is plausible. Merriam-Webster.com defines "walrus" as follows: "a large gregarious marine mammal ( Odobenus rosmarus of the family Odobenidae) of arctic waters that is related to the seals and has long ivory tusks, a tough wrinkled hide, and stiff whiskers and that feeds mainly on bivalve mollusks." That definition (more precisely, the definiens ) doesn't contain the word ("walrus") being defined, which is good: otherwise the definition would be unhelpful. Nor does the definition contain a walrus; we'd need a cage to do that. Instead, the definition gives us a string of words meant to pick out the walrus from among other things. If it's a genuine definition, then the principle on which it seems you're relying is false. But I may...

Why is this question so compelling? (to someone, anyway) Charles Taliaferro posted a thoughtful answer/challenge to the same question just three weeks ago: http://askphilosophers.org/question/24944