Why is it so easy to define "island" and so difficult to define "dog"? Both terms refer to quite "natural" and well-known things. We can say that an island is an area of land surrounded by water, but we can't say, for instance, that a dog is an animal that barks, since a sick dog that can't bark is still a dog. It is also curious that we all know what a dog is without knowing the zoological definition of this species. Is there a name for this difference between the two words?

I'm a little bit worried about Australia, but let's leave that continent to one side. Sometimes what makes something a particular kind of thing is a set of superficial properties, while in other cases the relevant properties are less obvious. Island is in the former group, dog is the in the latter. Presumably what makes something a dog has something to do with its genetic makeup, not superficial properties like its bark. In a way, this is surprising, since we talked about dogs before we know anything about genes, and even today I talk confidently about dogs without knowing how they differ genetically from cats. But Saul Kripke and Hilary Putnam have given plausible accounts of how this is possible. Imagine someone who wanted to introduce a name for a biogical kind nobody had named before. It might be someone who sees member of an exotic new species of animal. She could point to some members of that species and say something like, 'let's call that animal and every other animal of the same species a...

For any given term or concept, is it possible to formulate a correct definition? Some people claim all definitions are equally valid and subjective. I can't believe this though because if we can't agree on a definition, then you can't transmit your exact meaning to me through words, and the whole idea of communication is shot. How can definitions be rooted in reality and truth?

Take the concept of apples. There is no cosmic connection between that concept and the term 'apple'. It's just a convention, and indeed it's only a convention for those who speak English. Among English speakers, however, it does seem important for the sake of communication that we are following the same convention. Otherwise when you ask me for an apple I might give you a hamster. There is however a deep philosophical worry about how it is possible for you to entertain a concept. The issue here is not how you know that other people's concepts are the same as yours, but how you can have any general concept at all. Take the concept of apple again. How do you manage to think, not just of this or that apple you may have seen, but of the set of all apples, the great majority of members of which you will never encounter? The trouble is that the apples you have seen are not just a subset of the set of apples, but also a subset of innumerably many other sets, such as the set consisting of apples...

I'm interested in such statements as "Life is strange", "The world is an amazing place", etc. How meaningful are they when we don't have other examples of "life" or "world" to compare them with? If they are not meaningful (and I don't know whether you will conclude that they are) why do people have a propensity for making such statements?

Even if in order to find something strange or amazing you need something familiar or mundane to compare it with, we could make sense of your statements in terms of the variety within a single life or a single world. It would be something like the sentiment that no matter how much you have experienced, you are in for more surprises. So even though some things become familiar and mundane, there will always be new things strange and amazing. And maybe we can even have strangeness without familiarity, the amazing without the mundane. Could there be a life where everything is strange and a world where everything is amazing? I don't at the moment see why not.

What do philosophers mean by the term 'mental content'? My initial reaction to the phrase was to take it to mean something like 'the meaning of a thought, belief, etc.' But this interpretation seems...unexplanatory. It seems to me that things don't just MEAN; rather they mean TO some individual/group. (X doesn't just mean Y; X means Y to Z.) For any given thought/belief/whatever (X), we could imagine infinite different Zs, and through these Zs, infinite different Ys. Which Zs are the relevant ones? Why is whatever distinction is drawn between relevant and irrelevant Zs drawn as it is? Or is my vague conception of mental content as the meaning of a thought, belief, etc. not in line with how philosophers use the term? If so...what do they mean by it?

Carrying on from Joseph's answer, part of your question is whether content is relative to the person entertaining that content. One sense in which this is right concerns representations involving ingredients like 'I', 'here', or 'now'. These so-called indexical terms have the interesting feature that what they refer to depends on who is thinking them. So we could both entertain the content 'I am an avid squash player': when I entertain this thought it is about me and when you entertain the thought it is about you (and maybe it is true when I think it and false when you think it). So that is one way in which what a thought or a thought's content is about can depend on who is thinking it.

Why are philosophers these days so concerned with fleshing out possible rules for concepts (e.g., Crispin Wright's analysis of intentions)? Do they believe that people actually follow these rules? But how can that be if most (if not all) people can't even say what these rules are precisely? And wouldn't a more plausible answer be found in our being conditioned to behave in certain (imprecise) manners with certain words or phrases, much like, e.g., learning to use our legs to walk? If so, shouldn't this be more a matter of empirical investigation (on the level of science) than this sort of conceptual analysis?

I'm with Mitch: we could be using rules but they are unconscious so we have trouble identifying them. But it may also be that we don't do it with rules. Thus Thomas Kuhn in his important book The Structure of Scientific Revolutions argued that although scientific research often seems to run as if it was governed by rules, in fact the mechanism is different: scientists have exemplars. (This is the central notion covered by his notorious umbrella term 'paradigm'.) Exemplars are concrete problem solutions in the scientists' speciality, so in form they are different from rules. But they act like rules, because they create what Kuhn called 'perceived similarity relations'. Scientists choose new problems that seem similar to the exemplar problems, they try solutions that seem similar to those that worked in the exemplar, and they judge the success of new solutions by reference to the standards that the exemplar exemplifies. The exemplar mechanism is an interesting alternative to the rule mechanism as...

Can a question be a question without an answer?

I very ordinary example of a question without an answer might be a question with a false presupposition. Suppose the question is whether you have stopped beating your dog, where in fact, kind soul that you are, you never started beating your dog. In that case I think we still have a question, but although it has a good reply, it has no answer.

I am a postgraduate linguistics student engaged in a programme of research in which much of the theoretical apparatus proposed by the majority of language scientists ("Words and Rules" - à la Pinker) is dismissed as epiphenomena of exemplar-based cultural learning. Lately, however, I have been struggling with the definition of the word "epiphenomenon". Any thoughts?

An epiphenomenon is something that is real and has a cause, but does not in turn go on to cause other things. A common simile is that it is like the smoke coming out of the locomotive. Thus in the philosophy of mind epiphenomenalism is the view that experiences are caused by physical states of the brain, but do not in turn cause anything: they are just the smoke the brain gives off while it is working.