That's a lot of difficult questions! First: I think we can do wrong to people who don't yet exist. It seems unfair to be less respectful of someone who will be born in, say, 2020 than someone who was born in, say, 1995. Second: it is not obvious that your second question makes much sense. You can't do wrong to a being who doesn't exist, never has existed and never will exist, simply because there are no such beings! A future being isn't yet around to be harmed, but will be later. But non-existent beings aren't there to be harmed.

You go on to consider a conditional: 'if ... it isn't wrong to cause them never to exist ...' where 'them' is supposed to refer to future people. But if we cause there to be no future people then 'them' doesn't refer and there is no issue about harming them.

Still one might want to argue that we have a duty not to make the planet uninhabitable because we have a duty to our species. I am not sure how to justify that, but the thought seems to have some intuitive appeal.

We need to distinguish between a posteriori and a priori arguments. Empirical sciences such as physics, chemistry and biology are predominantly supported by a posteriori evidence, grounded in experience. By contrast, the 'exact sciences' like mathematics are predominantly supported by a priori demonstration, grounded in the pure intuitions of the intellect alone. Mathematics cannot be based on experience, it might be said, because experience can only ever reveal contingent truths, whereas mathematical speculation gives us an insight into necessity. But both a priori and a posteriori knowledge can jointly be distinguished from faith, which for present purposes we might as well just define as any other basis for belief that cannot be fitted into either of these categories (e.g. the authority of a respected individual or of a text regarded as sacred, or a private inspiration supposedly delivered only to the elect).

Now, there have been many philosophers and theologians over the centuries, and still today, who have felt that, a few 'mysteries' aside, the central core of religious doctrine does not actually depend purely on faith after all, but can in fact be justified either a posteriori or a priori or both. The Intelligent Design argument, for instance, is an example of an a posteriori argument for the existence of a certain kind of creator. The Ontological Argument is an example of an a priori proof of the existence of a perfect being. But there have also been many who have felt that these arguments are fundamentally fallacious, and that ultimately the religious believer does have to fall back on faith after all. (I suppose this would be Dawkins' position -- but it's worth appreciating that many devout believers have criticised one or other of these arguments too).

Now, as for metaphysics, it seems reasonable to suggest that its necessary principles cannot be established a posteriori, in the way that the contingent laws of physics can be. I would just note in passing that, since the work of people like Saul Kripke around 1970, the notion of an a posteriori necessity has become considerably more respectable -- but even Kripke, I think, would accept that such a posteriori necessities cannot be extended to encompass the whole of metaphysics. But, if we do accept that metaphysics cannot be (fully) established a posteriori, does this mean that it must all be just a matter of faith? Not at all, for it might yet be possible to for us establish it a priori, by a method analogous to mathematical reasoning. Indeed, I take it that most metaphysicians would say that this is precisely what they are engaged in doing. They seek to show that some claim about universals (or whatever) must be true, not because of any empirical evidence but rather because all of the alternative hypotheses can be logically shown to lead to formal contradictions.

With these distinctions in place, there are plenty of combinations on the table. (i) One might believe that both a priori and a posteriori arguments are available in religion, bolstered by supplementary doctrines justified by faith, and that a priori arguments (at least) are available in metaphysics. Descartes would be a good example of this position. Or (ii) one might believe that a priori metaphysics is perfectly respectable, but have some misgivings about the possibility of one or other approach to religious knowledge. Several philosophers would fit into this category, depending on how one spells out the details. But note that the basis for thus distinguishing between metaphysics and religion probably would not depend on the natures of their respective subject-matters, so much as on the details of the specific arguments that have historically been proposed in the two domains. One can quite consistently maintain that, although there's nothing incoherent about the notion of proving the existence of God a priori, any more than there's anything incoherent about proving the existence of any other metaphysical entity a priori, the Ontological Argument is nevertheless just a bad argument. Or (iii) one might dismiss both a priori and a posteriori knowledge of religious doctrine, and also dismiss a priori metaphysics. The classic example here would be Hume, who was happy with a priori reasoning in mathematics and with a posteriori reasoning in empirical science, but who rejected everything else. As he famously put it, in the closing words of his Enquiry concerning Human Understanding:

"When we run over libraries, persuaded of these principles, what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion."

I'd like to take this question in a slightly different direction. I accept the point made by Prof. George: we don't need to think of the phrase "absolutely nothing" as referring to something; the logic of "There's milk in the fridge" isn't the same as the logic of "There's absolutely nothing in the fridge." But I'd like to pick up on a point in my colleague Prof. Levinson's reply: that if there being absolutely nothing is a possible state of affairs, then reality contains that possibility.

Start by mulling over the idea that there being absolutely nothing is a possible state of affairs. A person might wonder: is a state of affairs something? Are there such things as states of affairs? How about possible states of affairs? If so, then so long as there is at least one possible states of affairs, there's not absolutely nothing. Now suppose -- as at least some philosophers seem to -- that for it to be possible that X, there must be a possible state of affairs in which X is true. This brings us to a conundrum. Suppose we think: there could have been absolutely nothing. On the line we've been following, that means that there must be a possible state of affairs in which it's true that there's absolutely nothing. But if there is, then there's at least one thing: that possible state of affairs. And so the supposed possibility that there might have been absolutely nothing turns out to be incoherent after all.

Anyone who's bothered to read this far might be wondering: was writing all that a good use of a grown man's time? But perhaps we can use it to point to a slightly less seedy line of inquiry. Philosophers have sometimes thought of existing things as falling into one of two categories: contingently existing or necessarily existing. The stuff around us -- my computer, me, you, the Empire State Building... are in the first category. But is there anything in the second? If there is, then for reasons that don't call on my sleazy paradox, it's not possible that there might have been nothing. Some things -- the necessary ones -- exist no matter what.

What might count? The Ontological Argument claimed that God is a necessary being. It's a fascinating argument, but for my own part, I don't think it works. But some abstract entities might fit into the category of necessary beings. One interesting candidate, amusingly enough, is the empty set: the set with no members at all, denoted as Ø. If there's really such a thing as the empty set, it's hard to see how it might have failed to exist. So perhaps it's a necessary entity. And if it is, it brings an infinity in its wake: we get the set whose only member is the empty set, usually written {Ø}, the set whose members are Ø and {Ø}, written {Ø,{Ø}}, and a dizzying infinity beyond that.

Not everyone agrees, needless to say. But maybe, just maybe, the empty set is the ultimate stopgap against existential emptiness.

Assuming that in some sense no statement can be true unless it corresponds to reality or to how things are, which is not that bad a principle, the possibly true statement in question, note, is not, say, that absolutely nothing exists (which, as the other respondent suggests, has a tricky logical grammar), but most likely, that there being absolutely nothing is possible, or a possible state of affairs. Well, that might indeed be true, but then it does also correspond to reality, in the sense that reality, as we understand it, indeed contains or admits of that possibility.

Even if you are right that each of the options you describe is difficult to accept, I'm wondering how you can possibly treat "this whole existence thing" as a hallucination or a complete joke? Are you saying that you don't take the question seriously (but do take your and others' existence seriously), or are you saying that you don't take existence seriously?

If your point is that you don't think it is worth continuing to ask the question, I can sympathize; but I would suggest that you may want to think a bit more about (a) whether there are presuppositions that are responsible for the seeming incoherence of each option, and if so what they are, and (b) whether there are questionable presuppositions of the question. I note, in fact, that you don't actually forumate a question, even though you are considering possible answers. What, exactly, is the question you are seeking an answer to? Is it "Why is there something rather than nothing?" Or "What is the cause of everything, i.e., the whole shebang?" Or... Note that there may be very different strategies than the ones you mention for addressing these different framings of the issue.

If your point is that because the question you're asking has no answers, existence is a joke or hallucination, then this is a very bold conclusion, given that the fact that you exist is hard to even question (by you) coherently. And even if we can't be sure how the whole shebang came into existence or why, that uncertainty doesn't call into question that it does exist. Does it?

I know exactly what you mean. The question seems alternatively irresistible, frustrating, intoxicating, and ridiculous. I suspect that the early modern philosopher Immanuel Kant maybe right that the very attempt to reason out an answer draws us into an irresolvable mess, that at the end of the day we can't figure it out. There a couple of bits I'd observe about the way you pose the question, however.

First, there may be more alternatives than you think. You may mean by (2) that the universe sprang out of nothing (as philosophers like to say, ex nihilo) or just appeared, but it needn't therefore have been created. The Big Bang theory runs somewhat along these lines. But the Big Bang theory is also consistent with the idea that the universe sprang forth from something besides God or nothingness, something unknown to us. Would it also make sense to say that there may be other ways that time could be organized to make the sort of linear past-present-future model your question depends upon not really meaningful for the universe as a whole?

Secondly, keep in mind that in an important sense, it's not meaningful to speak of anything "before" the beginnng of the universer because time seems to have begun with the universe, to be an aspect of the universe and the motion/change of its consitutents. Also truly weird, I know. Technically, there was no time before the Big Bang, at least not time as we know it.

Thirdly, is it really incomprehensible that the the universe has always existed? Many have found this idea perfectly comprehensible. I don't really kow myself, but one tantalizing challenge to the idea that the past is infinitely long is this: if the past were infinitely long, then an infinite amount of time would have had to have passed to reach the present moment--and that is impossible, because an infinite amount of time cannot be completed.

If someone asks me what's in the refrigerator and I answer "Absolutely nothing", what am I saying? I'm not saying that there's something in the refrigerator after all, namely absolutely-nothing. What I'm doing is denying that there is something in the refrigerator. Although the sentences "The milk is in the refrigerator" and "Absolutely nothing is in the refrigerator" are grammatically comparable, their logical structures are different. In order for the first claim to be true, there must be something that "The milk" refers to and that something needs to be in the refrigerator. But that's not the case for the second claim. In order for the second to be true, the claim that there is at least one thing in the refrigerator needs to be false. It is not the case that in order for the second to be true "Absolutely nothing" must refer to something and that something is in the refrigerator.

People have, for thousands of years, been misled by the superficial grammatical similarities of these two claims and have, for as long, been battling the philosophical conundrums (of the kind you formulate) that this false assimilation leads to. Complete clarity about all this was only achieved towards the end of the 19th Century, in large part due to the work of the German mathematician-philosopher Gottlob Frege. For a related issue, see Question 49.

Your question suggests that answers to the question “What is the function of X?’ will have normative implications about what we ought or ought not, may or may not, do to Xs. And this fact is puzzling. How, you might be wondering, can certain facts about an object’s function have any implications about what I may or may not do to it? And I think that you are right to be skeptical: in the case of ashtrays, functional definitions have no normative implications for us– about what we may or may not do to them.

However, behind your question may be Aristotle’s “function argument” in the Nicomachean Ethics (I 7), where he argues that information about the “function” (ergon) of humans has implications for what sort of life humans ought to live-- “ought”, that is, if they are going to be well off.

On my view, Aristotle’s notion of function does not correspond to any of the three notions of function that Nick distinguishes for ashtrays. To distinguish Aristotle’s notion from those that Nick defines, I’ll refer to it as an object’s “real function.” On Aristotle’s view, the notion of an object’s real function plays a significant explanatory function. If I want to know why this hammer has the attributes that it has, I have to understand what the hammer is for. If I want to know why hearts have the attributes they have, I have to know what they are for. Hammers and hearts can be used for all sorts of purposes, but not all of these purposes will be equally useful for such explanatory purposes.

The fact that we put objects to uses other than what they are really for usually doesn’t much matter– sometimes we can put objects to better use than we could if we restricted ourselves to using them only for real function. This statue is quite hideous, but it makes for a very effective doorstop. On Aristotle’s view, there is a significant exception to this general rule. While we might put other objects to better use than what they are really for, our own selves are a different matter altogether. On Aristotle’s view, if we are going to live the best life, we must perform our real function and do so well.

You're right to suspect that the idea of function is somewhat unclear--at least in most uses. In one sense, a thing may be said to "perform a function" just in case it does whatever it is that is within the description of the function. So, a highball glass can "perform the function" of an ashtray, because it can do what we ordinarily associate with the ashtray--that is, serve as a receptacle for ashes.

Something made to be an ashtray would be an object for which serving as a receptacle for ashes would be its "intended function." The intended function of a highball glass (whose intended function was to be a drink container of a certain size and shape) is not to be a receptacle of ashes. So the object whose intended function was X may end up performing some other function.

Now one way in which things can shift functions is because beings capable of forming intentions can decide to change the functions the objects serve, either temporarily or permanently. So we can turn an old tire into a swing, or a highball glass into an ash tray.

Now, a function is not necessarily to be understood in terms of purposes, but may sometimes be best understood in terms of what the thing customarily or ordinarily does, as a matter of fact, or as a matter of the sort of thing it is (call this a "natural function". In this sense of function, a thermostat is "functioning" if it senses temperature and opens and closes a circuit at the appropriate times as a result. Doing this may be the "purpose" of the thermostat (from the point of view of its maker, or user), but it could continue to perform this function even if all sentient life were to disappear, so that it would no longer serve any purpose.

So, an ashtray could be: whatever happens to be used as a receptacle for ashes (performed function), whatever was made to be one (intended function), whatever beings with intentions take to be one (showing their purpose for the object), or whatever normally and customarily serves as one (natural function).

We use language to draw distinctions of various kinds. Some such distinctions are binary -- such as that between prime and nonprime natural numbers or that between pregnant and nonpregnant female persons and animals. Other such distinctions are scalar -- such as that between objects called long or short, fast or slow, North or South, suggesting a scale along which things can be ordered. Yet other such distinctions are plural -- such as the distinctions we draw by means of color predicates.

As your example brings out, distinctions of different kinds can sometimes be applied within the same space. In the space of colors, for instance, we might operate with a simple binary distinction (blue/nonblue) or with a scalar distinction (bright/dark) or with a plural distinction (mauve/crimson/turquois/...). Similarly, in regard to CD collections, we might operate with a simple binary distinction (unique/nonunique) or with a more complex scalar or plural distinction.

Which kind of distinction we employ typically depends on the purpose at hand. A guy locked out of his apartment may want to distinguish among keys in a simple binary way according to whether they do or do not fit his door. An avid key collector, by contrast, may draw much more complex distinctions among keys.

The air of paradox in your example arises from the fact that you place a word -- "unique" -- used to mark a binary distinction into a context in which a more complex distinction would seem more appropriate. When assessing a CD collection as indicative of her owners taste, we are typically not simply interested in whether her collection does or does not match someone else's precisely. As you suggest, we are usually interested also in the degree of overlap between her collection and its closest match -- as well as (I would add) in how her collection compares to yet further collections.

This being so, we can nonetheless avoid your paradoxical (or revisionist) talk of CD collections being more or less unique. We can instead make the point in different language, with a word like "distinctive," for example. A CD collection is the less distinctive the more overlap there is with its closest match and the more overlap there is with other CD collections more generally.