This was first published in 2002 on Pathways in Philosophy (link now dead) and then on my old site probably in 2005. One “answers” the question by dissolving it.* I republish my dissolution without prejudice to the view that doing so has little (if anything) to do with philosophizing after Christ, apart from Whom it makes no sense to essay an answer to this question or any other. For those in a hurry: “something” stands in for “everything.” The answer to “Why?,” the explanans, must lie outside everything, the explanandum. But there is nothing apart from everything. The universe could be otherwise than the way it is and therefore need not be at all: one may sensibly ask why it exists one way rather than another. Pre-creation, however, God eternally is all there eternally is. Nothing answers to the question, “Why is God the way He is?” There being nothing contingent about Him, one could never sensibly ask “Why does God exist?”
The word “something” needs clarification. We ordinarily use “something” to refer to an unidentified particular in a general way (e.g., “I just heard something; what was that?”). The question, “Why is there something rather than nothing?,” however, seems to ask in a general way about the totality of things.
The grammatical form of a question can be misleading. “Why is there something rather than nothing?” is grammatically similar to “Why is there salt in the soup rather than pepper?” or “Why are there swallows in Capistrano rather than bald eagles?,” but they are logically quite different from our question. The other questions can be answered by investigating other parts of the world (culinary practice and the nature of certain birds, respectively). The explanation in each case lies outside the thing to be explained. But the question, “Why is there everything [‘something’] rather than nothing at all?,” logically does not permit any such investigation. There is nothing “outside” everything that could yield an explanation.
In The Mystery of Existence, Milton K. Munitz argues that, unlike “Why is there something rather than nothing?,” the question “Why does the observed world exist?” is well-framed, but unanswerable. (A genuine mystery, according to Munitz, is a question that can be neither dismissed nor answered.) He rejects the theistic answer, i.e., the observed world exists because God created it, but that rejection does not affect what we have said above. The mystery of existence is neutral with respect to theism. Whether or not God exists, there is nothing outside the totality of existing things (including or excluding a God) and therefore nothing that can yield an explanation for its existence. That is, whether the totality equals “just the observed world” or “God plus the observed world,” there is—there can be—nothing outside that totality which explains it. Even when, according to theism, God was all that existed, there was no explanation for that fact, for there were no other facts than his existence to which possible explanatory appeal could be made.
As Paul Edwards put it in his (also highly recommended) essay, “Why?,” in The Encyclopedia of Philosophy:
. . . the word ‘why’ loses its meaning when it becomes logically impossible to go beyond what one is trying to explain. This is a matter on which there need not be any disagreement between atheists and theists or between rationalists and empiricists.
* Partly in response, William F. Vallicella blogged “Two Forms of the Ultimate Explanation-Seeking Why-Question”