I thought I'd write a brief followup, followed by a lengthy excursus, to the atheist/agnostic distinction, largely because my position has changed a bit. I think it is important to acknowledge the mutable and sometimes contradictory possible uses of any single word, and these two, politically charged as they are, are exemplary.
While there are surely as many forms of atheism as there are thinking atheists, we can usefully suppose them to fall into two broad camps: those who believe there is no god, and those who don't believe there is a god. Both camps can be described as not believing, or as being a-theistic. Agnostics too have two similar sects: those who do not know if there is a god, and those who have not decided if they think there is a god. Again, both follow from etymology: members of either camp would say they do not know, they are a-gnostic.
It follows then that there are both gnostic atheists and agnostic atheists, and that there are agnostic atheists and agnostic fence-sitters. This is what I think Mike means when he says that atheism and agnosticism are not mutually exclusive. Using this rubric, it would be accurate to say I am an atheistic agnostic--I do not believe there is a god and I do not know. For me, this non-knowledge is a structural inevitability (as is the non-belief), and I, in my more arrogant moods, occasionally go so far as to suppose that this inevitability is a result of the human condition--that is, we are all atheistic agnostics, but some of us lie to ourselves better than others. This last position is fairly weak (and often insincere) and requires something like a stable intellectual identity from which to divine a "real" belief (or lack thereof).
OK, that was the brief part. Now I'm going to irritate you a little, if you'd like.
The day after Mike posted his response, I happened upon a fun little book by Lyotard called The Differend. Here is the book's first sentence: "As distinguished from a litigation, a differend would be a case of conflict, between (at least) two parties, that cannot be equitably resolved for lack of a rule of judgment applicable to both arguments." My reasons for writing about this now are immediately apparent.
Lyotard discusses the structure of these parties in terms of modes of discourse, or phrase regimens. A given regimen dictates what can or cannot be logically said, and when different regimens come into contact, contradiction or conflict is inevitable. In such situations, if a member of one party feels she has been wronged but cannot express or support this claim in terms acceptable to the other party's phrase regimen, she becomes a victim; whatever harm done her is invisible to the party that inflicted it. Lyotard's favorite examples are holocaust deniers (who construct their phrase regimen in such a way that proof becomes impossible) and labor disputes (in which case the language of capitalism prohibits the thinking of the individual as anything but a commodity). A feminist might just as easily have talked about rape (the case of Haliburton, and other contractors who oblige employees not to sue in the event of rape, comes to mind), and in the present discussion we could talk about atheists or Christians.
Now this touches on a few things, and I fear I won't be able to address any of them adequately yet. Here are a few of them.
As far as I've made it in the book (which I'm afraid I'll have to conclude a degree or so later) there are few ways indeed to avoid the victimization that comes from a differend. One is to have an arbitrator, whom both parties agree will resolve the difference fairly. This amounts to subsuming both phrase regimens under a third. A second possibility is for both parties to act in good faith to resolve the difference (Lyotard's example is Socrates). Now the problem with both of these solutions is convincing a party with a disproportionate advantage to accept a mediator, or conversely for a weaker (but not too weak) party to refuse to act in good faith (think Republicans).
From the outset this problem is seen as insurmountable. Thus the books "problem": "Given 1) the impossibility of avoiding conflicts (the impossibility of indifference) and 2) the absence of a universal genre of discourse to regulate them (or if you prefer, the inevitable partiality of the judge): to find, if not what can legitimate judgment (the 'good' linkage), then at least how to save the honor of thinking."
Much of this, as presented here, is rather cliché; I don't mean to be revealing tremendous truths. Anyone with a little common sense will notice that schools of thought clash with one another and that resolution, especially on a large political scale, happens at the expense of someone who often cannot tell you all about it. But I am drawn tot his particular presentation for two reasons: one is the ease with which Lyotard allows us to link (in terms of power relationships) fascism, capitalism, misogyny, and certain forms of theism; the other is its deliberate distancing of ethics (which is essentially the context for the book) from humanism.
I should elaborate what I mean in the first case. We are now all to familiar with the anger and bigotry of the religion of love. Many of our more wrathful religious compatriots delightedly malign even the most well-meaning non-theists, as if the anticipation of God's vengeance were too much to bear. Still others, who hide their disgust behind a mask of liberalism, condescend to pity our empty lives, and wonder at how we can even get up in the morning, much less appreciate beauty and joy, without His Helping Hand. When in discourse with these folk, there is naught but the differend; every utterance from either party passes those of the other like so many flying Dutchmen. But it really is "every" from "either." We must take care, as I have not necessarily done here, not to act in bad faith ourselves. There are some religious phrase regimens that function fully outside of the rationalism many non-theists hold in common, and we do well to remember that this does not, in itself, delegitimate either religion or these specific phrase regimens (though it also does nothing to legitimate them). There is instead a structural dissonance between many theists and many non-theists that cannot be resolved. The battle should remain (and for many is) against an encroaching theism, one that creeps up on our schools and courthouses. (This is not written with anyone in mind, though now that it's written, it calls to mind, but does not fairly characterize, some of Hitchens' more vitriolic outbursts.)
The last point I'd like to make is in relation to humanism. Humanism remains, for many marxists and non-theists, a critical ideology, but Lyotard, amongst others (Althusser has some interesting fairly early writing on the subject, and Deleuze is where I'd send anyone looking for something far-reaching) does a good job of claiming ethics for anti-humanism. Here is a portion of the "Stakes" of his book: "To refute the prejudice anchored in the reader by centuries of humanism and of 'human sciences' that there is 'man,' that there is 'language,' that the former makes use of the latter for his own ends, and that if he does not succeed in attaining these ends, it is for want of good control over language 'by means' of a 'better' language."
Lyotard means this mainly in defense of the working class, and I draw attention to it for two reasons. One is highlight the importance of atheist agnosticism for feminism and marxism. The agnostic position is an acknowledgment of both the limits of knowledge and of discourse; there will always be something outside our experience, and we must not try to speak for it.
The other reason is almost an apologia for theism. The inability to articulate one's position, either in one's own phrase regimen or (especially) in someone else's, does not amount to a failure of mastery. Language is not a tool used by humans, it is part of what humans are (eliding questions of ontology). Some truths (and I use the word mistakenly) do not translate, and it is not incumbent upon those who submit that they have been wronged to explain to us in our terms what the wrong was.
I am getting dangerously close to a position I do not espouse. I do not mean to say that there is an oppressed religious majority in the US, or that allowance must be made for I.D. with respect to evolution. Indeed, most of what I've said is much more pertinent when the non-theist is in the position of the wronged--people don't often get fired or receive death threats for being christian, and when they do it's not from non-theists. What I mean to say is that we must take care not to become what assails us, and that Lyotard's work to move beyond humanism provides a beneficial support against this possibility.
I apologize too for any (logical or otherwise) inconstancies. I compose these things stream of consciousness, and reserve my editing for things that might end up in ink. :)