So, agnosticism - fence sitting, stealth atheism, weak atheism, non position, and so forth. As mentioned previously - and rather long ago - there are many different definitions of agnosticism, as there is of atheism, making explanations referring to atheism frequently recursive or problematic. The Religious Tolerance page on the subject delightfully and perhaps unwittingly elaborates just how tremendously unhelpful such dilution and broadening of the concept has been.
The term was coined sometime before 1869 by none of ther than T.H. Huxley - Charles Darwin's 'bulldog'; defender of evolution from the dark, whiffy forces of antiknowledge, and one of the first people to outright argue one of the most entertainingly offensive corollaries of common descent - that humans were themselves descendents of ape-like organisms. Brilliant, anticipatory, loving, compassionate - he is raved about here, and I command you to go, go, to better give the lad mad props, what.
Huxley had a rather vituperous and long-lived disdain for dogma of all varieties, but he was careful to avoid charges of being an infidel publicly and to present his views in a frequently sympathetic light - while in letters, and with not a bit of humour, revelled in the fools he was making out of numerous opponents. At the same time his wit and his defenses were frequently barbed and extensively devastating. Dear Huxley was a real life troll.
Privately he acknowledged he was technically an atheist - he did not believe in a personal, interested God, rejecting the idea thoroughly - whilst still having a problem with the atheism of the day:
I have never had the least sympathy with the a priori reasons against orthodoxy, and I have by nature and disposition the greatest possible antipathy to all the atheistic and infidel school.
Such disdain was in part due to the importance Huxley placed on methodology over faith: that is to say, how one comes to his conclusions was of utmost importance to Huxley, seemingly to a much greater extent than the actual positions that man held; unthinking, close-minded doctrine was bigotry in the hands of the atheist as much as in the hands of the theist. He wrote repeatedly against the doctrine of philisophical materialism on such grounds, and extended the argument to suggest that science and religion were complementary:
The great deeds of philosophers have been less the fruit of their intellect, than of the direction of that intellect by an eminently religious tone of mind. Truth has yielded herself rather to their patience, their love, their single-heartedness, and their self-denial, than to their logical acumen.
And all the reformations in religion–all the steps by which the creeds you hold have been brought to that comparative purity and truth in which you justly glory–have been due essentially to the growth of the scientific spirit, to the ever-increasing confidence of the intellect in itself–and its incessantly repeated refusals to bow down blindly to what it had discovered to be mere idols, any more.
It is above all things needful for you, working men, to note these truths. For with the limited time, and the limited means for study at your disposal, you run the risk of flying to one of two extremes–bigoted orthodoxy, or conceited scepticism.
These ideas are expanded and frequently returned to in subsequent essays and speeches, as Huxley developed an argument not entirely unlike Gould's 'nonoverlapping magisteria': science was pre-eminent at unravelling the mysteries of the natural world, while religion was relegated to ethical matters, matters distinct from 'the intellect'. He argued that when religion - specifically, theology - abandoned science in its understanding of the world it became false, bizarre and irrational. The spirit, the self-discipline and the values of religion guide, drive and enthuse the skeptic, but the scientific method best reveals the world around us, was the most honest and useful system by which personal belief should be developed. His arguments against antiscientific dogma are already quite stringent, and he notes that while 'no honest man can, for one moment, reconcile the plain teachings of geology with the statements contained in the book of Genesis' he warns against the desire to 'treat with foolish ridicule the book which the true man of science will ever hold in the highest respect, as containing the noblest and the clearest exposition of human rights and human duties extant.' All somewhat Thomas Jefferson.And I'm rather in disagreement with the idea that the Bible is a particularly moral book (see, for instance, these joys); his understanding of what he terms 'religion' is also left somewhat ambiguous - one suspects with some intention, as he was an extremely savvy fellow; his essays and speeches also established his recognition of the scientific value of automatism - the notion that man and beast was best viewed as biological and intricate but ultimately mechanical and understandable structures, contributing strongly to the methodological naturalism which Darwin and Lyell had set in motion. Nonetheless, the immense value he placed in the Bible for its morality was consistently held throughout his life.
Huxley believed himself ignorant about purpose in the universe, he was questioning about the nature and purpose of man, the nature of God, the reality of miracles and other, wide ranging potential phenomena, and 'agnosticism' described the state his own lack of rigorously derived knowledge and understanding of such matters. His understanding of what agnosticism meant is somewhat stricter than it is popularly understood today:
Agnosticism, in fact, is not a creed, but a method, the essence of which lies in the rigorous application of a single principle. That principle is of great antiquity; it is as old as Socrates; as old as the writer who said, "Try all things, hold fast by that which is good" it is the foundation of the Reformation, which simply illustrated the axiom that every man should be able to give a reason for the faith that is in him; it is the great principle of Descartes; it is the fundamental axiom of modern science. Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable. That I take to be the agnostic faith, which if a man keep whole and undefiled, he shall not be ashamed to look the universe in the face, whatever the future may have in store for him. -Source
The modern idea of agnostic theists or agnostic atheists was quite alien to Huxley's conceptualisation: he stated flatly that 'Agnosticism [...] simply means that a man shall not say he knows or believes that which he has no scientific grounds for professing to know or believe.' Which leaves us with a bit of an issue - popularly, ' agnostic' is regarded as the idea that God is unknown or unknowable; that this is the central tenet, as revealed in descriptivist dictionaries (The American Heritage Dictionary, for instance, would rule out Huxley himself from being agnostic). And yet the idea that unproven, faith-based belief of all varieties is to be rejected is far more critical to Huxley. While he rejected dogmatic skepticism he propounded an accurate, honest and perhaps the most definitively skeptical methodology of all.
It was the dishonesty, the authoritative presumption which he rejected in theology, which he rejected in the strong atheist, and it's somewhat bizarre for self-identifying agnostics to embrace so warmly such cognitive dissonance. While an agnostic may hold, based on their current scientific understanding, that it is unknowable - or perhaps simply unknown - whether God exists, as Bertrand Russell points out it follows that 'an agnostic does not believe in God' - theism and atheism would not be beliefs reached through reason; therefore they simply would not be agnostic. We do not know if there is a God, therefore we cannot and should not believe there is or is not one. Our beliefs and sense of ethics are best informed by what we know, by what we have strictly tested and tried to disprove, rather than what we hope or guess to be the case.
The best chops of any thinking man