Atheist versus agnostic: these words are often seen as opposing sides of a dichotomy. If you're not a religious believer, you're either an agnostic who's just not sure or you're an atheist who's absolutely certain of the non-existence of god or gods. The commonly assumed definitions of these terms, though, are incomplete and, especially in the case of atheism, not really very useful. Even non-believers such as Albert Einstein and Carl Sagan rejected the "atheist" label because, to them, it implied certainty.
Einstein, for instance, insisted he was not an atheist even while writing,
|It was, of course, a lie what you read about my religious convictions, a lie which is being systematically repeated. I do not believe in a personal God and I have never denied this but have expressed it clearly. If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it.|
|An atheist has to know a lot more than I know. An atheist is someone who knows there is no god.|
but also wrote the seemingly conflicting:
|Life is but a momentary glimpse of the wonder of this astonishing universe, and it is sad to see so many dreaming it away on spiritual fantasy.|
Both men made it clear they were non-atheists who held no beliefs in a personal god. Were they atheists, or agnostics... or both? Neither?
Agnosticism: I Don't Know
Credit: Zazzle.comThe term "agnostic" is believed to have been coined by TH Huxley around 1873 from the Greek a- ("not") and gnostos ("to be known").  So an agnostic is simply a person who does not claim to know whether the divine exists or not. Some take it further, claiming that it is impossible to know.
What's important to note is that agnosticism only describes one's claimed knowledge of God and says absolutely nothing about one's belief. It's very likely that church pews all over the world hold a vast number of doubting believers, and likewise that many readers with a copy of "The God Delusion" on their bookshelves don't claim to know for sure if God is real.
Atheism: I Don't Believe
Credit: releasingreligion.blogspot.comAtheism, also from the Greek, means literally something like "no god belief" - and the key word here is "belief". Atheism is, in general, not a belief in the lack of gods, it is a lack of belief in gods; the distinction is subtle but important.
Exceedingly few people, even among the most vocal and vehement promoters of non-belief, will ever claim or have ever claimed to "know" that the supernatural doesn't exist. Instead, almost everyone will agree that it's not logically possible to disprove anything - not God, not Allah, not Zeus, not Odin, and not the invisible robot that's filming you for a popular extra-dimensional reality show as you read this. The real atheist position, for most, is simply that none of the claims made about the divine are backed up by sufficient evidence to accept them as reality. The statement, "I don't believe and there's nothing you can do to change my mind" is uncommon and looked down on within the atheist community; for them, a more appropriate response to religious claims would be, "Really? Why should I believe that?"
Carl Sagan said, "Extraordinary claims require extraordinary evidence", and Christopher Hitchens took it a little further by stating, "That which can be asserted without evidence, can be dismissed without evidence.". This is the driving philosophy behind most expressions of non-belief. Even Richard Dawkins, perhaps the best known proponent of the co-called "New Atheist" movement, proposes in his book "The God Delusion" a seven-point scale of belief, where "1" is absolute surety about the existence of god(s), and "7" is absolute certainty that they don't exist. He then rates himself as a "6" to "6.9" on that scale.
The Agnostic Atheist
While it's difficult to obtain hard data to know for sure, it seems likely that most self-proclaimed atheists are also agnostics and most self-proclaimed agnostics are also atheists. The agnostic atheist is the person who says "I don't or can't know, but my experience so far has not led me to belief." There's room in this spectrum for a wide range of opinions on religious practices and positions.
It's even possible and, I suspect, not uncommon, to be an agnostic theist: "I can't be sure, but I believe anyway."