atheist: a person who denies or disbelieves the existence of a supreme being or beings [dictionary.com]The first definition defines an atheist as someone who maintains that gods do not exist. The second defines an atheist as someone who is not a theist.
atheist: a person who does not believe in the existence of God or gods [Oxford Dictionaries]
The distinction is relatively unimportant in everyday usage since most of us who are nontheists will argue that gods do not exist. But when you're arguing with a philosopher you need to pick nits since philosophical arguments often turn on definitions. No intelligent atheist wants to be trapped into arguing that gods do not exist since that's like trying to "prove the negative" and we all know that it is impossible to prove the nonexistence of something.
There's a class of philosophers (professional and amateur) who prefer to be called agnostics. As a general rule, those philosophers use the restrictive definition of atheist and that's why they deny that they are atheists. They do not seem to be sympathetic to any other definition of atheist since that might require them to admit they are atheists, as well as agnostics.
I encountered one of those types in the comments section of Trying to Understand Agnostics. Joe Agnostic wrote ...
Larry Moran wrote:
Is it your position that I'm guilty of "intellectual bankruptcy" by proposing a definition that better reflects my position and that of many other atheists?
I am saying that you are either engaging in creative humpty dumptyism or displaying a severe lack of intellectual curiosity in failing to realize that there are perfectly good words which already exist that might better capture your position, such as theological noncognitivism or simply nontheist.
How would you react to one of your students trying to redefine the meaning of exothermic - or redefining natural selection to incorporate orthogenesis? I hope you can see how silly that is.
Your infatuation with the term Atheist is blinding you to its actual meaning - and your blind desire to redefine that meaning is undermining any claim to an intellectual high ground.
Ergo, the only intellectually valid position is agnosticism. Nobody can be an agnostic atheist because agnosticism and atheism are incompatible by (his) definition.1
Joe insists that modern atheists are trying to change the meaning of a commonly accepted definition. (I don't know if that's the position of John Wilkins.) I don't know enough about the history of the word to know if Joe is correct, although the article on atheism in Wikipedia suggest that both meanings are quite old.
However, regardless of historical precedence, it is perfectly okay to promote a definition that reflects modern thought on the topic. We do this all the time in science—the redefinition of "evolution" and the refinement of terms like "natural selection" are perfect examples.
I suspect that the resistance we encounter from agnostics has more to do with their reluctance to become associated with a word that has negative consequences in some societies than with any real intellectual high ground. If I were being mean (heaven forbid!) I'd even say that Joe is the one who's a bit blind.
Let's close with an example of a famous theist who tries to teach atheists the "proper" definition of atheism. He seems a bit frustrated because his opponent won't jump into his trap.
To me this sounds just as silly as Joe Agnostic.
1. It's interesting that these hard-core agnostics are far more likely to criticize the position of atheists than theists.