We sometimes make the mistake of thinking that statements such as "X is a Christian" and "Y is an Atheist" are similar statements. Yes, they are grammatically identical, but logically they are very different (aside from being theologically different).

The "a-" prefix in "atheism" and "atheist" is the negative prefix in Greek, and it means simply "non-," "not." Atheist means, then, "not a theist." And that is ALL it means. (A "theist" is one who has some belief in a deity or deities.)

Therefore, to say "So-and-so is an atheist" is not an affirmative statement, but a negative one. It is like saying "So-and-so does not own a Ford." Or "So-and-so does not eat peanut butter." Or "So-and-so is not a Hindu." From these negative statements it is not justifiable to draw any further conclusions about So-and-so; there is no affirmative information in those statements.

To put it another way, such a statement is not saying that so-and-so is a member of the atheist class, because there is no such class. At least, there is no such class about which any meaningful statement or generalization can be made. It is a class only definable in terms of the theist class, and thus it is not a meaningful class. That is, the only thing that atheists (non-theists) have in common is that one characteristic: non-membership in the theist class.

Hitler was not a Hindu. I am not a Hindu. Do you know anything more about me or about Hitler, from those statements? Do those statements imply any further characteristics he and I may have in common? No.

Even the characteristic of non-belief in God can take many forms. Some atheists affirmatively deny God: "There is no God, that's for sure." Others say: "I have no belief in God because the evidence I have seen so far does not, in my view, warrant such a belief." Still others say: "I don't believe in God, because if I did I would have to act differently." And others say: "I don't give a damn, one way or the other."

Since none of these people have a belief in God, they are not theists. Therefore, the term a-theist (non-theist) is appropriate for them, even though the term tells us nothing more about their beliefs, their morals, or their lives than that one bare, negative fact.

So, don't lump atheists together. Atheists are not a group. We have no common beliefs, no scriptures, nothing necessarily in common except the lack of that one belief.

To say that "Z is a Christian," however, provides us with a great deal of information: Z is a theist, a follower of Jesus and the teachings of the New Testament (however they may be interpreted). We can get a general idea of what Z believes by reading those scriptures on which the Christian religion is based (although our idea may be mistaken in some details). Z can theoretically be evaluated as to how "true" a Christian he is by how correctly he interprets his scriptures and by how closely he follows the precepts of his religion. For atheists, however, there is no such standard. It would be ridiculous to say that "X is not a very good atheist" or "Y is a true atheist."

George H. Smith, in his book Atheism, Ayn Rand, and Other Heresies, a sort of sequel (1991) to his earlier book Atheism: The Case Against God, discusses a number of different kinds or bases for atheism, (pp. 183 ff):

ETHICAL ATHEISM or EXISTENTIAL ATHEISM (Sartre, Camus):

Because life is absurd, there is no god. The idea of god is inconsistent with the idea of freedom.

PSYCHOLOGICAL ATHEISM (Feuerbach):

Ideas of god are simply of psychological origin.

SOCIOLOGICAL ATHEISM (Engels, Bakunin):

Ideas of god are false because they have caused social repression.

PRAGMATIC ATHEISM:

Ideas of god are not useful, therefore they must be false.

METAPHYSICAL ATHEISM (d'Holbach, Marx):

Since only matter exists, god - being immaterial - cannot exist.

EPISTEMOLOGICAL ATHEISM:

Knowledge of god is impossible. There are several subcategories:

SKEPTICAL ATHEISM: (based on Hume, although Hume was not atheist)

Since one cannot be certain of knowing anything, one cannot know of the existence of God.

LOGICAL-POSITIVE ATHEISM (Ayer):

Any statement about a transcendent being is fundamentally meaningless.

LINGUISTIC-ANALYSIS ATHEISM:

Since the term "god" cannot be defined, it cannot have meaning.

OBJECTIVIST ATHEISM (Ayn Rand):

Proof of anything about god has never been satisfactorily given.

"Agnostic" is a term often used for those who say that they "don't know" whether there is a god or gods. The root of this word is the Greek word "gnosis" meaning "knowledge." Thus, this term is also a negative: an agnostic is a "non-knower." Agnostics, then, are a particular kind of atheist, since they also are not theists; i.e., they lack a belief in God. It has become customary for open-minded atheists to call themselves agnostics, to distinguish themselves from those atheists who affirmatively assert the non-existence of god, but I personally don't find the distinction useful or accurate... (isn't everybody open-minded?).

Just for interest's sake, not to prove any point whatsoever, here are some figures from the 1996 World Almanac about the world's religious beliefs: