Just what do we mean when we say “atheist,” or “agnostic”? It’s a subject that can cause quite a bit of confusion, even among those who define themselves as one or the other.
By far the most common shorthand definition of “atheist” is “someone who doesn’t believe in God.” Many atheists have a problem with that definition, not least because it’s framed within a religious, monotheist viewpoint. It implies, sort of, that God actually exists but that atheists are people who don’t realize that.
Not to mention, it assumes that theism equals monotheism, and fails to take into account the various other theistic views (e.g. Hinduism with its millions of deities). Personally, I don’t think this is a huge problem. If you don’t object to saying you don’t believe in Santa Claus, I don’t see why it’s any different (when living in a culture where Santa Claus and God are both commonly understood concepts of supernatural beings) to say you don’t believe in God.
A bigger problem with “doesn’t believe in God” is that it’s grammatically imprecise. It’s like saying “I don’t like kumquats” — it could mean you’ve tried them and dislike them, or that you’ve tried them and have no particular like or dislike, or that you’ve never tried them at all, and therefore have no reason to say you like them.
Of course, when someone in casual conversation says “I don’t like kumquats,” the sensible conclusion is that they’re tried them and they dislike them, but that’s not quite the same with “I don’t believe in God.” A person who says that may mean that they believe God doesn’t exist (and most likely they don’t believe in any other deities either), or that they neither believe that there are deities nor actively believe that there aren’t any.
Some people define “atheist” literally as “a-theist,” someone who merely isn’t a theist. Generally, they define a “strong atheist” as someone who makes the affirmative assertion that there are no deities, and a “weak atheist” as someone who simply lacks any belief strong enough to make an affirmative assertion either way.
In this view, “agnostic” refers to the belief that the deity question is unknowable and unanswerable. I find that unsatisfactory, for a number of reasons, not least of which is that any sensible person — theist or atheist — considers the deity question unknowable. That doesn’t mean we can’t have an opinion on the subject, it just means that any sensible person — atheist or theist — should acknowledge that their opinion or belief is just that. It’s not certainty or knowledge.
When someone says “an atheist is someone who doesn’t believe in God, and an agnostic is someone who doesn’t know,” my immediate response is to say that therefore everybody’s an agnostic, since nobody knows.
I prefer to use the word “atheist” to mean someone who believes that there aren’t any deities, and “agnostic” to mean someone who doesn’t believe either that there are or aren’t any.
What about “freethinker”? To me, that’s best used as an umbrella description for atheists and agnostics (by whatever definition you use), those people whose worldviews don’t include a belief in any deities. I also tend to think it’s a term best used en famille, with other like-minded folks, rather than in discussions with religious people, since it’s kind of a self-compliment, implying that other people’s thinking isn’t free. That may in fact be true, but it’s not polite to mention with company around.
(Agnostic cemetery cartoon by Dan Piraro)