I've seen many atheists try to distance themselves from the concept of 'belief'. They will tend to argue that atheism isn't a belief, but rather the lack of belief. They will say that an atheist doesn't believe that there is no god, but rather lacks any belief that there is one. They will point to the infinite possible things that may or may not exist, and say that you don't explicitly believe that these things do not exist, but rather that you don't hold a belief unless there is evidence to support it.
I understand why many atheists head down this path of reasoning. It's a common debating tactic of religious people to claim that atheism is 'just another religion' or 'just another belief', implicitly or explicitly trying to remove any claim atheism has to being more truthful or rational than all the religious belief systems.
Now it's certainly true that atheism isn't a religion. However you want to define a religion, it really doesn't seem that atheism will fit the bill, since it's purely the belief that there is no god. There are no other core 'tenets' to atheism. While many atheists will tend towards similar moral principles and beliefs (such as humanism), these are not part of atheism itself, just like most atheists accept that evolution is true, but evolution is not a tenet of atheism.
The problem I have is with atheists trying to distance themselves from the concept of 'belief'. I'm yet to meet an atheist who doesn't actually hold the belief that there is no god, whether they consciously realize that they hold this belief or not, and here I hope to explain why this is the case.
Reasons For Belief
I think the underlying problem is that people misunderstand what a 'belief' is, thinking that it somehow implies either refusal to change your opinion if you get counter evidence, or that it means thinking something is true without evidence. But a belief can be a perfectly scientific and rational concept. We all hold beliefs on countless different things: whether humans are causing climate change; whether gravity exists; whether it's safe to drink the water out of your tap; whether your next door neighbour is a nice person. These are all beliefs, and we will hold them to different degrees, based on our reasons for holding them.
The strength of your belief in something will be based on how solid you think your reasons are for that belief. This is true regardless of the particular type of reason. What are the possible types?
- Evidence is the obvious one, with the scientific method being the route of choice for evaluating evidence. It's not perfect, but based on results it seems to be the best way we have for testing beliefs against real world data and separating out what is likely to be true from what is likely to be false.
- Faith is the other big one, where people will explicitly admit that they don't have evidence for their belief, but choose to hold it anyway, for whatever their justification is.
- Authority is another common one, and is interesting because it can fall in between evidence and faith. Ideally we would never rely on authority and always insist on evidence, but in practice we often have to. For instance, I will tend to rely on the authority of an expert like Richard Dawkins or Lawrence Krauss or The National Health and Medical Research Council to help determine my beliefs about things within their areas of expertise. On its face this looks like faith, and to a degree it is. But my trust is not based on blind whim or just wanting them to be right, it's based on evidence having supported their previous claims, which increases confidence that they are reliable on other issues within their area of expertise, combined with the fact that I know I can look for specific evidence on these things if I want to. I'm never required to take their word on faith; I'm just using that as a shortcut because I don't have the time to look into the evidence for everything in my world that may or may not be true.
So, for a rational person, the strength of their belief in something will be based on the strength of evidence to support it. This can range from near certainty for extremely well supported theories like general relativity or evolution, or well refuted theories like phlogiston (look it up) or the moon landings being faked. You implicitly use the same method to determine what constitutes a healthy diet, or if your partner is cheating on you, or what the fastest route is to get to work.
(Note that the scientific definition of a fact is generally considered to be something that is so well supported that it would be perverse to deny it. So it's not really anything qualitatively different from a belief, just something so well supported that you'd basically need a damn good reason to expect anyone to waste time questioning it; time is limited and we've all got better things to do!)
I Think Therefore I Believe
But here is the key thing about belief: as soon as you ask yourself whether or not you believe something, you now hold a belief about it.
Up to now, you will not have held a belief one way or the other about whether or not an orange unicorn named Shirley is happily living at the top of Mount Everest, but as soon as I pose the question of whether you believe it or not, you now hold a belief. You effectively weigh up the evidence you have for and against it (which would include things as specific as whether you've heard of this exact thing before to more general things such as knowledge about whether unicorns exist and the survivability of the peak of Mount Everest) and decide whether you believe it is true or believe it is false (hopefully the latter).
The strength of this belief can vary by all kinds of degrees, but you're going to believe something about it, somewhere along the spectrum from absolute certainty that it's false to absolute certainty that it's true. You would have to be the blankest of slates to have absolutely no opinion one way or the other, to have absolutely no knowledge that would make you lean even slightly one way or the other.
So when you ask an atheist what his belief is regarding the existence of a god, the fact of the matter is that this particular belief is not the same as the infinite other possible things that may or may not exist, because he has specifically pondered it. In reality, if you believe that the evidence at all leans towards there being some kind of higher power, then you are a theist, even if you think the evidence is very weak. And if you at all lean towards there not being any kind of higher power, then you are an atheist, and you believe that there is no god. This belief may be weak; you will of course be willing to change it if you are presented with good evidence to the contrary; but it's a belief, not the absence of one.
And this holds true for anyone taking an agnostic stance too. Agnosticism is just the belief that it's not possible to prove the existence of a god one way or the other. This is completely separate to whether you believe a god exists or not. You can hold beliefs without the hope of ever having definitive proof, and quite often you have to do so because you usually have to take action in life with incomplete information. Whether you can get definitive proof or not is generally a moot point because we have to act without definitive proof most of the time.
Consider whether it is knowable or not that the water in your tap is safe to drink. In theory it's knowable, but in practice you do not have certainty and never will. But you either drink it or you don't, and that says what your belief is on the issue. Is your car safe to drive? If you drive it, then you believe it is (to some degree). Can you fly? If you jump off a building and flap your arms then you believe that you can (at least strongly enough to risk your life over it). Do you believe in a god? If you act in a way that you would not if you did not (such as praying or making moral arguments based on sin or the existence of souls), then you believe it. Knowability is just not really relevant in practice.
So I hope with all the previous rambling I've made a reasonable case that 'lack of belief' is really not what atheists have, and that any atheists who read this are more willing to own their actual beliefs without feeling that it compels them to make any claims to certainty, or equates beliefs based on evidence with beliefs based on faith. And for any theists who read this, I hope I've made it a bit clearer that you effectively apply reason and evidence to 100 different things every day, and maybe start to apply the same to your opinions on religion and the existence of supernatural beings.