The question of how and why we believe things is a crucial point of disagreement between atheists and theists. Atheists say believers are overly credulous, believing things much too easily and readily than reason or logic can justify. Theists say nonbelievers deliberately disregard important evidence and are thus unjustifiably skeptical. Some theists even say that nonbelievers know that there is a god or that there is evidence proving a god but willfully ignore this knowledge and believe the opposite due to rebellion, pain, or some other cause.
Beneath these surface disagreements is a more fundamental dispute over the nature of belief is and what causes it. A better understanding of how a person arrives at a belief can illuminate whether or not atheists are overly skeptical or theists are overly credulous. It can also help both atheists and theist better frame their arguments in their attempt to reach each other.
Voluntarism, Religion, and Christianity
According to Terence Penelhum, there are two general schools of thought when it comes to how beliefs originate: voluntarist and involuntarist. The voluntarists take say that belief is a matter of will: we have control over what we believe much in the way we have control over our actions. Theists often seem to be voluntarists and Christians in particular commonly argue the voluntarist position.
As a matter of fact, some of history's most prolific theologians like Thomas Aquinas and Soren Kierkegaard have written that believing or at least believing religious dogma is a free act of will. This shouldn't be unexpected, because only if we can be held morally responsible for our beliefs can disbelief be treated as a sin. It isn't possible to defend the idea of atheists going to hell unless they can be held morally accountable for their atheism.
Often, though, the voluntarist position of Christians is modified by the "paradox of grace." This paradox ascribes to us the responsibility to choose to believe the uncertainties of Christian doctrine, but then ascribes the actual power to do so to God. We are morally responsible for choosing to try, but God is responsible for our success. This idea goes back to Paul who wrote that what he did was not done by his own power but because of the Spirit of God within him.
Despite this paradox, Christianity still generally relies upon a voluntarist position of belief because the responsibility lies with the individual to choose the uncertain even impossible belief. Atheists are faced with this when evangelists exhort others to "just believe" and to "choose Jesus." It is they who regularly claim that our atheism is a sin and a path to hell.
Involuntarism & Belief
Involuntarists argue that we cannot really choose to just believe anything. According to involuntarism, a belief is not an action and, hence, cannot be attained by command either by your own or by another's to you.
I haven't noticed a trend among atheists towards either voluntarism or involuntarism. Personally, though, I tend strongly towards involuntarism. It is common for Christian evangelists to try tell me that I have chosen to be an atheist and that I will be punished for this; choosing Christianity, though, will save me.
I try to explain to them that I do not in fact "choose" atheism. Instead, atheism is the only possible position given my present state of knowledge. I can no more "choose" to just believe in the existence of a god than I can choose to believe that this computer doesn't exist. Belief requires good reasons, and although people may differ on what constitutes "good reasons," it is those reasons which cause belief, not choice.
Language & Belief
"... Now I'll give you something to believe. I'm just one hundred and one, five months and a day."
"I can't believe that!" said Alice.
"Can't you?" the Queen said in a pitying tone. "Try again: draw a long breath, and shut your eyes."
Alice laughed. "There's no use trying," she said "one can't believe impossible things."
"I daresay you haven't had much practice," said the Queen. "When I was your age, I always did it for half-an-hour a day. Why, sometimes I've believed as many as six impossible things before breakfast..."
- Lewis Caroll, Through the Looking Glass
This passage from Lewis Caroll's book Through the Looking Glass emphasizes important issues regarding the nature of belief. Alice is a skeptic and, perhaps, an involuntarist she doesn't see how she can be commanded to believe something, at least if she finds it to be impossible. The Queen is a voluntarist who thinks belief is simply an act of will which Alice should be capable of achieving if she tries hard enough and she pities Alice for her failure. The Queen treats belief like an action: attainable with effort.
The language we use provides interesting clues as to whether or not belief is something we can choose by an act of will. Unfortunately, many of the things we say don't make much sense unless both of them are true thus leading to confusion.
For example, we often hear about people preferring to believe one thing or an other, about people being inclined to believe one thing or another, and about people finding it difficult or easy to believe one thing or another. All of this implies that belief is something chosen and suggests that our choices are influenced by our desires and emotions.
Such idioms are not followed consistently in how we discuss belief, though. A good example is that the alternative to beliefs we prefer are not beliefs we don't prefer, but beliefs we find impossible. If a belief is impossible, then the opposite is not something we simply choose: it is the only option, something we are forced to accept.
Contrary to the claims of Christian evangelists, even when we do describe a belief as hard to achieve, we do not normally say that believing in the face of such obstacles is praiseworthy. Rather, the beliefs people tend to be "proudest" of are those which they also say no one can deny. If no one can deny something, then it isn't a choice to believe it. Similarly, we can disagree with the Queen and say that if something is impossible, then choosing to believe it isn't one which any rational person can make.