This article attempts to provide a general introduction to atheism. Whilst I have tried to be as neutral as possible regarding contentious issues, you should always remember that this document represents only one viewpoint. I would encourage you to read widely and draw your own conclusions; some relevant books are listed in a companion document: Atheist Resources.
To provide a sense of cohesion and progression, I have presented this article as an imaginary conversation between an atheist and a theist. All the questions asked by the imaginary theist are questions which have been cropped up repeatedly on the Usenet newsgroup alt.atheism since that newsgroup was first created. Some other frequently asked questions are answered in a companion document: Atheist Arguments.
Please note that this article is arguably slanted towards answering questions posed from a Christian viewpoint. This is because the FAQ files reflect questions which have actually been asked, and it is predominantly Christians who proselytize on alt.atheism.
So when I talk of religion, I am talking primarily about religions such as Christianity, Judaism and Islam, which involve some sort of superhuman divine being. Much of the discussion will apply to other religions, but some of it may not. (See Definition of a "cult.")
"What is atheism?"
Atheism is characterized by an absence of belief in the existence of gods. This absence of belief generally comes about either through deliberate choice, or from an inherent inability to believe religious teachings which seem literally incredible. It is not a lack of belief born out of simple ignorance of religious teachings.
Some atheists go beyond a mere absence of belief in gods: they actively believe that particular gods, or all gods, do not exist. Just lacking belief in Gods is often referred to as the "weak atheist" position; whereas believing that gods do not (or cannot) exist is known as "strong atheism."
Regarding people who have never been exposed to the concept of 'god': Whether they are 'atheists' or not is a matter of debate. Since you're unlikely to meet anyone who has never encountered religion, it's not a very important debate...
It is important, however, to note the difference between the strong and weak atheist positions. "Weak atheism" is simple skepticism; disbelief in the existence of God. "Strong atheism" is an explicitly held belief that God does not exist. Please do not fall into the trap of assuming that all atheists are "strong atheists." There is a qualitative difference in the "strong" and "weak" positions; it's not just a matter of degree.
Some atheists believe in the nonexistence of all Gods; others limit their atheism to specific Gods, such as the Christian God, rather than making flat-out denials.
"But isn't disbelieving in God the same thing as not believing God exists?"
Definitely not. Disbelief in a proposition means that one does not believe it to be true. Not believing that something is true is not equivalent to believing that it is false; one may simply have no idea whether it is true or not. Which brings us to agnosticism.
"What is agnosticism then?"
The term 'agnosticism' was coined by Professor T.H. Huxley at a meeting of the Metaphysical Society in 1876. He defined an "agnostic" as someone who disclaimed both ("strong") atheism and theism, and who believed that the question of whether a higher power existed was unsolved and insoluble. Another way of putting it is that an agnostic is someone who believes that we do not know for sure whether God exists. Some agnostics believe that we can never know.
In recent years, however, the term agnostic has also been used to describe those who simply believe that the evidence for or against God is inconclusive, and therefore are undecided about the issue.
To reduce the amount of confusion over the use of term agnosticism, it is recommended that usage based on a belief that we cannot know whether God exists be qualified as "strict agnosticism" and usage based on the belief that we merely do not know yet be qualified as "empirical agnosticism."
Words are slippery things, and language is inexact. Beware of assuming that you can work out someone's philosophical point of view simply from the fact that she calls herself an atheist or an agnostic. For example, many people use agnosticism to mean what is referred to here as "weak atheism," and use the word "atheism" only when referring to "strong atheism."
Beware also that because the word "atheist" has so many shades of meaning that it is very difficult to generalize about atheists. About all you can say for sure is that atheists don't believe in God. For example, it certainly isn't the case that all atheists believe that science is the best way to find out about the universe.
"What about the term 'freethinker'? What does that mean?"
A freethinker is one who thinks freely--one who is prepared to consider any possibility, and who determines which ideas are right or wrong by bringing reason to bear, according to a consistent set of rules such as the scientific method.
The Freedom From Religion Foundation has a "nontract" on what it means to be a freethinker, at: http://www.ffrf.org/nontracts/freethinker.php.
"So what is the philosophical justification or basis for atheism?"
There are many philosophical justifications for atheism. To find out why a particular person chooses to be an atheist, it's best to ask her.
Many atheists feel that the idea of God as presented by the major religions is essentially self-contradictory, and that it is logically impossible that such a God could exist. Others are atheists through skepticism, because they see no evidence that God exists.
There are a number of books which lay out a philosophical justification for atheism, such as Martin's Atheism: A Philosophical Justification and Smith's Atheism: The Case Against God. A few such books are in the document listing Atheist Media.
Of course, some people are atheists without having any particular logical argument to back up their atheism. For some, it is simply the most comfortable, common sense position to take.
"But isn't it impossible to prove the nonexistence of something?"
There are many counterexamples to such a statement. For example, it is quite simple to prove that there does not exist a prime number larger than all other prime numbers. Of course, this deals with well-defined objects obeying well-defined rules. Whether Gods or universes are similarly well-defined is a matter for debate.
However, assuming for the moment that the existence of a God is not provably impossible, there are still subtle reasons for assuming the nonexistence of God. If we assume that something does not exist, it is always possible to show that this assumption is invalid by finding a single counterexample.
If on the other hand we assume that something does exist, and if the thing in question is not provably impossible, showing that the assumption is invalid may require an exhaustive search of all possible places where such a thing might be found, to show that it isn't there. Such an exhaustive search is often impractical or impossible. There is no such problem with largest primes, because we can prove that they don't exist.
Therefore it is generally accepted that we must assume things do not exist unless we have evidence that they do. Even theists follow this rule most of the time; they don't believe in unicorns, even though they can't conclusively prove that no unicorns exist anywhere.
To assume that God exists is to make an assumption which probably cannot be tested. We cannot make an exhaustive search of everywhere God might be to prove that he doesn't exist anywhere. So the skeptical atheist assumes by default that God does not exist, since that is an assumption we can test.
Those who profess strong atheism usually do not claim that no sort of God exists; instead, they generally restrict their claims so as to cover varieties of God described by followers of various religions. So whilst it may be impossible to prove conclusively that no God exists, it may be possible to prove that (say) a God as described by a particular religious book does not exist. It may even be possible to prove that no God described by any present-day religion exists.
In practice, believing that no God described by any religion exists is very close to believing that no God exists. However, it is sufficiently different that counterarguments based on the impossibility of disproving every kind of God are not really applicable.
"But what if God is essentially nondetectable?"
If God interacts with our universe in any way, the effects of his interaction must have some physical manifestation. Hence his interaction with our universe must be in principle detectable.
If God is essentially nondetectable, it must therefore be the case that he does not interact with our universe in any way. Many atheists would argue that if God does not interact with our universe at all, it is of no importance whether he exists or not. A thing which cannot even be detected in principle does not logically exist.
Of course, it could be that God is detectable in principle, and that we merely cannot detect him in practice. However, if the Bible is to be believed, God was easily detectable by the Israelites. Surely he should still be detectable today? Why has the situation changed?
Note that I am not demanding that God interact in a scientifically verifiable, physical way. I might potentially receive some revelation, some direct experience of God. An experience like that would be incommunicable, and not subject to scientific verification--but it would nevertheless be as compelling as any evidence can be.
But whether by direct revelation or by observation, it must surely be possible to perceive some effect caused by God's presence; otherwise, how can I distinguish him from all the other things that don't exist?
"God is unique. He is the supreme being, the creator of the universe. He must by definition exist."
Things do not exist merely because they have been defined to do so. We know a lot about the definition of Santa Claus--what he looks like, what he does, where he lives, what his reindeer are called, and so on. But that still doesn't mean that Santa exists.
"Then what if I managed to logically prove that God exists?"
Firstly, before you begin your proof, you must come up with a clear and precise definition of exactly what you mean by "God." A logical proof requires a clear definition of that which you are trying to prove.
"But everyone knows what is meant by 'God'!"
Different religions have very different ideas of what 'God' is like; they even disagree about basic issues such as how many gods there are, whether they're male or female, and so on. An atheist's idea of what people mean by the word 'God' may be very different from your own views.
"OK, so if I define what I mean by 'God,' and then logically prove he exists, will that be enough for you?"
Even after centuries of effort, nobody has come up with a watertight logical proof of the existence of God. In spite of this, however, people often feel that they can logically prove that God exists.
Unfortunately, reality is not decided by logic. Even if you could rigorously prove that God exists, it wouldn't actually get you very far. It could be that your logical rules do not always preserve truth--that your system of logic is flawed. It could be that your premises are wrong. It could even be that reality is not logically consistent. In the end, the only way to find out what is really going on is to observe it. Logic can merely give you an idea where or how to look; and most logical arguments about God don't even perform that task.
Logic is a useful tool for analyzing data and inferring what is going on; but if logic and reality disagree, reality wins.
"Then it seems to me that nothing will ever convince you that God exists."
A clear definition of 'God,' plus some objective and compelling supporting evidence, would be enough to convince many atheists.
The evidence must be objective, though; anecdotal evidence of other people's religious experiences isn't good enough. And strong, compelling evidence is required, because the existence of God is an extraordinary claim--and extraordinary claims require extraordinary evidence.
"OK, you may think there's a philosophical justification for atheism, but isn't it still a religious belief?"
One of the most common pastimes in philosophical discussion is "the redefinition game." The cynical view of this game is as follows:
Person A begins by making a contentious statement. When person B points out that it can't be true, person A gradually redefines the words he used in the statement until he arrives at something person B is prepared to accept. He then records the statement, along with the fact that person B has agreed to it, and continues. Eventually A uses the statement as an "agreed fact," but uses his original definitions of all the words in it rather than the obscure redefinitions originally needed to get B to agree to it. Rather than be seen to be apparently inconsistent, B will tend to play along.
The point of this digression is that the answer to the question "Isn't atheism a religious belief?" depends crucially upon what is meant by "religious." "Religion" is generally characterized by belief in a superhuman controlling power--especially in some sort of God--and by faith and worship.
(It's worth pointing out in passing that some varieties of Buddhism are not "religion" according to such a definition.)
Atheism is certainly not a belief in any sort of superhuman power, nor is it categorized by worship in any meaningful sense. Widening the definition of "religious" to encompass atheism tends to result in many other aspects of human behavior suddenly becoming classed as "religious" as well--such as science, politics, and watching TV.
"OK, maybe it's not a religion in the strict sense of the word. But surely belief in atheism (or science) is still just an act of faith, like religion is?"
Firstly, it's not entirely clear that skeptical atheism is something one actually believes in.
Secondly, it is necessary to adopt a number of core beliefs or assumptions to make some sort of sense out of the sensory data we experience. Most atheists try to adopt as few core beliefs as possible; and even those are subject to questioning if experience throws them into doubt.
Science has a number of core assumptions. For example, it is generally assumed that the laws of physics are the same for all observers (or at least, all observers in inertial frames). These are the sort of core assumptions atheists make. If such basic ideas are called "acts of faith," then almost everything we know must be said to be based on acts of faith, and the term loses its meaning.
Faith is more often used to refer to complete, certain belief in something. According to such a definition, atheism and science are certainly not acts of faith. Of course, individual atheists or scientists can be as dogmatic as religious followers when claiming that something is "certain." This is not a general tendency, however; there are many atheists who would be reluctant to state with certainty that the universe exists.
Faith is also used to refer to belief without supporting evidence or proof. Skeptical atheism certainly doesn't fit that definition, as skeptical atheism has no beliefs. Strong atheism is closer, but still doesn't really match, as even the most dogmatic atheist will tend to refer to experimental data (or the lack of it) when asserting that God does not exist.
"If atheism is not religious, surely it's antireligious?"
It is an unfortunate human tendency to label everyone as either "for" or "against," "friend" or "enemy." The truth is not so clear-cut.
Atheism is the position that runs logically counter to theism; in that sense, it can be said to be "antireligion." However, when religious believers speak of atheists being "antireligious" they usually mean that the atheists have some sort of antipathy or hatred towards theists.
This categorization of atheists as hostile towards religion is quite unfair. Atheist attitudes towards theists in fact cover a broad spectrum.
Most atheists take a "live and let live" attitude. Unless questioned, they will not usually mention their atheism, except perhaps to close friends. Of course, this may be in part because atheism is not "socially acceptable" in many countries.
A few atheists are quite antireligious, and may even try to "convert" others when possible. Historically, such antireligious atheists have made little impact on society outside the Eastern Bloc countries.
(To digress slightly: the Soviet Union was originally dedicated to separation of church and state, just like the USA. Soviet citizens were legally free to worship as they wished. The institution of "state atheism" came about when Stalin took control of the Soviet Union and tried to destroy the churches in order to gain complete power over the population.)
Some atheists are quite vocal about their beliefs, but only where they see religion encroaching on matters which are not its business--for example, the government of the USA. Such individuals are usually concerned that church and state should remain separate.
"But if you don't allow religion to have a say in the running of the state, surely that's the same as state atheism?"
The principle of the separation of church and state is that the state shall not legislate concerning matters of religious belief. In particular, it means not only that the state cannot promote one religion at the expense of another, but also that it cannot promote any belief which is religious in nature.
Religions can still have a say in discussion of purely secular matters. For example, religious believers have historically been responsible for encouraging many political reforms. Even today, many organizations campaigning for an increase in spending on foreign aid are founded as religious campaigns. So long as they campaign concerning secular matters, and so long as they do not discriminate on religious grounds, most atheists are quite happy to see them have their say.
"What about prayer in schools? If there's no God, why do you care if people pray?"
Because people who do pray are voters and lawmakers, and tend to do things that those who don't pray can't just ignore. Also, Christian prayer in schools is intimidating to non-Christians, even if they are told that they need not join in. It is particularly bad if the prayer is led by a teacher, or otherwise officially endorsed.
The diversity of religious and nonreligious belief means that it is impossible to formulate a meaningful prayer that will be acceptable to all those present at any public event.
This is one reason why the public school system in the USA is not permitted to endorse particular religious beliefs through official prayer time in schools. Children are, of course, quite free to pray as they wish in their free time; there is no question of trying to prevent prayer from happening in schools.
"You mentioned Christians who campaign for increased foreign aid. What about atheists? Why aren't there any atheist charities or hospitals? Don't atheists object to the religious charities?"
There are many charities without religious purpose that atheists can contribute to. Some atheists contribute to religious charities as well, for the sake of the practical good they do. Some atheists even do voluntary work for charities founded on a theistic basis.
Most atheists seem to feel that atheism isn't worth shouting about in connection with charity. To them, atheism is just a simple, obvious everyday matter, and so is charity. Many feel that it's somewhat cheap, not to say self-righteous, to use simple charity as an excuse to plug a particular set of religious beliefs.
To "weak" atheists, building a hospital to say "I do not believe in God" is a rather strange idea; it's rather like holding a party to say "Today is not my birthday." Why the fuss? Atheism is rarely evangelistic.
"You said atheism isn't antireligious. But is it perhaps a backlash against one's upbringing, a way of rebelling?"