Whenever we ask questions in philosophy it is important to remember that context always matters. Asking whether God exists in a Benedictine monastery is different than asking the same question at the annual Skeptics convention. When we ask that question in the United States in 2011, even regional geography can make a difference, as can education level and more to the point, educational specialty.
Philosophers, for example, tend to have definite attitudes to religious belief, which is not, of course, exactly the same thing as belief in God. In my experience a larger percentage of professional philosophers are atheists or agnostics than one finds in the general population, and those who believe tend to fall into two quite different camps: what I call the vague/symbolic liberal believers who embrace social justice and peace and remain self-consciously reserved about doctrinal commitment, arguing for example that one must read the bible critically, understanding that many of the things more fundamentalist believers take literally are to be understood 'symbolically' or 'metaphorically'. In the other camp are those who self-identify as Christian, or Jewish, or Muslim, etc., philosophers, with the 'Christian' added, not as a hyphenated equal term but as a qualifier/modifier of the 'philosopher' term. Sure, they are philosophers, but their philosophy is carried on in the context of their Christian belief; conversely, they are Christians, but ones who take a more reasoned, argument-driven stance with respect to their beliefs. Actually, most such philosophers use reason to defend their beliefs, marshalling arguments in favor of beliefs already held for other reasons, or they argue that whatever it is that they believe is true and can be proven to be so by using unbiassed rational argument. In all these cases the idea is that reason is useful and dependable but that its usefulness and dependability are a function of its origin in the divine plan. Properly used, reason can never disprove religious truth; whenever reason is used in a skeptical way it is being perverted and such reasoning must itself be flawed.
But philosophers make up a miniscule percentage of American adults. There are certainly no more than 8,000 to 10,000 people who make a living teaching philosophy, out of a working population of more than 153 million. So, what philosophers think is not terribly important, especially since, despite their presence on every college and university faculty, they have very little public presence in the culture, and arguably even less influence.
But 'ordinary' people, who are not professional philosophers, definitely have ideas about religion and about God, and in this chapter we will examine both the classical philosopher's arguments about God as well as popular beliefs about the issue. Both are useful and important and in this case much of what philosophers say about God mirrors or summarizes what regular folks think, so there is an interesting crossover.
Before we start the exposition I need to interject something less certain. It is my experience that many Americans who are counted among believers, and many of who self-identify as non-affiliated with any religion, share vague, often somewhat unorthodox images of the divine, which make an awkward fit with the Being whose existence is proved -- or not -- by the classical arguments. So, many of the classical arguments might be about a God who bears little resemblance to the one you worship/uneasily think you should worship/would like to forget, but cannot.
Also, many straight-aherad believers also experience a large conceptual gap between their God - often instantiated as Jesus -- and the God discussed in formal proofs for God's existence.
We will address these issues along the way because I think they matter.
A final preparatory note: in 2010, 1.5% of Americans called themselves atheist/agnostic, up considerably from the 0.9% who so described themselves as such in 2001. This could be a function of the recent economic downturn -- that is purely guesswork -- but in any case there aren't many atheists in the US of A, and so the whole issue of why we bother with proofs of God's existence is also a very live question, with which we will begin our consideration of the formal proofs for God's existence.
First: Why offer proofs when almost all of us already believe?