The God Delusion struck me as a sort of primer for those new to atheism. It is mostly a discussion of the arguments in favor of theism and his response to them, though he does have a chapter where he discusses why he thinks it's almost certain that god does not exist. The motivation for the book strikes me as a way to collect the most common arguments for and against god into one volume.
"Well, evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts don't go away when scientists debate rival theories to explain them. Einstein's theory of gravitation replaced Newton's in this century, but apples didn't suspend themselves in midair, pending the outcome. And humans evolved from ape- like ancestors whether they did so by Darwin's proposed mechanism or by some other yet to be discovered."
-Stephen Jay Gould
-Stephen Jay Gould
