The correct characterisation of the opposition between theism and atheism is therefore this: the theist has existential beliefs, metaphysical beliefs, of a certain distinctive kind; and the atheist does not share them, and therefore does not even begin to enter the domain of discourse in which these beliefs have their life and content. Rather to use a by now familiar simile, but it exactly captures the point - atheism is to theism as not-collecting stamps is to stamp collecting. Not collecting stamps is not a hobby. It says nothing about the non-stamp-collector's other hobbies or interests. It denotes only the open-ended and negative state of not-collecting-stamps. To think of non-stamp-collectors as theists think of atheists, stamp collectors would have to think that non-stamp-collectors have stamp interests of (so to speak) a positively negative kind; that they share their own obsessions and interests about stamps but in reverse, for example in the form of hating stamps, deliberately doing stamp-related non-stamp-collecting things, and the like."
from "The God Argument" by A C Grayling.