An atheist is one who does not believe in the existence of God or who denies God's existence. The difficulty of defining atheism results from the whole range of nuances that the concept appears to subsume. Whether it results from active denial or whether it derives from a real or supposed vacuum, whether it is therefore “positive” or “negative,” atheism is fundamentally conceived as unbelief. But this only renders the problem more complex: How can one devise a history or a sociology of the “negative”? If atheism, placed as it is under the sign of privacy, is nothing more than the other side of belief, only the latter can be a positive concept. Atheism is thus an integral part of a system organized around a central reference to a religion which exhausts the concept of belief. Ultimately, any sociology of atheism is a sociology of religion.