Biologist Richard Dawkins, a vocal atheist and critic of organized religion, inadvertently revealed the lack of certainty that must accompany all denials of God's existence in his 2006 book The God Delusion.

On a scale of 1 to 7, where 1 is certitude that God exists and 7 is certitude that God does not exist, Dawkins rates himself a 6: "I cannot know for certain, but I think God is very improbable, and I live my life on the assumption that he is not there."