1. People are invariably surprised to hear me say I am both an atheist and an agnostic, as if this somehow weakens my certainty. I usually reply with a question like, 'Well, are you a Republican or an American?' The two words serve different concepts and are not mutually exclusive. Agnosticism addresses knowledge; atheism addresses belief. The agnostic says, 'I don't have a knowledge that God exists.' The atheist says, 'I don't have a belief that God exists.' You can say both things at the same time. Some agnostics are atheistic and some are theistic.
Godless: How an Evangelical Preacher Became One of America's Leading Atheists
2. Scientists do not join hands every Sunday and sing "Yes gravity is real! I know gravity is real! I will have faith! I believe in my heart that what goes up, up, up must come down, down, down. Amen!" If they did, we would think they were pretty insecure about the concept.
Godless: How an Evangelical Preacher Became One of America's Leading Atheists