Atheism is a conclusion reached by the most reasonable methods and one which is not asserted dogmatically but is explained in its every feature by the light of reason. The atheist does not boast of knowing in a vainglorious, empty sense. He understands by knowledge the most reasonable and clear and sound position one can take on the basis of all the evidence at hand. This evidence convinces him that theism is not true, and his logical position, then, is that of atheism.We repeat that the atheist is one who denies the assumptions of theism. he asserts, in other words, that he doesn’t believe in a God because he has no good reason for believing in a God. That’s atheism — and that’s good sense.
E. Haldeman-Julius, The meaning of atheism