Atheist: 'I hear the voice of conscience, but I deny the reality of God.' St. Thomas: 'That is like listening to someone speak, but denying that anyone is there.' Atheist: 'That's right; nobody is.' St. Thomas: 'Then you deny not only God but conscience, because you consider it a hallucination.' Atheist: 'I misspoke. What I meant to say is that when I am listening to conscience, I am really listening to myself.' St. Thomas: 'Then you still deny conscience, because you deny its authority to judge you. Instead you claim to judge yourself, but no one can be judge in his own case.
J. Budziszewski, Commentary on Thomas Aquinas's Treatise on Law
atheism, conscience