The Clarity of God's Existence examines the need for theistic proofs within historic Christianity, and the challenges to these since the Enlightenment. Historically (and scripturally), Christianity has maintained that unbelief is inexcusable. If failing to know God is a sin, the implication is that humans can and should know God. Humans should know God because his eternal power and divine nature are clearly revealed in the things that are made. And yet, Anderson argues, more time is spent on avoiding the need for clarity to establish inexcusability than on actually providing an argument or proof. Proofs that rely on Aristotle or Plato and that establish a Prime Mover or designer are thought to be sufficient. But the adequacy of these, not only to prove the God of theism, but also to prove anything at all, has been called into question by Enlightenment thinkers like David Hume.