De fide rerum invisibilium
De fide rerum invisibilium (On Faith in the Unseen) is a work by Saint Augustine composed around 400 A.D. It is also referred to as De fide rerum quae non videntur (On Faith in that which cannot be seen). It is thought to be based on a sermon. The work is an answer to those who demand empirical proof and claim that Christianity is contrary to reason.