Pope Francis' encyclical The Light of Faith (LF) obviously presents faith as a light which illuminates realities, enabling the believer to see and understand them. This light, the pope says, "is capable of illuminating every aspect of human existence" (LF4). It is a light that does not come from ourselves because it is a light that shows us reality, not some figment of our own imagination.

One of the most brilliant mathematicians of the late 19th century was the Englishman William Kingdon Clifford. Clifford also dabbled in philosophy and was noted for expounding this principle: "It is wrong always, everywhere and for anyone to believe anything on insufficient evidence." That is, you should never believe something merely because you think it is true or on the basis of evidence that is anything less than indubitable. Applying Clifford's principle would lead one into a most humourless existence with one ever seeking to find sufficient evidence for the truth of even our most mundane beliefs.