(1) A flaw in enlightenment philosophy is the attempt to get moral principles from pure Reason.
Pure Reason does not tell us much. It does not even tell us what axioms are "reasonable" to start with.. It is more like a tool to constrain. It can tell us when we are making a mistake. This is the point of David Hume that got this idea from his experience as a teacher of Euclid's Elements (Geometry.) The axioms were not derived by reason. But they were reasonable. The only function of reason in the Elements was to show when some idea could be shown to be in contradiction to one of the axioms.
There might be reasonable moral principles, but they are not derivable by mean of pure reason which can tell us they way things are, not how they ought to be. That is the famous rule of Hume: You can not derive an "ought" from an "is"
(2) What I am getting at is that faith is a source of knowledge that is different from reason. [This is a doctrine of the Kant-Friesian School]. But even those that are adherents of this school often seem to miss out that this is not a form of psychologism. While it is true with Fries that one needs to look into one's own mind to see what the beginning axioms are that does not mean that the mind knows these things by some kind of implanted knowledge. Rather the mind perceives them but not by reason but by a sort of knowledge that is not sensed nor known by reason. It is non intuitive immediate knowledge.
(3) This was of course obvious in the Middle Ages. The need for faith and reason together was obvious to all. This insight was lost until the Kant Friesian School arose.
