" Non-Christian philosophers from the time of the Greeks until just before our modern period had three things in common. First, they were rationalists. That is, they assumed that man (though he is finite and limited) can begin from himself and gather enough particulars to make his own universals. Rationalism rejects any knowledge outside of man himself, especially any knowledge from God. "

― Francis A. Schaeffer , How Should We Then Live? The Rise and Decline of Western Thought and Culture