Men's epistemology—or, more precisely, their psycho-epistemology, their method of awareness—is the most fundamental standard by which they can be classified. Few men are consistent in that respect; most men keep switching from one level of awareness to another, according to the circumstances or the issues involved, ranging from moments of full rationality to an almost somnambulistic stupor. But the battle of human history is fought and determined by those who are predominantly consistent, those who, for good or evil, are committed to and motivated by their chosen psycho-epistemology and its corollary view of existence—with echoes responding to them, in support or opposition, in the switching, flickering souls of the others.
A man's method of using his consciousness determines his method of survival. The three contestants are Attila, the Witch Doctor and the Producer—or the man of force, the man of feelings, the man of reason—or the brute, the mystic, the thinker. The rest of mankind calls it expedient to be tossed by the current of events from one of those roles to another, not choosing to identify the fact that those three are the source which determines the current's direction.
Ayn Rand, For The New Intellectual, p. 21.