Yet the first of many answers is surely the most obvious fact that if man is so much the creature of his custom no reason would prevail save where they proved inadequate.

If thought is simply a reserve power in society, its strength must obviously depend upon common acceptance; and that can only come when some routine has failed to satisfy the impulses of men.

But we may urge a difficulty that is even more decisive.

No system of habits can ever hope to endure long in a world where the cumulative power of memory enables change to be so swift; and no system of habits can endure at all unless its underlying idea represents the satisfaction of a general desire.

It must, that is to say, make rational appeal; and, indeed, as Aristotle said, it can have virtue only to the point where it is conscious of itself.