Only passion can control passion, and only a contrary impulse or desire can check impulse. Reason, as it is preached by traditional moralists, is too of negative, too little living, to make a good life. It is not by reason alone that wars can be prevented, but by a positive life of impulses and passions antagonistic to those that lead to war. It is the life of impulse that needs to be changed, not only the life of conscious thought.
Source: Principles fo Social Reconstrucition, 1916, chapt.1: the principles of growth
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