John Maynard Keynes on the power of ideas

The ideas of economists and political philosophers, both when they are right and when they are wrong, are more powerful than commonly understood.  Indeed the world is ruled by little else.  Practical men, who believe themselves quite exempt from any intellectual influences, are usually the slaves of some defunct economist.  Madmen in authority, who hear voices in the air, are distilling their frenzy from some academic scribbler of a few years back.  I am sure that the power of vested interests is vastly exaggerated compared with the gradual encroachment of ideas.

~ John Maynard Keynes, The General Theory