The ideas of economists and political philosophers, both when they are right and when
they are wrong, are more powerful than is commonly understood. Indeed the world is
ruled by little else. Practical men, who believe themselves to be quite exempt from any
intellectual influence, 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. Not, indeed,
immediately but after a certain interval; for in the field of economic and political
philosophy there are not many who are influenced by new theories after they are
twenty-five or thirty years of age, so that the ideas which civil servants and politicians
and even agitators apply to current events are not likely to be the newest. But, soon or
late, it is ideas, not vested interests, which are dangerous for good or evil.
— John Maynard Keynes