An idea is a feat of association, and the height of it is a good metaphor.

A new and valid idea is worth more than a regiment and fewer men can furnish the former than command the latter.

A new idea is first condemned as ridiculous and then dismissed as trivial, until finally, it becomes what everybody knows.

There is no prosperity, trade, art, city, or great material wealth of any kind, but if you trace it home, you will find it rooted in a thought of some individual man.

Not just in commerce but in the world of ideas too our age is putting on a veritable clearance sale. Everything can be had so dirt cheap that one begins to wander whether in the end anyone will want to make a bid.

Ideas are refined and multiplied in the commerce of minds. In their splendor, images effect a very simple communion of souls.

Greater than the tread of mighty armies is an idea whose time has come.

Concepts, like individuals, have their histories and are just as incapable of withstanding the ravages of time as are individuals. But in and through all this they retain a kind of homesickness for the scenes of their childhood.

In every great time there is some one idea at work which is more powerful than any other, and which shapes the events of the time and determines their ultimate issues.

Ideas too are a life and a world.