A young man must let his ideas grow, not be continually rooting them up to see how they are getting on.

One has to be a lowbrow, a bit of a murderer, to be a politician, ready and willing to see people sacrificed, slaughtered, for the sake of an idea, whether a good one or a bad one.

Great ideas are not charitable.

Beware thoughts that come in the night. They aren't turned properly; they come in askew, free of sense and restriction, deriving from the most remote of sources.

It is one thing to study historically the ideas which have influenced our predecessors, and another thing to seek in them an influence fruitful for ourselves.

The chief enemy of peace is the spirit of unreason itself: an inability to conceive alternatives, an unwillingness to reconsider old prejudices, to part with ideological obsessions, to entertain new ideas or to improve new plans.

Those for whom words have lost their value are likely to find that ideas have also lost their value.

You cannot put a rope around the neck of an idea; you cannot put an idea up against a barrack-square wall and riddle it with bullets; you cannot confine it in the strongest prison cell that your slaves could ever build.

The secret of living is to find a pivot, the pivot of a concept on which you can make your stand.

General and abstract ideas are the source of the greatest errors of mankind.