All means prove but blunt instruments, if they have not behind them a living spirit.

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.

Truly novel inventions emerge only in one's youth. Later one becomes ever more experienced, famous-and foolish.

It is impossible to get anywhere without sinning against reason.

I believe that pipe smoking contributes to a somewhat calm and objective judgement in all human affairs.

I don't teach my students, I provide the circumstances in which they can learn.

The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it.