All great progress takes place when two sciences come together, and when their resemblance proclaims itself, despite the apparent disparity of their substance.

Experiment is the sole source of truth.

Thus, be it understood, to demonstrate a theorem, it is neither necessary nor even advantageous to know what it means.

Sociology is the science with the greatest number of methods and the least results.

Often when works at a hard question, nothing good is accomplished at the first attack. Then one takes a rest, long or short, and sits down anew to the work. During the first half-hour, as before, nothing is found, and then all of a sudden the decisive idea presents itself to the mind.

All that is not thought is pure nothingness; since we can think only thoughts, and all the words we use to speak of things can express only thoughts, to say there is something other than thought is therefore an affirmation which can have no meaning.

But for harmony beautiful to contemplate, science would not be worth following.