As soon as science has emerged from its initial stages, theoretical advances are no longer achieved merely by a process of arrangement. Guided by empirical data, the investigator rather develops a system of thought which, in general, is built up logically from a small number of fundamental assumptions, the so-called axioms. We call such a system of thought a theory. The theory finds the justification for its existence in the fact that it correlates a large number of single observations, and it is just here that the 'truth' of the theory lies.

Out of clutter, find simplicity.

One must console oneself with the thought that time has a sieve through which most of these important things run into the ocean of oblivion and what remains after this selection is often still trite and bad.

Non-cooperation in military matters should be an essential moral principle for all true scientists.

You cannot prevent and prepare for war at the same time.

We must not only learn to tolerate our differences. We must welcome them as the richness and diversity which can lead to true intelligence.

The really valuable method of thought to arrive at a logically coherent system is intuition.