The theory must not contradict empirical facts.

Well-being and happiness never appeared to me as an absolute aim. I am even inclined to compare such moral aims to the ambitions of a pig.

A great thought begins by seeing something differently, with a shift of the mind's eye.

However we select from nature a complex [of phenomena] using the criterion of simplicity, in no case will its theoretical treatment turn out to be forever appropriate (sufficient).... I do not doubt that the day will come when [general relativity], too, will have to yield to another one, for reasons which at present we do not yet surmise. I believe that this process of deepening theory has no limits.

Scientific research can reduce superstition by encouraging people to think and view things in terms of cause and effect.

To dwell on the things that depress or anger us does not help in overcoming them. One must knock them down alone.

You can't resolve a dilemma with all the very same mind that made it