Definitions.... are never really needed, and rarely of any use

Whenever a theory appears to you as the only possible one, take this as a sign that you have neither understood the theory nor the problem which it was intended to solve.

Science is the century-old endeavour to bring together by means of systematic thought the perceptible phenomena of this world into as thorough-going an association as possible. To put it boldly, it is the attempt at a posterior reconstruction of existence by the process of conceptualization. Science can only ascertain what is, but not what should be, and outside of its domain value judgements of all kinds remain necessary.

Our knowledge can only be finite, while our ignorance must necessarily be infinite.

There is an almost universal tendency, perhaps an inborn tendency, to suspect the good faith of a man who holds opinions that differ from our own opinions. It obviously endangers the freedom and the objectivity of our discussion if we attack a person instead of attacking an opinion or, more precisely, a theory.

In my view, aiming at simplicity and lucidity is a moral duty of all intellectuals: lack of clarity is a sin, and pretentiousness is a crime.

[The aim of science is] to explain what so far has taken to be an explicans, such as a law of nature. The task of empirical science constantly renews itself. We may go on forever, proceeding to explanations of a higher and higher universality.