There is no pure, disinterested, theory-free observation.

Our aim as scientists is objective truth; more truth, more interesting truth, more intelligible truth. We cannot reasonably aim at certainty. Once we realize that human knowledge is fallible, we realize also that we can never be completely certain that we have not made a mistake.

It is part of my thesis that all our knowledge grows only through the correcting of our mistakes.

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.

You cannot have a rational discussion with a man who prefers shooting you to being convinced by you.

We know a great deal, but our ignorance is sobering and boundless. With each step forward, with each problem which we solve, we not only discover new and unsolved problems, but we also discover that where we believed that we were standing on firm and safe ground, all things are, in truth, insecure and in a state of flux.

No number of sightings of white swans can prove the theory that all swans are white. The sighting of just one black one may disprove it.