“Neither acquiescence in skepticism nor acquiescence in dogma is what education should produce. What it should produce is a belief that knowledge is attainable in a measure, though with difficulty; that much of what passes for knowledge at any given time is likely to be more or less mistaken, but that the mistakes can be rectified by care and industry. In acting upon our beliefs, we should be very cautious where a small error would mean disaster; nevertheless it is upon our beliefs that we must act. This state of mind is rather difficult: it requires a high degree of intellectual culture without emotional atrophy. But though difficult, it is not impossible; it is in fact the scientific temper. Knowledge, like other good things, is difficult, but not impossible; the dogmatist forgets the difficulty, the skeptic denies the possibility. Both are mistaken, and their errors, when widespread, produce social disaster.”

Introduction "On The Sources of Knowledge and of Ignorance" Section XVII, p. 30 Variant translation: I believe it is worthwhile trying to discover more about the world, even if this only teaches us how little we know. It might do us good to remember from time to time that, while differing widely in the various little bits we know, in our infinite ignorance we are all equal.
If we thus admit that there is no authority beyond the reach of criticism to be found within the whole province of our knowledge, however far we may have penetrated into the unknown, then we can retain, without risk of dogmatism, the idea that truth itself is beyond all human authority. Indeed, we are not only able to retain this idea, we must retain it. For without it there can be no objective standards of scientific inquiry, no criticism of our conjectured solutions, no groping for the unknown, and no quest for knowledge.
Conjectures and Refutations: The Growth of Scientific Knowledge (1963)

The Essentials of the Art of Medicine. 1897. p 26.

To question genetic intelligence is not racism (2007)
Context: Science is no stranger to controversy. The pursuit of discovery, of knowledge, is often uncomfortable and disconcerting. I have never been one to shy away from stating what I believe to be the truth, however difficult it might prove to be. This has, at times, got me in hot water.
Rarely more so than right now, where I find myself at the centre of a storm of criticism. I can understand much of this reaction. For if I said what I was quoted as saying, then I can only admit that I am bewildered by it. To those who have drawn the inference from my words that Africa, as a continent, is somehow genetically inferior, I can only apologise unreservedly. That is not what I meant. More importantly from my point of view, there is no scientific basis for such a belief.
I have always fiercely defended the position that we should base our view of the world on the state of our knowledge, on fact, and not on what we would like it to be. This is why genetics is so important. For it will lead us to answers to many of the big and difficult questions that have troubled people for hundreds, if not thousands, of years.
But those answers may not be easy, for, as I know all too well, genetics can be cruel. My own son may be one of its victims. Warm and perceptive at the age of 37, Rufus cannot lead an independent life because of schizophrenia, lacking the ability to engage in day-to-day activities.

"The Hermeneutics of Suspicion: Recovering Marx, Nietzsche, and Freud"

Source: The Social Construction of Reality, 1966, p. 65

Visions of Politics (2002), "Interpretation, rationality and truth"

Source: Computation and cognition, 1984, p. 130

1910s, The Progressives, Past and Present (1910)