“I have therefore found it necessary to deny knowledge in order to make room for faith.”

Source: The Life of the Mind (1971/1978), p. 14.

The Value of Science (1955)
Context: The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn’t know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is still in some doubt. We have found it of paramount importance that in order to progress we must recognize our ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, but none absolutely certain. Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don’t know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.

Thoughts Upon Slavery (1774)
Context: I deny that villany is ever necessary. It is impossible that it should ever be necessary for any reasonable creature to violate all the laws of justice, mercy, and truth. No circumstances can make it necessary for a man to burst in sunder all the ties of humanity. It can never be necessary for a rational being to sink himself below a brute. A man can be under no necessity of degrading himself into a wolf. The absurdity of the supposition is so glaring, that one would wonder any one can help seeing it.

Money.
Notes from Life (1853)

Context: I make this chief distinction between religion and superstition, that the latter is founded on ignorance, the former on knowledge; this, I take it, is the reason why Christians are distinguished from the rest of the world, not by faith, nor by charity, nor by the other fruits of the Holy Spirit, but solely by their opinions, inasmuch as they defend their cause, like everyone else, by miracles, that is by ignorance, which is the source of all malice; thus they turn a faith, which may be true, into superstition.

Letter 21 (73) to Henry Oldenburg , November (1675)

Source: The Stars My Destination

Du wolltest die Philosophie zerstören, und die Poesie, um Raum zu gewinnen für die Religion und Moral, die du verkanntest: aber du hast nichts zerstören können als dich selber.
“Selected Ideas (1799-1800)”, Dialogue on Poetry and Literary Aphorisms, Ernst Behler and Roman Struc, trans. (1968) #90

The Bicycle Rider In Beverly Hills (1952)

Ibid., P.109.