“It is a good idea not to make up our minds prematurely on this issue. It is probably best not to let our personal preferences influence the decision. Rather, in the long tradition of successful science, we should permit nature to reveal the truth to us.”

Letter to John Tyndall (19 April 1851); letter 2411, edited by
Context: I have far more confidence in the one man who works mentally and bodily at a matter than in the six who merely talk about it — and I therefore hope and am fully persuaded that you are working. Nature is our kindest friend and best critic in experimental science if we only allow her intimations to fall unbiased on our minds. Nothing is so good as an experiment which, whilst it sets an error right, gives us (as a reward for our humility in being reproved) an absolute advancement in knowledge.

Source: Julian and Maddalo http://www.bartleby.com/139/shel115.html (1819), l. 170

Games for Actors and non-Actors (1992)
Context: In truth the Theatre of the Oppressed has no end, because everything which happens in it must extend into life…. The Theatre of the Oppressed is located precisely on the frontier between fiction and reality – and this border must be crossed. If the show starts in fiction, its objective is to become integrated into reality, into life. Now in 1992, when so many certainties have become so many doubts, when so many dreams have withered on exposure to sunlight, and so many hopes have become as many deceptions – now that we are living through times and situations of great perplexity, full of doubts and uncertainties, now more than ever I believe it is time for a theatre which, at its best, will ask the right questions at the right times. Let us be democratic and ask our audiences to tell us their desires, and let us show them alternatives. Let us hope that one day – please, not too far in the future – we’ll be able to convince or force our governments, our leaders, to do the same; to ask their audiences – us – what they should do, so as to make this world a place to live and be happy in – yes, it is possible – rather than just a vast market in which we sell our goods and our souls. Let’s hope. Let’s work for it!

Source: The People of the Wind (1973), Chapter 17 (p. 161)

"Literate Programming", The Computer Journal 27 (1984), p. 97. (Reprinted in Literate Programming, 1992, p. 99.)
Literate Programming (1984)

(Hudson Taylor’s Choice Sayings: A Compilation from His Writings and Addresses. London: China Inland Mission, n.d., 52).
Variant: Let us give up our work, our thoughts, our plans, ourselves, our lives, our loved ones, our influence, our all, right into His hand, and then, when we have given all over to Him, there will be nothing left for us to be troubled about, or to make trouble about.

Source: Lectures on the Will to Know (1970), p. 4

2009, Nobel Prize acceptance speech (December 2009)
Context: We do not have to think that human nature is perfect for us to still believe that the human condition can be perfected. We do not have to live in an idealized world to still reach for those ideals that will make it a better place. The non-violence practiced by men like Gandhi and King may not have been practical or possible in every circumstance, but the love that they preached — their fundamental faith in human progress — that must always be the North Star that guides us on our journey.
For if we lose that faith — if we dismiss it as silly or naïve; if we divorce it from the decisions that we make on issues of war and peace — then we lose what's best about humanity. We lose our sense of possibility. We lose our moral compass.
Like generations have before us, we must reject that future. As Dr. King said at this occasion so many years ago, "I refuse to accept despair as the final response to the ambiguities of history. I refuse to accept the idea that the 'isness' of man's present condition makes him morally incapable of reaching up for the eternal 'oughtness' that forever confronts him."
Let us reach for the world that ought to be — that spark of the divine that still stirs within each of our souls.

Source: A Woman's Thoughts About Women (1858), Ch. 8
Context: Let every one of us cultivate, in every word that issues from our mouth, absolute truth. I say cultivate, because to very few people — as may be noticed of most young children — does truth, this rigid, literal veracity, come by nature. To many, even who love it and prize it dearly in others, it comes only after the self-control, watchfulness, and bitter experience of years.