“When we know clearly, then should we discuss:
To guess is one thing, and to know another.”

The Thirteenth Revelation, Chapter 34
Context: Our Lord God shewed two manner of secret things. One is this great Secret with all the privy points that belong thereto: and these secret things He willeth we should know hid until the time that He will clearly shew them to us. The other are the secret things that He willeth to make open and known to us; for He would have us understand that it is His will that we should know them. They are secrets to us not only for that He willeth that they be secrets to us, but they are secrets to us for our blindness and our ignorance; and thereof He hath great ruth, and therefore He will Himself make them more open to us, whereby we may know Him and love Him and cleave to Him. For all that is speedful for us to learn and to know, full courteously will our Lord shew us.

The Language of Love.
Song lyrics, Windows and Walls (1984)

Source: More Than You Know

Source: The Hunger Games

Source: Changes

Source: The Gendered Atom: Reflections on the Sexual Psychology of Science (1999), Ch.7 The Rape of Nature

We know to tell many fictions like to truths, and we know, when we will, to speak what is true.
We know how to tell many lies that pass for truth, and we know, when we wish, to tell the truth itself.
Source: The Theogony (c. 700 BC), lines 27–28. Variant translations:

remarks (2 May 1956) at a Caltech YMCA lunch forum http://calteches.library.caltech.edu/49/2/Religion.htm
Context: In this age of specialization men who thoroughly know one field are often incompetent to discuss another. The great problems of the relations between one and another aspect of human activity have for this reason been discussed less and less in public. When we look at the past great debates on these subjects we feel jealous of those times, for we should have liked the excitement of such argument. The old problems, such as the relation of science and religion, are still with us, and I believe present as difficult dilemmas as ever, but they are not often publicly discussed because of the limitations of specialization.

Department of Defense news briefing (12 February 2002)
Variant:
Now what is the message there? The message is that there are no "knowns." There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know. So when we do the best we can and we pull all this information together, and we then say well that's basically what we see as the situation, that is really only the known knowns and the known unknowns. And each year, we discover a few more of those unknown unknowns.
:It sounds like a riddle. It isn't a riddle. It is a very serious, important matter.
:There's another way to phrase that and that is that the absence of evidence is not evidence of absence. It is basically saying the same thing in a different way. Simply because you do not have evidence that something exists does not mean that you have evidence that it doesn't exist. And yet almost always, when we make our threat assessments, when we look at the world, we end up basing it on the first two pieces of that puzzle, rather than all three.
:* Extending on his earlier comments in a press conference at NATO Headquarters, Brussels, Belgium (6 June 2002) http://www.nato.int/docu/speech/2002/s020606g.htm
2000s