“Theory confronts experiment, and both sides are a mixture of obscurity and clarity.”

Source: Thought Without a Body? (1994)
Perigrenations Law Form

Source: The Story of the Lost Child

“The Obscurity of the Poet”, p. 4
Poetry and the Age (1953)

Third Annual Message to Congress (6 December 1887), discussing tariffs. Compare "Free trade is not a principle, it is an expedient", Benjamin Disraeli, On Import Duties, April 25, 1843.
Context: Both of the great political parties now represented in the Government have by repeated and authoritative declarations condemned the condition of our laws which permit the collection from the people of unnecessary revenue, and have in the most solemn manner promised its correction; and neither as citizens nor partisans are our countrymen in a mood to condone the deliberate violation of these pledges.
Our progress toward a wise conclusion will not be improved by dwelling upon the theories of protection and free trade. This savors too much of bandying epithets. It is a condition which confronts us — not a theory. Relief from this condition may involve a slight reduction of the advantages which we award our home productions, but the entire withdrawal of such advantages should not be contemplated. The question of free trade is absolutely irrelevant, and the persistent claim made in certain quarters that all the efforts to relieve the people from unjust and unnecessary taxation are schemes of so-called free traders is mischievous and far removed from any consideration for the public good.

the conclusion of the historical Stern-Gerlach experiment, in The Method of Molecular Rays http://nobelprize.org/nobel_prizes/physics/laureates/1943/stern-lecture.html, Nobel Lecture, December 12, 1946.

1960s, Freedom From The Known (1969)
Context: We human beings are what we have been for millions of years — colossally greedy, envious, aggressive, jealous, anxious and despairing, with occasional flashes of joy and affection. We are a strange mixture of hate, fear and gentleness; we are both violence and peace.

Small Houses: Their Economic Design and Construction (1922)
Context: Clarity or Decision.... without it there is uncertainty, hesitation, obscurity, instability... incomparable with good art. The meaning and object of the design should be clear... it should be frank, as the French say.

Source: A Treatise On Political Economy (Fourth Edition) (1832), Book II, On Distribution, Chapter VIII, Section I, p. 354