“Without contraries there is no progression.”

Source: The Blind Watchmaker (1986), Chapter 7 “Constructive Evolution” (p. 178)

Source: Wooden: A Lifetime of Observations and Reflections On and Off the Court

Inward Bound : Of Matter and Forces in the Physical World (1988) http://books.google.com/books?id=mREnwpAqz-YC, p. 4
Context: Progress leads to confusion leads to progress and on and on without respite. Every one of the many major advances … created sooner or later, more often sooner, new problems. These confusions, never twice the same, are not to be deplored. Rather, those who participate experience them as a privilege.

No habrá desarrollo sin educación, ni progreso sin cultura.
Instituto Experimental del Atlántico "José Celestino Mutis" http://web.archive.org/web/20130421041951/http://www.colegio-iea.com/Glosas%20Experimentales_Nr1.pdf

2014, 25th Anniversary of Polish Freedom Day Speech (June 2014)

Zen Masters : The Wisdom of Frank Zappa (2003)

Remarks by President Obama and Prime Minister Abe of Japan at Hiroshima Peace Memorial at Hiroshima Peace Memorial in Hiroshima, Japan (May 27, 2016) https://www.whitehouse.gov/the-press-office/2016/05/27/remarks-president-obama-and-prime-minister-abe-japan-hiroshima-peace
2016
Context: There are many sites around the world that chronicle this war -- memorials that tell stories of courage and heroism; graves and empty camps that echo of unspeakable depravity. Yet in the image of a mushroom cloud that rose into these skies, we are most starkly reminded of humanity’s core contradiction; how the very spark that marks us as a species -- our thoughts, our imagination, our language, our tool-making, our ability to set ourselves apart from nature and bend it to our will -- those very things also give us the capacity for unmatched destruction. [... ] Science allows us to communicate across the seas and fly above the clouds; to cure disease and understand the cosmos. But those same discoveries can be turned into ever-more efficient killing machines. The wars of the modern age teach this truth. Hiroshima teaches this truth. Technological progress without an equivalent progress in human institutions can doom us. The scientific revolution that led to the splitting of an atom requires a moral revolution, as well.

Source: Love, Poverty, and War: Journeys and Essays

Heretics and Heresies (1874)
Context: Every church pretends that it has a revelation from God, and that this revelation must be given to the people through the church; that the church acts through its priests, and that ordinary mortals must be content with a revelation — not from God — but from the church. Had the people submitted to this preposterous claim, of course there could have been but one church, and that church never could have advanced. It might have retrograded, because it is not necessary to think or investigate in order to forget. Without heresy there could have been no progress.