Sourced

• A foolish consistency is the hobgoblin of little minds, adored by little statesman and philosophers and divines. With consistency a great soul has simply nothing to do. He may as well concern himself with his shadow on the wall. Speak what you think now in hard words, and to-morrow speak what to-morrow thinks in hard words again, though it contradict every thing you said to-day. — 'Ah, so you shall be sure to be misunderstood.' — Is it so bad, then, to be misunderstood? Pythagoras was misunderstood, and Socrates, and Jesus, and Luther, and Copernicus, and Galileo, and Newton, and every pure and wise spirit that ever took flesh. To be great is to be misunderstood.
  • Ralph Waldo Emerson
  • Self Reliance (1841)

• Consistency is contrary to nature, contrary to life. The only completely consistent people are the dead.
  • Aldous Huxley
  • "Wordsworth in the Tropics" in Do What You Will (1929)

• Consistency is a virtue for trains: what we want from a philosopher is insights, whether he comes by them consistently or not.
  • Stephen Vizinczey
  • "Good Faith and Bad" in London Sunday Telegraph (4/21/1974)
  • reprinted in Truth and Lies in Literature (1986)

• Consistency is the last refuge of the unimaginative.
  • Oscar Wilde
  • "The Relation of Dress to Art" in Pall Mall Gazette (2/28/1885)
  • reprinted in Aristotle at Afternoon Tea:The Rare Oscar Wilde (1991)

• Consistency is the enemy of enterprise, just as symmetry is the enemy of art.
  • George Bernard Shaw
  • quoted by Michael Holroyd in Bernard Shaw: The Lure of Fantasy (1991)

• The test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function.
  • F. Scott Fitzgerald
  • "The Crack-Up" in Esquire (2/36)

• If a person never contradicts himself, it must be that he says nothing.
  • Miguel de Unamuno
  • quoted by Douglas R. Hofstadter in Godel, Escher, Bach (1979)

• Consistency requires you to be as ignorant today as you were a year ago.
  • Bernard Berenson
  • Notebook (1892)

• Of course I'm inconsistent! Only logicians and cretins are consistent!
  • Tom Robbins
  • Even Cowgirls Get The Blues (1976)
  • spoken by the character "The Chink"

• A silly ass ... wrote a paper to prove me inconsistent. ... Inconsistency is the bugbear of fools! I wouldn't give a damn for a fellow who couldn't change his mind with a change of conditions.
  • John Arbuthnot "Jacky" Fisher, British Admiral and First Sea Lord, in a letter to former Prime Minister Arthur Balfour (ndg)
  • source: Arthur J. Marder. From the Dreadnought to Scapa Flow: The Royal Navy in the Fisher Era, 1904-1919. (1961-1965)
  • quoted by Robert K. Massie in Deadnought: Britain, Germany and the Comiing of the Great War. (1991)

• I have forced myself to contradict myself in order to avoid conforming to my own tastes.
  • Marchel Duchamp
  • quoted by Harriet & Sidney Janis in "Marchel Duchamp: Anti-Artist" in View magazine (3/21/45)
  • reprinted in Robert Motherwell, Dada Painters and Poets (1951)

Unsourced

• The facts changed. Since the facts changed, I changed my position. What do you do, sir?
  • John Maynard Keynes (explaining why he changed his opinion on a particular economic issue)
  • widely cited as "When the facts change, I change my mind - what do you do, sir?", but since the source is unknown, it's also unknown which version, or the many others variations that exist, is correct.