“Anyone who holds a true opinion without understanding is like a blind man on the right road.”
Plato, Republic, 506c
Plato, Republic
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Socrates 168
classical Greek Athenian philosopher -470–-399 BCRelated quotes

Source: "Jack Kemp, American Socialist" by Jeffrey Tucker, The Rothbard-Rockwell Report, September 1996, UNZ.org, 2016-05-22 http://www.unz.org/Pub/RothbardRockwellReport-1996sep-00001,

“The prejudiced and obstinate man does not so much hold opinions, as his opinions hold him.”
Source: A Dictionary of Thoughts, 1891, p. 438.

"The Importance of Critical Discussion" in On the Barricades: Religion and Free Inquiry in Conflict (1989) by Robert Basil
Context: There is an almost universal tendency, perhaps an inborn tendency, to suspect the good faith of a man who holds opinions that differ from our own opinions. … It obviously endangers the freedom and the objectivity of our discussion if we attack a person instead of attacking an opinion or, more precisely, a theory.

http://www.popmonk.com/actors/leonardo-dicaprio/quotes-leonardo-dicaprio.htm

The Fifth Modernization (1978) (excerpts)

Ma cos'è mai la storia, diceva spesso don Ferrante, senza la politica? Una guida che cammina, cammina, con nessuno dietro che impari la strada, e per conseguenza butta via i suoi passi; come la politica senza la storia è uno che cammina senza guida.
Variant translation:
"But," said he often, "what is history without politics? a guide who conducts without teaching any one the way; as politics without history, is a man without a guide to conduct him."
Richard Bentley translation (1834)
Source: The Betrothed (1827; 1842), Ch. 27, p. 374

“I hold that man is in the right who is most closely in league with the future.”
Letter to Georg Brandes (3 January 1882).