“The discovery of truth is prevented more effectively, not by the false appearance things present and which mislead into error, not directly by weakness of the reasoning powers, but by preconceived opinion, by prejudice.”

p, 125
The History of Oracles, and the Cheats of the Pagan Priests (1688)

The Great Infidels (1881)
Context: All the martyrs in the history of the world are not sufficient to establish the correctness of an opinion. Martyrdom, as a rule, establishes the sincerity of the martyr, — never the correctness of his thought. Things are true or false in themselves. Truth cannot be affected by opinions; it cannot be changed, established, or affected by martyrdom. An error cannot be believed sincerely enough to make it a truth.

Quoted in: Minteer, Catherine. "What We Observed in Teaching General Semantics." Et cetera 61 (2004): 482–86.
Context: Children must be free to think in all directions irrespective of the peculiar ideas of parents who often seal their children's minds with preconceived prejudices and false concepts of past generations. Unless we are very careful, very careful indeed, and very conscientious, there is still great danger that our children may turn out to be the same kind of people we are.

CVI.
Caelica (1633)

Source: The Great Seesaw: A New View of the Western World, 1750-2000 (1988)

Introductio ad prudentiam: Part II (1727), Gnomologia (1732)

"Religion: A Dialogue."
Variant translation: To free a man from error does not mean to take something from him, but to give him something.
Essays
Source: Essays and Aphorisms
Context: To free a man from error is to give, not to take away. Knowledge that a thing is false is a truth. Error always does harm; sooner or later it will bring mischief to the man who harbors it. Then give up deceiving people; confess ignorance of what you don't know, and leave everyone to form his own articles of faith for himself. Perhaps they won't turn out so bad, especially as they'll rub one another's corners down, and mutually rectify mistakes. The existence of many views will at any rate lay a foundation of tolerance. Those who possess knowledge and capacity may betake themselves to the study of philosophy, or even in their own persons carry the history of philosophy a step further.

“How divine scripture should be interpreted,” On First Principles, book 4, chapter 2, § 2, Readings in World Christian History (2013), p. 69
On First Principles
Context: The reason why all those we have mentioned hold false opinions and make impious or ignorant assertions about God appears to be nothing else but this, that scripture is not understood in its spiritual sense, but is interpreted according to the bare letter.

Craig v. Harney, 331 U.S. 367, 392 (1947).
Judicial opinions