John Stuart Mill, On Liberty, Chapter II, “Of the Liberty of Thought and Discussion”:
[…] the peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.
When we consider either the history of opinion, or the ordinary conduct of human life, to what is it to be ascribed that the one and the other are no worse than they are? Not certainly to the inherent force of the human understanding; for, on any matter not self-evident, there are ninety-nine persons totally incapable of judging of it, for one who is capable; and the capacity of the hundredth person is only comparative; for the majority of the eminent men of every past generation held many opinions now known to be erroneous, and did or approved numerous things which no one will now justify. Why is it, then, that there is on the whole a preponderance among mankind of rational opinions and rational conduct? If there really is this preponderance—which there must be, unless human affairs are, and have always been, in an almost desperate state—it is owing to a quality of the human mind, the source of everything respectable in man, either as an intellectual or as a moral being, namely, that his errors are corrigible. He is capable of rectifying his mistakes by discussion and experience. Not by experience alone. There must be discussion, to show how experience is to be interpreted. Wrong opinions and practices gradually yield to fact and argument: but facts and arguments, to produce any effect on the mind, must be brought before it. Very few facts are able to tell their own story, without comments to bring out their meaning. The whole strength and value, then, of human judgment, depending on the one property, that it can be set right when it is wrong, reliance can be placed on it only when the means of setting it right are kept constantly at hand. In the case of any person whose judgment is really deserving of confidence, how has it become so? Because he has kept his mind open to criticism of his opinions and conduct. Because it has been his practice to listen to all that could be said against him; to profit by as much of it as was just, and expound to himself, and upon occasion to others, the fallacy of what was fallacious. Because he has felt, that the only way in which a human being can make some approach to knowing the whole of a subject, is by hearing what can be said about it by persons of every variety of opinion, and studying all modes in which it can be looked at by every character of mind. No wise man ever acquired his wisdom in any mode but this; nor is it in the nature of human intellect to become wise in any other manner. The steady habit of correcting and completing his own opinion by collating it with those of others, so far from causing doubt and hesitation in carrying it into practice, is the only stable foundation for a just reliance on it: for, being cognizant of all that can, at least obviously, be said against him, and having taken up his position against all gainsayers knowing that he has sought for objections and difficulties, instead of avoiding them, and has shut out no light which can be thrown upon the subject from any quarter—he has a right to think his judgment better than that of any person, or any multitude, who have not gone through a similar process.
As a model of discourse, compare William James on the “pretension” of possessing truth wholly; the portrayal of wisdom in Proverbs 8, here in the King James version:
1 Doth not wisdom cry? and understanding put forth her voice?
2 She standeth in the top of high places, by the way in the places of the paths.
3 She crieth at the gates, at the entry of the city, at the coming in at the doors.
4 Unto you, O men, I call; and my voice is to the sons of man.
5 O ye simple, understand wisdom: and, ye fools, be ye of an understanding heart.
6 Hear; for I will speak of excellent things; and the opening of my lips shall be right things.
7 For my mouth shall speak truth; and wickedness is an abomination to my lips.
8 All the words of my mouth are in righteousness; there is nothing froward or perverse in them.
9 They are all plain to him that understandeth, and right to them that find knowledge.
10 Receive my instruction, and not silver; and knowledge rather than choice gold.
11 For wisdom is better than rubies; and all the things that may be desired are not to be compared to it.
12 I wisdom dwell with prudence, and find out knowledge of witty inventions.
Mencken on “The Truth-Seeker,” in A Mencken Chrestomathy:
The man who boasts that he habitually tells the truth is simply a man who has no respect for it. It is not a thing to be thrown about loosely, like small change; it is something to be cherished and hoarded and disbursed only when absolutely necessary. The smallest atom of truth represents some man’s bitter toil and agony; for every ponderable chunk of it there is a brave truth-seeker’s grave upon some lonely ash-dump and a soul roasting in Hell.
The fundamental cause of trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.