Executive Summary

J.S. Mill was an English philosopher noted for his works in philosophy, history, and politics. Chapter 2 of his 1859 On Liberty is a powerful attack on censorship in all forms and a passionate argument for objectivity and intellectual diversity in liberal education.

1. Individuals must be free to think for themselves: “If all mankind minus one, were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person, than he, if he had the power, would be justified in silencing mankind.”
2. On complicated matters especially, discussion and debate are essential tools of truth-seeking, as one can have more confidence in opinions that can survive those contesting processes: "Complete liberty of contradicting and disproving our opinion, is the very condition which justifies us in assuming its truth for purposes of action".
3. Consequently, a person can believe an opinion more strongly or think himself expert only to the extent 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.” Then “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.”
4. In training a young mind about any complicated matter, it is not enough to state a series of truths to be memorized, nor even merely the truths plus the grounds for them. One must also expose the student to the contrary opinions and the arguments for them.  “He who knows only his own side of the case, knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side; if he does not so much as know what they are, he has no ground for preferring either opinion.”
5. Mill argues further that educational institutions should hire teachers of diverse opinions because the student “must be able to hear them from persons who actually believe them; who defend them in earnest, and do their very utmost for them. He must know them in their most plausible and persuasive form.”
6. Schools and universities, therefore, with uniformity of opinion among the teachers and professors do themselves and their students a disservice, as they become intellectually complacent and merely perpetuate the combination of truths, half-truths, and falsehoods they happen to believe. “Both teachers and learners go to sleep at their post, as soon as there is no enemy in the field.”
7. These objective habits of mind are essential for assessing and re-assessing past and current ideas, as well as for generating and evaluating new ideas to make progress on complicated matters in science, politics, philosophy, and other intellectual fields.

Read Chapters 1 and 2 of J.S. Mill’s On Liberty here. The full text is here. Summary by Stephen Hicks, 2020.