Some people believe their “truths’ because they have faith in them. Others rely on hunches. Some rely on the authority of parents, teachers, or experts. None of these according to John Stuart Mill are solid grounds for action. This is what Mill says:

“There is the greatest difference between presuming an opinion to be true, because, with every opportunity for contesting it, it has not been refuted, and assuming its truth for the purpose of not permitting its refutation. Complete liberty of contradicting  and disproving our opinion is the very condition which justifies us in assuming its truth for the purpose of action; and on no other terms can a being with human faculties have any rational assurance of being right.”

It is for that reason that we don’t believe Putin is right when he says he was justified in invading Ukraine. Or we don’t believe the Ayatollah that Salman Rushdie should be killed? Or that gays are bound for hell because the Bible or the local preacher the says so.

Mill makes it clear that no opinions should be exempt from this process. He points out that there are some who urge that some principles are so certain that we should not be permitted to question them. But Mill disagrees. All opinions and all principles, even fundamental principles should be subject to challenge in this way. Only then can we really be certain. Or at least as close to certain as we can get. This is the result of living in an age that Mill says some call “destitute of faith, but terrified of scepticism in which people feel sure, not so much that their opinions are true, as that they should not know what to do without them—the claims of an opinion to be protected from public attack are rested not so much on its truth, as on its importance to society.” Of course, as Mill points out, this just shifts the problem, for it is just as important to have an infallible judge to determine which opinions are noxious or useful as to determine those that are true or false. In either case, the opinion must be allowed to be free to defend itself.

The real problem, Mill says, is not feeling sure of a doctrine, which he calls the assumption of infallibility, but rather the undertaking to decide this question for others, without allowing them to hear what can be said on the contrary side. This must be denounced no less when it is done to “protect” solemn convictions. All opinions must be free to defend themselves, even the sacred ones that are most important to us.

All truths should be subject to debate and argument. None are exempt. Not even sacred ones. That is what free speech means. All “truths” can be freely challenged.