Of the Liberty of Thought and Discussion

Mill defends free expression on four distinct grounds, and he wants all four to bear weight. First: the silenced opinion may be true. To suppress it is to assume our own infallibility, and history is the long record of how badly that assumption ages — Socrates condemned by Athens, the early Christians persecuted by Marcus Aurelius, Galileo forced to recant. The assumption of infallibility is no less dangerous because the majority holds it.

Second: even if the suppressed opinion is false, it may contain a portion of truth. Prevailing opinion is rarely the whole truth; it is only by the collision of ideas that the remainder is made up. Third: an opinion that is true but never contested decays into prejudice — held by rote, without grasp of its grounds, defenceless against intelligent attack. The meaning of a doctrine fades when it is not continuously defended; it becomes a formula, recited without force on conduct.

Fourth: the living force of a true belief depends on the struggle to hold it. A person who has never had to defend a conviction does not really possess it. Mill is careful to note that this is not an argument for permanent uncertainty: it is an argument for the discipline of intellectual contest. The four arguments together make free discussion not a polite ornament of liberal society but the working machinery by which any society capable of correcting itself stays so.