 Mill’s argument for the freedom of thought and discussion is given in chapter 2 of On Liberty, and in it he aims to show that there should be no attempt “to control the expression of opinion” (Liberty, XVIII: 229; see Riley 2015: 74ff.). The chapter takes the form of a proof from the exhaustion of cases. Mill claims that, for any opinion P which is a candidate for suppression, P must be either: (i) true, (ii) false, or (iii) partially true. Whichever is the case, he argues, P’s assertion will be useful for discovering and maintaining the truth—and as such should be welcome. 