John Stuart Mill makes the connection between free thought and free speech in his classic defense of speech, On Liberty (1859). The first chapter of Mill’s book is not called “Of free speech”, but rather “Of the liberty of thought and discussion”. That’s because speech for Mill is not an end in itself. It is rather one part of a broader freedom to find the truth that begins with a conscientious, trial-and-error attitude in which we are open to criticism and willing to learn from others and through experience. If we are beholden to prejudice, or hatred, or the pursuit of profit, or a desire to manipulate others, then our speech is constrained by these ulterior ends and not free.