Occasionally in "On Liberty," Mill leans heavily into figurative language in order to make his point, although most of his work is relatively plain and unadorned. This passage, from Chapter 2, is one notable exception, in which Mill uses similes and metaphors of light, fire, and nature to emphasize how powerful truths eventually escape even the harshest persecution:
Socrates was put to death, but the Socratic philosophy rose like the sun in heaven, and spread its illumination over the whole intellectual firmament. Christians were cast to the lions, but the Christian church grew up a stately and spreading tree, overtopping the older and less vigorous growths, and stifling them by its shade. Our merely social intolerance kills no one, roots out no opinions, but induces men to disguise them, or to abstain from any active effort for their diffusion.
Though Socrates died, his philosophy lived on with such power, Mill contends, that has shone through ages like the glare of the sun. Christians, for their part, may have been persecuted—and Jesus himself may have been executed—but the metaphorical tree that is Christianity could not be felled. Instead, by Mill's metaphor, this tree grew until it blocked out other religions like a large tree blocks out the sun from other smaller trees in its shade.
Later in this same section, Mill continues to use the figurative language of fire:
With us, heretical opinions do not perceptibly gain, or even lose, ground in each decade or generation; they never blaze out far and wide, but continue to smoulder in the narrow circles of thinking and studious persons among whom they originate, without ever lighting up the general affairs of mankind with either a true or a deceptive light.
Though these "heretical" ideas may not conjure the celestial inferno that Socrates's philosophy has, they nonetheless prove to be durable. Like smoldering coals in a fireplace, they persist, although they do not break into the mainstream.
These passages are vital examples of Mill's exploration of how humanity's ideas take root and spread in the face of attempts at censorship by church, state, or social tyranny. Progress—even the progression of heresy—will always burn on, but it can nonetheless be hindered if authority tries to "smother" it out. New, challenging ideas, Mill argues, must always be entertained.
