Such is the drift of Mill’s main argument.  The present writer would prefer to state the justification of freedom of opinion in a somewhat different form, though in accordance with Mill’s reasoning.  The progress of civilization, if it is partly conditioned by circumstances beyond man’s control, depends more, and in an increasing measure, on things which are within his own power.  Prominent among these are the advancement of knowledge and the deliberate adaptation of his habits and institutions to new conditions.  To advance knowledge and to correct errors, unrestricted freedom of discussion is required.

[240] History shows that knowledge grew when speculation was perfectly free in Greece, and that in modern times, since restrictions on inquiry have been entirely removed, it has advanced with a velocity which would seem diabolical to the slaves of the mediaeval Church.  Then, it is obvious that in order to readjust social customs, institutions, and methods to new needs and circumstances, there must be unlimited freedom of canvassing and criticizing them, of expressing the most unpopular opinions, no matter how offensive to prevailing sentiment they may be.  If the history of civilization has any lesson to teach it is this:  there is one supreme condition of mental and moral progress which it is completely within the power of man himself to secure, and that is perfect liberty of thought and discussion.  The establishment of this liberty may be considered the most valuable achievement of modern civilization, and as a condition of social progress it should be deemed fundamental.  The considerations of permanent utility on which it rests must outweigh any calculations of present advantage which from time to time might be thought to demand its violation.

It is evident that this whole argument depends on the assumption that the progress of the race, its intellectual and moral development,

[241] is a reality and is valuable.  The argument will not appeal to any one who holds with Cardinal Newman that “our race’s progress and perfectibility is a dream, because revelation contradicts it”; and he may consistently subscribe to the same writer’s conviction that “it would be a gain to this country were it vastly more superstitious, more bigoted, more gloomy, more fierce in its religion, than at present it shows itself to be.”

While Mill was writing his brilliant Essay, which every one should read, the English Government of the day (1858) instituted prosecutions for the circulation of the doctrine that it is lawful to put tyrants to death, on the ground that the doctrine is immoral.  Fortunately the prosecutions were not persisted in.  Mill refers to the matter, and maintains that such a doctrine as tyrannicide (and, let us add, anarchy) does not form any exception to the rule that “there ought to exist the fullest liberty of professing and discussing, as a matter of ethical conviction, any doctrine, however immoral it may be considered.”