In order more fully to illustrate the mischief of denying a hearing to opinions because we, in our own judgment, have condemned them, it will be desirable to fix down the discussion to a concrete case; and I choose, by preference, the cases which are least favourable to me – in which the argument against freedom of opinion, both on the score of truth and on that of utility, is considered the strongest. Let the opinions impugned be the belief in a God and in a future state, or any of the commonly received doctrines of morality. To fight the battle on such ground gives a great advantage to an unfair antagonist; since he will be sure to say (and many who have no desire to be unfair will say it internally), Are these the doctrines which you do not deem sufficiently certain to be taken under the protection of law? Is the belief in a God one of the opinions to feel sure of which you hold to be assuming infallibility? But I must be permitted to observe that it is not the feeling sure of a doctrine (be it what it may) which I call an assumption of infallibility. It is the undertaking to decide that question for others, without allowing them to hear what can be said on the contrary side. And I denounce and reprobate this pretension not the less if put forth on the side of my most solemn convictions. However positive anyone’s persuasion may be, not only of the falsity, but of the pernicious consequences – not only of the pernicious consequences, but (to adopt expressions which I altogether condemn) the immorality and impiety of an opinion; yet if, in pursuance of that private judgment, though backed by the public judgment of his country or his cotemporaries, he prevents the opinion from being heard in its defence, he assumes infallibility. And so far from the assumption being less objectionable or less dangerous because the opinion is called immoral or impious, this is the case of all others in which it is most fatal. These are exactly the occasions on which the men of one generation commit those dreadful mistakes which excite the astonishment and horror of posterity. It is among such that we find the instances memorable in history when the arm of the law has been employed to root out the best men and the noblest doctrines – with deplorable success as to the men, though some of the doctrines have survived to be (as if in mockery) invoked in defence of similar conduct towards those who dissent from them, or from their received interpretation.
Mankind can hardly be too often reminded, that there was once a man named Socrates, between whom and the legal authorities and public opinion of his time there took place a memorable collision. Born in an age and country abounding in individual greatness, this man has been handed down to us by those who best knew both him and the age as the most virtuous man in it; while we know him as the head and prototype of all subsequent teachers of virtue, the source equally of the lofty inspiration of Plato and the judicious utilitarianism of Aristotle, “i ma?stri di color che sanno,” the two headsprings of ethical as of all other philosophy. This acknowledged master of all the eminent thinkers who have since lived – whose fame, still growing after more than two thousand years, all but outweighs the whole remainder of the names which make his native city illustrious – was put to death by his countrymen, after a judicial conviction, for impiety and immorality. Impiety, in denying the gods recognised by the State; indeed, his accuser asserted (see the Apologia) that he believed in no gods at all. Immorality, in being, by his doctrines and instructions, a “corrupter of youth.” Of these charges the tribunal, there is every ground for believing, honestly found him guilty, and condemned the man who probably of all then born had deserved best of mankind to be put to death as a criminal.