is as incumbent on them to prohibit the
circulation of pernicious opinions as to prohibit any anti-social
actions. They can argue that a man may do far more harm by propagating
anti-social doctrines than by stealing his neighbour's horse or making
love to his neighbour's wife. They are responsible for the welfare of
the State, and if they are convinced that an opinion is dangerous, by
menacing the political, religious, or moral assumptions on which the
society is based, it is their duty to protect society against it, as
against any other danger.

[14]

The true answer to this argument for limiting freedom of thought will
appear in due course. It was far from obvious. A long time was needed to
arrive at the conclusion that coercion of opinion is a mistake, and only
a part of the world is yet convinced. That conclusion, so far as I can
judge, is the most important ever reached by men. It was the issue of a
continuous struggle between authority and reason--the subject of this
volume. The word authority requires some comment.

If you ask somebody how he knows something, he may say, "I have it on
good authority," or, "I read it in a book," or, "It is a matter of
common knowledge," or, "I learned it at school." Any of these replies
means that he has accepted information from others, trusting in their
knowledge, without verifying their statements or thinking the matter out
for himself. And the greater part of most men's knowledge and beliefs is
of this kind, taken without verification from their parents, teachers,
acquaintances, books, newspapers. When an English boy learns French, he
takes the conjugations and the meanings of the words on the authority of
his teacher or his grammar. The fact that in a certain place, marked on
the map, there is a populous city called Calcutta, is for most

[15] people a fact accepted on authority. So is the existence of
Napoleon or Julius Caesar. Familiar astronomical facts are known only in
the same way, except by those who have studied astronomy. It is obvious
that every one's knowledge would be very limited indeed, if we were not
justified in accepting facts on the authority of others.

But we are justified only under one condition. The facts which we can
safely accept must be capable of demonstration or verification. The
examples I have given belong to this class. The boy can verify when he
goes to France or is able to read a French book that the facts which he
took on authority are