The possibility cannot be denied, but there are some considerations which render it improbable (apart from a catastrophe sweeping away European culture).  There are certain radical differences between the intellectual situation now and in antiquity.  The facts known to the Greeks about the nature of the physical universe were few.  Much that was taught was not proved.  Compare what they knew and what we know about astronomy and geography—­to take the two branches in which (besides mathematics) they made most progress.  When there were so few demonstrated facts to work upon, there was the widest room for speculation.  Now to suppress a number of rival theories in favour of one is a very different thing from suppressing whole systems of established facts.  If one school of astronomers holds that the earth goes round the sun, another that the sun goes round the earth, but neither is able to demonstrate its proposition, it is easy for an authority, which has coercive power,

[250] to suppress one of them successfully.  But once it is agreed by all astronomers that the earth goes round the sun, it is a hopeless task for any authority to compel men to accept a false view.  In short, because she is in possession of a vast mass of ascertained facts about the nature of the universe, reason holds a much stronger position now than at the time when Christian theology led her captive.  All these facts are her fortifications.  Again, it is difficult to see what can arrest the continuous progress of knowledge in the future.  In ancient times this progress depended on a few; nowadays, many nations take part in the work.  A general conviction of the importance of science prevails to-day, which did not prevail in Greece.  And the circumstance that the advance of material civilization depends on science is perhaps a practical guarantee that scientific research will not come to an abrupt halt.  In fact science is now a social institution, as much as religion.

But if science seems pretty safe, it is always possible that in countries where the scientific spirit is held in honour, nevertheless, serious restrictions may be laid on speculations touching social, political, and religious questions.  Russia has men of science inferior to none, and Russia has its notorious censorship.  It

[251] is by no means inconceivable that in lands where opinion is now free coercion might be introduced.  If a revolutionary social movement prevailed, led by men inspired by faith in formulas (like the men of the French Revolution) and resolved to impose their creed, experience shows that coercion would almost inevitably be resorted to.  Nevertheless, while it would be silly to suppose that attempts may not be made in the future to put back the clock, liberty is in a far more favourable position now than under the Roman Empire.  For at that time the social importance of freedom of opinion was not appreciated, whereas now, in consequence of the long conflict which