It is clear that the most elementary condition, if thought is to be free, is the absence of legal penalties for the expression of opinions. No great country has yet reached to this level, although most of them think they have. The opinions which are still persecuted strike the majority as so monstrous and immoral that the general principle of toleration cannot be held to apply to them.

Legal penalties are, however, in the modern world, the least of the obstacles to freedom of thoughts. The two great obstacles are economic penalties and distortion of evidence. It is clear that thought is not free if the profession of certain opinions makes it impossible to earn a living. It is clear also that thought is not free if all the arguments on one side of a controversy are perpetually presented as attractively as possible, while the arguments on the other side can only be discovered by diligent search.