When we say that ideas rule the world, or exercise a decisive power in history, we are generally thinking of those ideas which express human aims and depend for their realisation on the human will, such as liberty, toleration, equality of opportunity, socialism. Some of these have been partly realised, and there is no reason why any of them should not be fully realised, in a society or in the world, if it were the united purpose of a society or of the world to realise it. They are approved or condemned because they are held to be good or bad, not because they are true or false. But there is another order of ideas that play a great part in determining and directing the course of mans conduct but do not depend on his will—ideas which bear upon the mystery of life, such as Fate, Providence, or personal immortality. Such ideas may operate in important ways on the forms of social action, but they involve a question of fact and they are accepted or rejected not because they are believed to be useful or injurious, but because they are believed to be true or false. The idea of the progress of humanity is an idea of this kind, and it is important to be quite clear on the point. We now take it so much for granted, we are so conscious of constantly progressing in knowledge, arts, organising capacity, utilities of all sorts, that it is easy to look upon Progress as an aim, like liberty or a world-federation, which it only depends on our own efforts and good-will to achieve. But though all increases of power and knowledge depend on human effort, the idea of the Progress of humanity, from which all these particular progresses derive their value, raises a definite question of fact, which mans wishes or labours cannot affect any more than his wishes or labours can prolong life beyond the grave...