The student of politics must therefore read history, and particularly the history of those events and habits of thought in the immediate past which are likely to influence the generation in which he will work.

But he must constantly be on his guard against the expectation that his reading will give him much power of accurate forecast.

Where history shows him that such and such an experiment has succeeded or failed he must always attempt to ascertain how far success or failure was due to facts of the human type, which he may assume to have persisted into his own time, and how far to facts of environment.

When he can show that failure was due to the ignoring of some fact of the type and can state definitely what that fact is, he will be able to attach a real meaning to the repeated and unheeded maxims by which the elder members of any generation warn the younger that their ideas are 'against human nature.' But if it is possible that the cause was one of mental environment, that is to say, of habit or tradition, or memory, he should be constantly on his guard against generalisations about national or racial 'character.' One of the most fertile sources of error in modern political thinking consists, indeed, in the ascription to collective habit of that comparative permanence which only belongs to biological inheritance.

A whole science can be based upon easy generalisations about Celts and Teutons, or about East and West, and the facts from which the generalisations are drawn may all disappear in a generation.