After reading it one feels that many of the more systematic books on politics by American university professors are useless, just because the writers dealt with abstract men, formed on assumptions of which they were unaware and which they had never tested either by experience or by study.
In the other sciences which deal with human actions, this division between the study of the thing done and the study of the being who does it is not found.

In criminology Beccaria and Bentham long ago showed how dangerous that jurisprudence was which separated the classification of crimes from the study of the criminal.

The conceptions of human nature which they held have been superseded by evolutionary psychology, but modern thinkers like Lombroso have brought the new psychology into the service of a new and fruitful criminology.
In pedagogy also, Locke, and Rousseau, and Herbart, and the many-sided Bentham, based their theories of education upon their conceptions of human nature.

Those conceptions were the same as those which underlay their political theories, and have been affected in the same way by modern knowledge.

For a short time it even looked, as if the lecturers in the English training colleges would make the same separation between the study of human institutions and human nature as has been made in politics.