It pervaded the speculation of the age, and was formally deduced from the sensational psychology of Locke and Condillac.

It was developed, in an extreme form, in the work of Helvetius, De l'esprit (1758).
In this book, which was to exert a large influence in England, Helvetius sought, among other things, to show that the science of morals is equivalent to the science of legislation, and that in a well-organised society all men are capable of rising to the highest point of mental development.

Intellectual and moral inequalities between man and man arise entirely from differences in education and social circumstances.
Genius itself is not a gift of nature; the man of genius is a product of circumstances--social, not physical, for Helvetius rejects the influence of climate.

It follows that if you change education and social institutions you can change the character of men.
The error of Helvetius in ignoring the irremovable physical differences between individuals, the varieties of cerebral organisation, was at once pointed out by Diderot.

This error, however, was not essential to the general theory of the immeasurable power of social institutions over human character, and other thinkers did not fall into it.