The writer must earn money in order to be able to live and to write, but he must by no means live and write for the purpose of making money.
Nothing can have value without being an object of utility.
The ruling ideas of each age have ever been the ideas of its ruling class.
Revolutions are the locomotives of history.
The production of too many useful things results in too many useless people.
The history of all previous societies has been the history of class struggles.