It is passing strange that our philosophers of the Revolutionary period should have formed their conception of a free society by reference to societies where everyone was not free - where, in fact, the vast majority were not free. It is no less strange that they never stopped to ask whether perhaps the characters which they so much admired were not made possible by the existence of a class which was not free. Rousseau, in whose philosophy were many things, was fully conscious of this difficulty: "Must we say that liberty is possible only on a basis of slavery? Perhaps we must.