But how empty of true significance all these abstract formulas are! They do not merely restrict our conception of the evolution of private property when the thing itself is constantly changing; they also simplify it arbitrarily. For from age to age private property not only changes its meaning but also varies immensely in the matter of greater or less complexity. Sometimes it is applied to social relations that are extremely complex; again it seems to become more simplified. There are periods when human progress necessitates a complex notion of property; there are periods when it necessitates a simple one.
When slavery was changed to serfdom, property became more complex. The relations between master and slave were of a brutal simplicity. Then, in the Middle Ages, when the serf had a family and a patrimony, the master could not dispose of him so simply. The private property rights of the master in the serf are harder to define, less simple than the rights of the master in the slave. Human personality, which may be said to have been often non-existent in the slave and which was more evident in the serf, complicated the property relation; it introduced varied and uncertain elements into the conception of private property. And in this case, complexity certainly marks a step in advance. On the other hand, at the end of the eighteenth century, when the moment came for the middle classes and the peasants