How the rights of private property are exercised necessarily differs from place to place and in different times. Nevertheless, the substance of private property, the right to control and to receive the fruits of ownership, cannot be altered. As Heinrich Rommen, one of Germany's premier jurists before escaping from the Nazis, explained in his book on the natural law,
"Thou shalt not steal" presupposes the institution of private property as pertaining to the natural law; but not, for example, the feudal property arrangements of the Middle Ages or the modern capitalist system. Since the natural law lays down general norms only, it is the function of the positive law to undertake the concrete, detailed regulation of real and personal property and to prescribe the formalities for conveyance of ownership. (Heinrich Rommen, The Natural Law, A Study in Legal and Social History and Philosophy. Indianapolis, Indiana: Liberty Fund, Inc., 1998, 59.)
Aristotle stressed the importance of the institution of private property many times in the Politics. While all the cites are far too numerous to quote, the following should give a good idea of the Philosopher's attitude towards private ownership of the means of production:
It is evident then that it is best to have property private, but to make the use of it common; but how the citizens are to be brought to it is the particular business of the legislator. And also with respect to pleasure, it is unspeakable how advantageous it is, that a man should think he has something which he may call his own; for it is by no means to no purpose, that each person should have an affection for himself, for that is natural, and yet to be a self-lover is justly censured; for we mean by that, not one that simply loves himself, but one that loves himself more than he ought; in like manner we blame a money-lover, and yet both money and self is what all men love. Besides, it is very pleasing to us to oblige and assist our friends and companions, as well as those whom we are connected with by the rights of hospitality; and this cannot be done without the establishment of private property, which cannot take place with those who make a city too much one; besides, they prevent every opportunity of exercising two principal virtues, modesty and liberality. Modesty with respect to the female sex, for this virtue requires you to abstain from her who is another's; liberality, which depends upon private property, for without that no one can appear liberal, or do any generous action; for liberality consists in imparting to others what is our own. (Aristotle, The Politics, II.v.)
One comment: Aristotle's statement that, "it is best to have property private, but to make the use of it common," has sometimes been construed as support for socialism. On the contrary, as we discover from the "laws and characteristics of social justice" discerned by William J. Ferree, S.M., Ph.D., making the use of property common has, in ordinary circumstances, been construed as an admonition not to use what you own to harm yourself, others, or the common good as a whole. You are, when possible, to employ your property and other rights in a way that strengthens the proper use of the institutions of the common good and their compliance with essential human nature. That is, we individually own and exercise control over the goods of the earth, but always with an eye toward the common good of all humanity (solidarity), both at the level closest to the individual (subsidiarity), and all other levels of the common good (social justice).