One of the earliest justifications for private property is contained in what has been called the occupation theory. This theory attempts to answer the relatively simple question of how things become the subject-matter of private ownership. It is taken for granted that things are ours because we have aquired them from another person who has ownership to pass on to us. Such acquisitions can occur through a voluntary transfer such as a gift or a bequest in a will or simply by a purchase for value. Thus the law prescribesmethods by which ownership can be acquired from another for example, a transfer by deed or mere delivery of the thing in question. The law does not , however, tell us how that chain of ownership began;in other words, why was ownership of the thing recognized in the first place?
Early philosophers such as Hugo Grotius and Pufendorf argued that the earth resources were given to mankind in common. Likewise, Blackstone wrote: "The Earth ... and all things therein are the general property of mankind, exclusive of other beings, from the immediate gift of the Creator ... all was in common among them, and that everyone took from the public stock to his own use such things as his immediate necessities required." In this sense of communal property, private property was born through individual taking, which Blackstone commented , was basically for his or her own need. If individuals will claim the material things of the earth thus effecting demand,such philosphers argued that the resulting scarcity value would naturally require a system of allocation in order to preserve peace and order.Without such a system there would be constant desputes as to what belonged to one person and what to another. The system which gave rise to the institution of private property was first occupation - hence, the occupation theory or jusification of private property.
The essence behind the occupation theory is that given that all material resources are given to mankind in common, such material resources become the private property of individuals through the consent of , or agreement with, the rest of mankind. The division of property takes place by reference to agreements. Such agreements can be express - that is a clear acceptance by a group of individuals that material resources (for example land or animals) - will be distributed amongst themselves on a mutual understanding. In the absence of such express agreements, an implied agreement could be found on a simple basis of first occupation. The basic principle emerging here is that the first occupation gives rise to private property; put into the eords of the common law, "possession is the roof of title."