The acquisition of ownership in Roman law took various forms.

These form the body of 0.41.1. At the outset a distinction lias to be drawn between acquiring own­ership inter vivos and through succession, i.e. inheritance on death. Inheritance will be the subject of Chapter 8.

The methods of acquiring ownership inter vivos can be classified in a number of ways. For example, some methods can be described in modern civilian systems as 'original'—where the acquisition of ownership did not depend on there being a prior owner—whereas others were derivative, i.e. where ownership was derived from a prior owner (see Metzger, Companion, 49-65). Or some methods were formal, others causal: in the former case ownership passed because of the use of particular form and ceremony, whereas in the latter case ownership depended on the ground or 'cause' of the acquisition. In Roman law, however, Gaius described the primary classification as follows:

Gaius, Common Mutters or (iohlen Things, book 2: Of some things we acquire ownership under the law of nations which is observed, by natural reason, among all men generally, of others under the civil law which is peculiar to our city. And since the law of nations is the older, being the product of human nature itself, it is necessary to treat of it first. (D.41.1.1 pr.)

Justinian followed this basic distinction between ins civile and ins gentium modes of acquisition. The importance of the distinction lay in the fact that the ins civ­ile modes were confined to those with commercium, i.e. mainly Roman citizens, whereas the ins gentium methods applied to acquisition of property by citizens and non-citizens alike (cf. Inst.2.1.1.; Inst.Gai.2.65.). The ius civile modes were mancipatio, cessio in hire, usucapio, and ad'mdicatio. The ius gentium modes were occupatio, accessio, specificatio, the acquisition of ownership of fruits, treasure­trove, and traditio.

The classification of the modes of acquisition of ownership into original and deriv­ative is based on a modern interpretation of Roman law texts and it is the preferred classification in modern civilian systems. It looks rather different. Thus, the deriva­tive modes of acquisition of ownership are mancipatio, cessio hi hire, and traditio. The original modes of acquisition of ownership are usucapio, occupatio, accessio, specifi­catio, the severance and gathering of fruits, as well as treasure trove. Note that the modern classification (original and derivative) cuts across the Roman categories and leaves certain issues unresolved (see the acquisition of ownership of property through gifts at the end of this chapter). To reinforce the use of this modern classification in civilian systems, let us follow this example by starting with the derivative modes of acquisition.

7.1