Classification of things

According to their physical nature or legal conditions, things could be classified in many different ways (see Gaius 2.1-18).

First, things could be owned privately, i.e., belong to some private individual (res in patrimonio; e.g., wine, a house), or they could be expressly excluded

Property law 145 from private ownership and all related legal transactions between private individuals (res extra patrimonium; e.g., air, rivers, the sea).

Second, in accord with the formalities required for the validity of a con­veyance, things could be considered res mancipi or res nec mancipi. The former were things relevant to households in an agricultural society. This category was limited to slaves, beasts of draught and burden (oxen, mules, and horses), the land of Italy (or provincial land with the status of Italic land), and rustic predial servitudes. Res mancipi could be conveyed only by a solemn and prescribed ritual form called mancipatio (from manu capere: to grasp with the hand), which required the presence of five Roman citizens as witnesses and of a man who held a scale. All other things were res nec mancipi. With the development of commerce, the importance of this distinction declined.

Third, things could be physical or intangible. Physical things could be touched (land, gold, clothes), while intangible things, of course, could not be (rights and obligations, for example). The distinction was important because, in general, only physical things could be possessed (possession required a physical holding), and only they could be acquired by informal conveyance (traditio) or usucaption (acquiring title to property by uninterrupted possession).

Fourth, things could be movable (res mobiles) or immovable (res immobiles). The distinction was relevant to categorizing theft (there could be no theft of immovable things), protecting possession, calculating the period required for usucaption, and even resolving questions of procedure. Movable property roughly corresponded to personal property, while immovable property corre­sponded to real property or real estate. Notably, the distinction between movable and immovable things never occupied in Roman law the importance that the distinction between real property and personal property came to have in the common law tradition.

Finally, there were fungible and nonfungible things. Fungibles were “those things that are estimated by weight, number, or measure, for instance, wine, oil, corn, coined money, copper, silver, or gold” (Inst. 3.14pr.). Nonfungible things were those identified and valued in and for themselves: e.g., a particular horse or piece of land or slave. The difference had legal relevance with respect to some legal relations, and specifically when it came to rules regarding risk: for such purposes, fungible things were completely interchangeable, since one instance was as good as another; not so for nonfungible things. In general, only nonfungible things could be used without being consumed. For this reason, there could be no usufruct of fungibles.