D. 41,2,3,21: Titulierte Besitzarten, Erwerbsgründeund das unum genus possidendi
D. 41,2,3,21 turns on the issue of how possessio is to be divided. Understanding its content presupposes making a distinction that was self-evident for the Roman jurist but has never been made by later scholars of Roman law. They do not distinguish the varying ‘causes’ of possession (pro emptore … pro suo) which mark different types of lawful possession, and the ‘causes’ of acquisition (causae adquirendi) which justify obtaining possesion as by an owner. Taking a legally valid sale as an example the distinctive features of (possessio) pro emptore in contrast to emptio are established as well as their relevance for procedural practice. In particular there are no less than six forms of action in the law of inheritance for which these features are relevant. Next, the many negative effects of failing to make this distinction are indicated. There follows an in depth analysis and interpretation of the main phrases in Paul’s text: (i) quod nostrum non est; (ii) causae adquirendi, in particular iustae causae traditionis; (iii) unum genus possidendi; (iv) species infinitae.