Ulpian is regarded as one of the most influential jurists of the Roman classical period. At the center of Nils Humrich’s doctoral project are Books 17 and 18 of his ad Sabinum commentary, which deal with the legal concept of usufruct. The aim of the study is a systematic analysis of the textual structure. In particular, it seeks to determine the extent to which Ulpian develops an independent line of legal reasoning (autonomy), or whether he adheres closely to a pre-existing interpretative framework (heteronomy) based on the work of Massurius Sabinus, the libri tres iuris civilis, which survives only indirectly. Since neither Ulpian’s commentary nor Sabinus’ original work has been preserved in its entirety and is transmitted only through later sources such as the Corpus Iuris Civilis and the Fragmenta Vaticana, the project relies on Otto Lenel’s reconstruction in the Palingenesia Iuris Civilis. Against this background, the study adopts a systematically structured methodological approach.

The first phase involves the collection and thematic classification of the reconstructed text. On this basis, the material is analyzed within its legal-historical context in order to uncover Ulpian’s argumentative structure, his doctrinal method, and the internal organization of his presentation. Special attention is given to the integration of the legal principles and case examples into their dogmatic-historical framework, with the aim of identifying continuities and lines of development within classical Roman private law. In the final phase, the findings are critically compared with the current state of research and reflected upon accordingly.