a) Topics and Objectives: Dialectical topoi constitute an essential component of Aristotelian logic and theory of argumentation (dialectics). These can be characterized as essential patterns of argumentation which allow us to found premises which are suited to the establishment of specific theses. Our research group concentrates on two themes: the first working focus consists of a precise investigation of the topos-based dialectical logic found in Aristotle. We are concerned in particular with the dialectical texts contained in the Organon (Topics, Rhetoric, Sophistical Refutations), and we are considering their relationship to the formal logic developed in the Prior Analytics. The second focus of our work is an investigation of the reception of Aristotelian dialectics in the Renaissance. Occurring in the 16th century was in intensive reception of the Aristotelian Topics, as suggested by numerous new translations and commentaries. We are concentrating on the relationship between veritas/scientia and opinio/probabilitas in the epistemology of the Renaissance. In particular, we are interested in the question of how the dialectics and rhetoric of the Renaissance were influenced by the form and genre of the dialogue, and in the role played in the Renaissance by the spatial dimension, which is contained both in Aristotle’s definition of the topos as the »place from which the attack comes«, as well as in Cicero’s definition of the locus as the »seat of the argument« (sedes argumentorum). b) Methods: Relevant passages from the texts of the Aristotelian Organon are analyzed and set into relationship with one another. Consulted in particular in interpreting these texts is the inventory of 20th century theories dealing with logic and argumentation; modern mereological and topological systems, for example, are used in reconstructing Aristotelian logic, albeit without overlooking the historical specificity of the problems that are bound up with these antique texts. c) State of the Discussion: The group has concluded that Aristotelian formal logic is dependent upon and was shaped in various ways by topos-based dialectical logic. Aristotelian predication theory, for example, plays a decisive role for various aspects of the Aristotelian syllogistic which is contained in the Prior Analytics. Beyond this, the group has demonstrated that interpretations of the Aristotelian Topics made an essential contribution to the emergence of a relativistic epistemology in the Renaissance. The status of opinio/probabilitas in the Renaissance, for example, was influenced by interpretations of the Aristotelian concept of endoxon.