Project B07 investigates medical registers of Galen of Pergamum in regard to formal and functional variation within the domains of evidentiality and epistemic modality. The role of both domains is in turn investigated within the higher-order category of stance-taking as a possible basis for their categorization. Based on a macro-modeling of medical discourse as a communicative domain in Imperial Age Greece, we determine contextual parameters that potentially interact with these linguistic features. Established text genres serve as a starting point for approaching variation in Galen but are not suitable as a structuring paradigm of these technical texts. They will thus be contrasted with the potential registers in order to reconceptualize the system of textual categorization.