The study examines German modal auxiliaries from the perspective of grammaticalization. The thrust is a dual one. First the attempt is undertaken to provide a systematic description of the coexistence of usages with differing degrees of grammaticalization in present-day German; second, a model is developed for the diachronic evolution of the more strongly grammaticalized usage of modal verbs as deictic facticity markers. Corpus analyses are drawn on both for the synchronic and the diachronic approaches.