This study addressess definitions of grammaticalization, (inter)subjectification and pragmaticalization in order to elucidate the relations between these terms. Grammaticalization is defined as a functionally motivated, complex language change type, (inter)subjectification as a particular kind of semantic change, and pragmaticalization as a grammaticalization subclass. This is illustrated by a review of the diachronic development of several German modal particles (such as aber, eben, ruhig).