This paper deals with some theoretical aspects of how to write a contrastive grammar. Generally, non-diachronic comparative research on grammar can be divided into two subdisciplines: contrastive linguistics and general-comparative, i.e. typological linguistics. Although differing in perspective, method and research aims, both subdisciplines share the problem of how to define appropriate tertia comparationis. This paper discusses various angles from which a contrastive grammar can be organized and shows which tertia comparationis result from which of the different viewpoints. The specific effects on contrastive grammar writing are illustrated by contrasting some German and Estonian data. Finally, the paper argues for taking a functionalsemantic perspective for comparative grammar writing. One example of a functional-semantic oriented contrastive grammar is the project Grammatik des Deutschen im europäischen Vergleich based at the Institut für Deutsche Sprache (IDS), Mannheim. In conclusion, the paper presents a short overview on the outline of this project.
