According to Bybee (1985, 1994), the relevance of one linguistic sign to another determines its formal expression as either lexical, morphological or syntactic. Highly relevant categories are predicted to be situated closer to the lexical root, i. e. by inflectional or derivational expression, whereas less relevant categories are more likely to be expressed periphrastically or syntactically. Nübling/Dammel (2004) show that relevance plays an important role in the diachronic reorganization of verbal inflection in German. We propose that this also applies to the diachronic development of the nominal categories in German, which is characterized by two major principles: levelling of caseforms versus maintenance and (even) strengthening of the more relevant number category. However, relevance is not the only principle shaping the diachronic reorganization of nominal inflection. We argue that a low degree of grammaticalization may counteract relevance as it usually correlates with low syntagmatic cohesion and high semantic specificity. Furthermore, we show that typological properties may interfere with the relevance criterion: The periphrastic expression of the relevant category of definiteness within the DP satisfies the overall tendency of German to express grammatical categories discontinuously through framing constructions (›Klammerprinzip‹). Another exception is the ›weak masculine declension‹ which contains mainly nouns denoting highly animate referents. We propose that animacy may alter the relevance hierarchy in the sense that demarcation of thematic roles (agent vs. others) through case marking is more important for highly animate referents than number marking.