The rule versus rote distinction is one of the most debated issues in recent psycholinguistics. Dual route accounts hold that words can either be stored whole in the mental lexicon or computationally derived by simple combinatorial rules such as stem+affix. Within this framework, response latencies in lexical decision tasks have been applied to point out the difference between rote memorization, on the one hand, and combinatorial rule manipulation, on the other. However, this paper argues that there may be alternatives to this distinction. It will be shown that German nouns, which can be distinctively marked for number, case or both number and case, do elicit differing reaction times. Crucially, this effect can neither be explained by surface frequency effects nor by internal morphological structure. Rather, it seems to be triggered by the degree of embedding into usage-based units.