Over the past few decades there has been a lot of debate about language learning and the opinion about the status of mental rule during the process of language learning is still divided between different researches. The present study examines learning morphology of German noun plurals based on rules, examples or on both, rules and examples. The results across these three experimental conditions suggest that the morphological patterns are learned more easily in the form of rules and thus, seem to be more easily captured by dual-route (which suggest that rules and exceptions are processed by two qualitatively different mechanisms) than single route theories (which suggest a singe mechanism for processing both rules and exceptions). However, a closer examination of error patterns across the five rules (-e, -n, -er, ?, -s) revealed results confronting dual-route theories and suggest the existence of two rulemechanisms (-n and -s) rather than one for learning regular inflection in German plural nouns. Moreover, the second rule (with plural ending -n) was the easiest one to be learned, although it is the fifth rule (with plural ending -s) which is considered as a default rule in German.