How is inflectional morphology learned?

This article considers recent explanations of variability in the second language (L2) comprehension of inflectional morphology. The predictions of five accounts are spelled out: the emergentist account, the Feature Assembly Hypothesis, the Contextual Complexity Hypothesis, the Morphological Underspecification Hypothesis and the Combinatorial Variability Hypothesis. These predictions are checked against the results of an experimental study on the L2 acquisition of inflectional morphology (based on an extension of Slabakova and Gajdos 2008). English-native learners of German at beginning and intermediate proficiency levels took a multiple-choice test where they had to supply appropriate missing subjects. The predictions of the Morphological Underspecification Hypothesis and the Combinatorial Variability Hypothesis were largely supported by the experimental findings. It is argued that only accounts looking at mental representation of lexical features adequately explain L2 morphological variability.