This paper reviews research on English past-tense acquisition to test the validity of the single mechanism model and the dual mechanism model, focusing on regular-irregular dissociation and semantic bias. Based on the review, it is suggested that in L1 acquisition, both regular and irregular verbs are governed by semantics; that is, early use of past tense forms are restricted to achievement verbs—regular or irregular. In contrast, some L2 acquisition studies show stronger semantic bias for regular past tense forms (e.g., Housen, 2002, Rohde, 1996). It is argued that L1 acquisition of the past-tense morphology can be accounted for more adequately by the single-mechanism model
