Does Japanese/German L1 Metrical and Tonal Structure Constrain the Acquisition of French L2 Morphology?

In different studies dedicated to the acquisition of verbal morphology by bilingual children or by L2 learners, it has been noted that differences in the acquisition process cannot be accounted for by only considering the distance between L1 and L2 morphology. Some forms, such as auxiliaries, may occur in L2 productions without being motivated by L1 morphology. To account for this, the prosodic transfer hypothesis—according to which the acquisition of morphology in the non-dominant language is influenced by the prosody of the dominant language—has been formulated. That prosodic features may influence the acquisition of morphology is interesting as it shows that the acquisition process must be apprehended by considering interfaces and interrelations between the various levels of linguistic description. The aim of this contribution is thus twofold: (i) clarifying to which aspects of prosody prosodic transfer hypothesis refers (specifically, among tonal and metrical prosodic elements, which one comes into play to account for morphological development); and (ii) explaining the importance of considering grammatical interfaces in study on L2 development. To do so, an exploratory study, which relies on the analysis of L2 French narratives produced by two learners with L1 Japanese and two with L1 German, was achieved. This preliminary analysis of the data suggests that metrical structure—more precisely, the nature of the basic metrical unit—may constrain the occurrence of auxiliary and vowel-final forms in the productions of Japanese learners.