What drives learner errors in written L2 production?

Accuracy in written L2 production can be influenced by many factors, including: (a) the relative similarity of the target structure to equivalent structure in the learner’s L1, and (b) the complexity of the target structure itself. The question of which of these two factors plays a stronger role is fundamental to theories of L2 acquisition. This written learner corpus study uses the English genitive alternation – s-genitives (‘the country's future’) and of-genitives (‘the future of the country’) – to attempt to shed light on this issue. L1 Spanish speakers lag behind L1 Japanese speakers in terms of accuracy rates when the target structure is an s-genitive. This L1 influence appears secondary to structural complexity effects; learners in both groups consistently use the simpler of-genitive with far higher accuracy. Both L1 and complexity effects are stronger in plural possessor contexts, with the plural feature apparently exacerbating learner difficulties with the s-genitive.