In this paper we apply MOSAIC (Model of Syntax Acquisition in Children) to the simulation of the developmental patterning of children’s Optional Infinitive (OI) errors in four languages: English, Dutch, German and Spanish. MOSAIC, which has already simulated this phenomenon in Dutch and English, now implements a learning mechanism that better reflects the theoretical assumptions underlying it, as well as a chunking mechanism which results in frequent phrases being treated as one unit. Using one, identical model that learns from child-directed speech, we obtain a close quantitative fit to the data from all four languages, despite there being considerable cross-linguistic and developmental variation in the OI phenomenon. MOSAIC successfully simulates the difference between Spanish (a pro-drop language where OI errors are virtually absent), and Obligatory Subject languages that do display the OI phenomenon. It also highlights differences in the OI phenomenon across German and Dutch, two closely related languages whose grammar is virtually identical with respect to the relation between finiteness and verb placement. Taken together, these results suggest that (a) cross-linguistic differences in the rates at which children produce Optional Infinitives are graded, quantitative differences that closely reflect the statistical properties of the input they are exposed to and (b) theories of syntax acquisition need to consider more closely the role of input characteristics as determinants of quantitative differences in the cross-linguistic patterning of phenomena in language acquisition
