In this article, we discuss passive se constructions in Romanian and Spanish. We argue that there is a projected implicit external argument in passive se constructions in both languages based on an available inalienable possession interpretation of body parts. These constructions, however, differ from each other in one important way: Romanian passive se allows a ‘by’-phrase, while Spanish passive se shows severe restrictions. Moreover, we illustrate that in Old Spanish, passive se freely allowed ‘by’-phrases. Thus, Modern Romanian reflects an earlier stage of Spanish. We propose a linguistic cycle to explain these differences, where Spanish and Romanian are at different stages of that cycle. The approach offers an explanation for a general pattern within Romance, where ‘by’-phrases are initially grammatical with passive se, but then become ungrammatical over time, a pattern to date that has not yet been explained. It also offers a thereotical account for why some languages do not develop passive se constructions.
