“…I will now motivate each of these principles in turn. First, (38a) is assumed (explicitly and implicitly) by a number of treatments, including Epstein et al 1998, Epstein 2000, Nunes & Uriagereka 2000, Larson 2015, Heck 2016, and Jayaseelan 2018, among others. The idea is, in effect, that because the Extension Condition forces merger to the root, derivation of {XP, YP} structures necessitates the existence of more than one workspace.…”