The practice of reducing GFs to constituency relations between phrase markers dates back to Chomsky's dissertation (Chomsky, 1955), and was described in some detail in Chomsky (1965). Chomsky's account consists in identifying structural relations of dominance such as `[NP,S]' and `[NP,VP]' which define thematic GRs at D-structure, and secondary (i.e. non-thematic) GRs at S-structure. Secondary GRs result from movement operations at S-structure induced by the case filter. Thematic GRs are derived from the categorial rules which generate D-structure phrase markers and specify the structural environment in which an argument is assigned a particular role by a predicate, according to the predicate's inherent lexical properties. The realisation of lexical properties is secured through the Projection Principle.