This article outlines the typological variables that define or condition specific grammatical relations (GRs). It specifically discusses the relational roles and the referential properties of arguments. The article also reports the kinds of constructions that have GRs, and explores the interactions between GR definitions in different constructions. It then briefly addresses issues of worldwide distributions, and provides suggestions for future research. There is a common principle in the way referential features affect GR specifications. The properties of conjunction reduction are presented. The statistical evidence for referential hierarchy effects on case alignment is weak. GRs hold in constructions and not in languages. It is virtually impossible to estimate a priori which values on which variables will reveal significant clusters worldwide. The variables described in this article are meant to help in this work by providing a toolkit for comparing GRs across constructions in a single language, as well as across languages.