Abstract Choosing as my vantage point the linguistically motivated Müller-Sternefeld hierarchy (Müller and Sternefeld 2000), which classifies constraints according to their locality properties, I investigate the interplay of various syntactic constraint classes on a formal level. For non-comparative constraints, I use Rogers’ (2003) framework of multi-dimensional trees to state Müller and Sternefeld’s definitions in general yet rigorous terms that are compatible with a wide range of syntactic theories, and I formulate conditions under which distinct non-comparative constraints are equivalent. Comparative constraints, on the other hand, are shown to be best understood in terms of optimality systems (Frank and Satta 1998). From this I derive that some of them are reducible to non-comparative constraints.

The results jointly vindicate a broadly construed version of the Müller-Sternefeld hierarchy, yet they also support a refined picture of constraint interaction that has profound repercussions for both the study of locality phenomena in natural language and how the complexity of linguistic proposals is to be assessed.