What components of the grammar are responsible for controlling allomorphy, and under what conditions does one component exercise control in determining or selecting allomorphs?
How has the Indo-European language family changed and diversified over the millennia? What generalizations about language change generally can be drawn from this wealth of data?
How do the grammars for calculating word-level prominence (stress, accent, tone) function, what types of such grammars can exist, and how do they change diachronically?