In ergative verbs, if the verb does not assign a theta role to its subject ( because in the d-structure this position is empty ) then it also does not assign accusative case to its object ( because this position is empty in the s-structure, due to DP movement ).
42.
When applied to the sentence [ S [ NP Susan ] i gave [ NP the food ] j [ PP to Biff ] k ] the indices mark that " Susan " is assigned the external theta role of agent / source, " the food " is assigned the theme role, and " to Biff " is assigned the goal role.
43.
As a result, verbs which do not assign external theta roles will appear with subjects that are either dummy pronouns ( e . g . expletive " it, " " there " ), or ones which have been moved into subject position from a lower position ( e . g . subject of an embedded clause which comes after the verbs like seem, appear etc . ).
