Suggested answer for Exercise 4

The verb cough in the sentence Sam coughed is an intransitive verb. Intransitive verbs take only one argument which is usually an agent. Since the specifier of the VP is the position of the theme argument according to the UTAH, this position is empty in this structure. The agent thematic role is assigned by the light verb to the specifier position of the vP. So the base position of the agent argument is in the specifier of the vP. Since this is no Case position, the DP has to move on to the specifier of the IP in order to receive Case from the finite I head. The thematic verb moves to the tense v and then frther on to I.