VP-ellipsis in control infinitives

It has been observed that VP-ellipsis is possible not only in finite clauses but also in control infinitives, which suggests that even nontensed T enters into an Agree relation. However, the matter is not this simple: VP-ellipsis is possible in the Obligatory Control (OC) context (i.e., in a complement infinitive)，but not in the Non-Obligatory Control (NOC) context. Thus, the questions to solve are: What is responsible for VP-ellipsis in infinitives and what differentiates OC infinitives from NOC infinitives.I first show the correlation between the interpretation of PRO and the possibility of VP-ellipsis and provide an analysis where PRO is identified by the φ-features' specification through T， which is possible only in OC infinitives. I further argue that this feature specification is sensitive to Subjacency and suggest that movement would be involved only in OC infinitives.