Diachronic change and the nature of pronominal null subjects
This chapter focuses on the nature of null referential subjects (pro) through a case study in Russian. The loss of pro-drop in Middle Russian implied that: (i) null subjects (NSs) in non-embedded contexts became restricted to instances licensed by pragmatics. (ii) in embedded contexts, learners lost the possibility of parsing pro in the embedded subject gap, and started to parse the alternative null category available, PRO or trace. Afterwards, silent embedded subjects (both finite and non-finite) became licensed only by Obligatory Control. The unified way of licensing NSs in embedded contexts was determined by this diachronic process which confronted learners with two alternative elements to be parsed in the relevant gap, and had to imply some lexical or featural content for the referential pronoun (pro) as opposed to PRO or trace, contradicting views like the rich agreement hypothesis.