In so-called pro-drop or 'null-subject' languages, such as Italian, a pronominal subject may be phonetically null in tensed sentences. It is generally assumed that in such cases, the subject is the element pro, and that this pro is licensed by the verbal inflection ( INFL).
- Jaeglli, O. and K. Safir (eds.) 1989. The Null Subject Parameter, Kluwer Academic Press: Amsterdam.
- Rizzi, L. 1982. Issues in Italian syntax, Foris, Dordrecht