Pronouns without explicit noun phrase antecedents pose a problem for any theory of reference resolution. We report here on an empirical study of such pronouns in the Santa Barbara Corpus of Spoken American English, a corpus of spontaneous, casual conversation. In this paper we focus on some problematic subclasses of pronouns which could be analyzed as either referring to entities of various degrees of abstractness that were introduced by or implied in previous discourse, or as non-referential, including pleonastic.
Gundel, Jeanette, Nancy Hedberg, and Ron Zacharski. 2005. Pronouns without NP Antecedents: How do we know when a pronoun is referential. Anaphora Processing: Linguistic, Cognitive and Computational Modelling, ed. by Antonio Branco, Tony McEnery, and Ruslan Mitkov. John Benjamins, 351-364. (pdf)