Agreement Syncretisation and the Loss of Null Subjects : Quantificational Models for {Medieval French

This paper examines the nature of the dependency between the availability of null subjects and the ``richness'' of verbal subject agreement, known as Taraldsen's Generalisation (Adams, 1987; Rizzi, 1986; Roberts, 2014; Taraldsen, 1980). We present a corpus-based quantitative model of the syncretization of verbal subject agreement spanning the Medieval French period and evaluate two hypotheses relating agreement and null subjects: one relating the two as reflexes of the same grammatical property and a variational learning-based hypothesis whereby phonology-driven syncretization of agreement marking creates a learning bias against the null subject grammar. We show that only the latter approach has the potential to reconcile the intuition behind Taraldsen's Generalisation with the fact that it has proven nontrivial to formulate the notion of agreement richness in a way that would unequivocally predict whether a language has null subjects.