Towards the end of his career, together with graduate students at Stanford, Sag turned his attention to developing a clearer understanding of the roles of processing and grammar in determining (un)acceptability.
he argued that the unacceptability associated with phenomena such as "island constraints" derives not from ungrammaticality but in fact from more general processing pressures (Staum and Sag 2008;Hofmeister and Sag 2010;Staum Casasanto, Hofmeister, and Sag 2010;Hofmeister et al.