Date(s) - 11/10/2013
11:00 am - 12:00 pm
Limits of language can be studied from various perspectives such as morphology, syntax, and semantics, among others. At the syntactic level, one direction that has been pursued very actively is via the theory of formal languages, beginning with the so-called Chomsky hierarchy. In this hierarchy, the finite state languages (regular languages) and the context free languages (CFL) have been studied very extensively, leading to many important results relevant to syntax as well as parsing. At the same time, inadequacy of these two classes of grammars (languages) for capturing natural languages has been well documented by now.
A careful look at the pumping lemma for context free languages led to the discovery of the so-called tree adjoining grammars (TAG) and to the notion of mildly context sensitive languages (MCSL), which has served as a framework for showing equivalences among other systems (such as Combinatory Categorial Grammars, CCG and Head Grammars (HG), for example). This has led to a deeper understanding of the limits of language, more specifically, by trying to provide an answer to the question: how far do we need to be beyond CFL to achieve syntactic adequacy.
I will try to describe some of this recent work by a number of researchers in the past few years.