Grammars, parsers, and memory limitations

Linguistic competence cannot be adequately characterized by grammatical devices of finite state power. Nevertheless, there are reasons to suspect that the human parsing device cannot adequately deal with languages that fall outside this class. This paper discusses these issues, arguing that restrictions on available parsing memory, and on our ability to operate properly when parsing recursive constructions, mean that there is an interesting sense in which human parsing resources must be characterized as finite state. This means that certain constructions regarded as grammatical according to a (richer than finite state) competence grammar, are not parsable, or are parsed in a way which is not in exact correspondence to their description by this grammar. This raises the further question of how these constructions can nevertheless be understood appropriately, given the assumption that semantic interpretation relies on syntactic structure. The paper goes on to describe an implemented computer program which embodies the claims made here about the nature of human parsing. It produces semantic interpretations (logical forms) incrementally on a left to right pass through a sentence. It uses only finite state resources while parsing a context-free (or richer) type of grammar. Although using the information provided by a competence grammar it does not build any explicit syntactic representations. Its behaviour when parsing recursive constructions is claimed to closely approximate our own.