The Natural Language Conjunction 'and'

In the first part of this article, we show that, contrary to the Gricean tradition, inter-clausal "and" is not semantically equivalent to logical conjunction and, contrary to temporal approaches such as Bar-Lev and Palacas 1980, it is not temporally loaded. We then explore a commonsense idea - namely that while sentence juxtaposition might be interpreted either as discourse coordination or subordination, "and" indicates coordination. SDRT already includes notions of coordinating and subordinating discourse relations (cf. Lascarides and Asher 1993, Asher 1993), and the meaning of "and" is related to this distinction. Similar distinctions that play a crucial role in anaphora resolution have also appeared in AI - cf. Scha and Polanyi 1988, or Webber 1991. However, this discourse-structure-based distinction has not been well defined yet, and our approach provides independent motivation for it. This paper argues that the semantics of "and" includes a notion of coordination expressed as the requirement of a Coordinated Discourse Topic (CDT). CDT characterizes a class of discourse relations, among which are Narration and Result. Once the basic semantic contribution of "and" is isolated, effects related to its presence such as changes in temporal structure, blocking of a Discourse Relation, or conditional meanings are shown to follow from the defeasible architecture set up by SDRT.