A Plausible, Incremental Strong AI Account
	       of the Origin and Evolution of Language

			    Jerry R. Hobbs
		    Artificial Intelligence Center
			  SRI International

I assume an abductive account of interpretation in general, in which to
interpret a situation is to find the best explanation for the
observables.  I also assume an abductive account of discourse
interpretation, in which to interpret a sentence is to find the best
proof of its logical form, allowing assumptions, with respect to a
knowledge base consisting of Horn clause axioms.  Increases in knowledge
of language, whether in learning, development, or evolution, are seen as
results of incremental modifications on the axioms, axiomatizations of
common proofs, and the employment of theories motivated independently of
language.  Within this framework, I describe how two of the principal
features of language could have evolved -- Gricean nonnatural meaning
and syntactic structure.  The development of Gricean meaning is seen as
the employment of increasingly complex folk theories in the
interpretation of utterances as actions.  The development of syntactic
structure is seen as increasingly specific constraints on the
interpretation of the adjacency and proximity of strings of words as
expressing predicate-argument relations.  One of the principal
difficulties
in understanding the origin and evolution of language is in imagining 
plausible, incremental, intermediate steps.  This talk seeks to begin
to remedy this situation.