Abstract

Metaphor has long been regarded as a peripheral, sometimes deviant part of language, and even with the increasing attention it has received of late, most programming attempts to capture natural language still ignore this pervasive and difficult aspect of speech. Psychological studies of metaphor and other 'nonliteral' utterances have shown that when the context is sufficiently defined, comprehension of figurative speech is just as rapid as comprehension for literal speech. This suggests that metaphor is just as central to language as literal speech. In fact, considering the extent to which it permeates language, metaphor can be seen as a valuable clue as to the kind of cognitive processes that underlie speech. ;The Dynamic Type Hierarchy theory presents an analysis of metaphor that incorporates John Sowa's theory of Conceptual Graphs with Max Black's interaction view of metaphor. A new approach to type hierarchies is developed, one which gives a new interpretation to the relation among concept nodes and the mechanisms of inheritance, and one that recommends a particular mathematical structure. Furthermore, these hierarchies are seen as dynamic rather than static, and mechanisms for their adaptation and rearrangement are introduced. Type hierarchies and the associated schemata that represent background knowledge in a system are seen as modelling the ontology of the speaker/hearer's internal world. Metaphor is seen as a method of generating new perspectives and new concepts in terms of the internal models possessed prior to its comprehension. ;Impossibility arguments against natural language processing are considered, and they are seen to rest, in a large part, on the doctrines of ordinary language philosophy and criticisms of ideal language. It is argued that natural language processing need not be committed to the rigid view of language that has been attributed to it. Furthermore, language extension and shifts in the application of terms that are part of ordinary language are seen as related to the mechanisms of metaphor comprehension and generation. The dynamic type hierarchy theory is then used to explicate natural language phenomena such as open texture, context, family resemblances and concept formation