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Applying labelled deductive systems and multi-agent systems to source-based argumentation
Department of Philosophy, University of Winnipeg, Winnipeg, Manitoba, R3B 2E9 Canada. E-mail: walton@io.uwinnipeg.ca
In this paper, it is shown how labelled deductive systems and multi-agent systems can be used to evaluate argumentation that is source-based and depends on a credibility function. When agents engage in argumentation in dialogues, each agent has a credibility function that can be adjusted upwards or downwards by certain types of arguments brought forward by the other agent in the dialogue. One type is the argument against the person or argumentum ad hominem, in which personal attack on one party's character is used to attack his argument. Another is the appeal to expert opinion, traditionally associated with the informal fallacy called the argumentum ad verecundiam. Both types of argument are frequently used in legal argumentation, sometimes fallaciously and sometimes non-fallaciously. The problem is to have some kind of structure that can be used to identify the form of the argument, and to appraise how the form has been used in specific cases, in order to determine which cases represent fallacious uses of argumentation, and which do not. Part of the system is dialectical, meaning that it views the argumentation in light of its use in a collaborative communicative exchange, or so-called dialogue, between two agents.
Key words: Legal argumentation, credibility, dialogues, witness testimony, fallacies, evidence, ad hominem arguments, practical reasoning, ad verecundiam arguments, agent communication, expert system.