The nets of reason

Abstract

History in fast-forward Logic and argumentation are a natural combination. Though the precise origins of logic are hidden in the mists of antiquity, reflection on patterns in legal or philosophical debate may have been one of the driving forces in the genesis of the discipline. But afterwards, the main emphasis over time shifted to consequence relations in an abstract universe of propositions, and the formal systems to which these give rise. Though contacts were never lost entirely between logic and the realities of discussion and debate, the 20 century saw a deep split. Perelman & Olbrechts-Tyteca 1958 pointed out how actual reasoning may be more like weaving a piece of cloth from many threads than forging a chain with links in linear mathematical proof style, and rhetoric and informal logic then took their own course. Likewise, Toulmin 1958 made a powerful case how legal procedure and functional schemas – ‘formalities’ rather than logical form – may be the best paradigm for understanding argumentation. Both critics have inspired follow-up frameworks that continue to flourish today (cf. Walton & Krabbe 1995, van Eemeren & Grootendorst 2004). But this split was not inevitable, and it was not forever. Already Lorenzen 1955 used innovative gametheoretical models of dialogue to investigate the foundations of logic, and in more recent times, Dung 1995 introduced formal models of argumentation in a setting of AI, which turned out to have strong connections to computational logics.