The nets of reason

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 twentieth century saw a deep split. Perelman and 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 of 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 and Krabbe 1995; van Eemeren and Grootendorst 2004). But this split was not inevitable, and it was not forever. Already Lorenzen (1955) used innovative game-theoretical 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 Artificial Intelligence, which turned out to have strong connections to computational logics.