Gustavo Lacerda

We outline an abstract approach to defeasible reasoning and argumentation which
includes many existing formalisms, including default logic, extended logic programming,
non-monotonic modal logic and auto-epistemic logic, as special cases. We show, in particular,
that the admissibility" semantics for all these formalisms has a natural argumentation theoretic
interpretation and proof procedure, which seem to correspond well with informal
argumentation.

We present a family of dialectic proof procedures for the admissibility semantics
of assumption-based argumentation. These proof procedures are defined for any
conventional logic formulated as a collection of inference rules and show how any
such logic can be extended to a dialectic argumentation system.
The proof procedures find a set of assumptions, to defend a given belief, by starting
from an initial set of assumptions that supports an argument for the belief
and adding defending assumptions incrementally to counter-attack all attacks.
...
The novelty of our
approach lies mainly in its use of backward reasoning to construct arguments
and potential arguments, and the fact that the proponent and opponent can
attack one another before an argument is completed. The definition of winning
strategy can be implemented directly as a non-deterministic program, whose
search strategy implements the search for defences.

In conventional logic, beliefs are derived from axioms, which are held to be beyond
dispute. In everyday argumentation, however, beliefs are based on assumptions, which
can be questioned and disputed...

The purpose of this paper is to study the fundamental mechanism, humans use in
argumentation, and to explore ways to implement this mechanism on computers.
Roughly, the idea of argumentational reasoning is that a statement is believable if it can be
argued successfully against attacking arguments.

The book starts with a beautiful argument from Galileo's Two New Sciences (refuting Aristotelian belief on the influence of gravity on bodies of different weight). This is what makes this book far beyond the ordinary: it contains a wealth of instructive examples about the natural world, about society, about policy, about philosophy, and so on. These are not the usual made-up examples, but REAL ARGUMENTS: ranging from numerous samples of scientific argumentation to some more mundane arguments from newspapers. The author further introduces an informal method for analyzing (extracting and evaluating) arguments as they occur in ordinary language texts. The book not only offers an accessible introduction to critical analysis of theoretical argumentation occurring in informal texts. It is also of interest for logicians who want to have a better understanding of the considerations involved in analyzing unformalized arguments. This amounts, in my opinion, to a successful marriage between the insights from logic and the demands from reasoning patterns as they occur in substantive texts.