# Reasoning by Cases in Structured Argumentation

## TL;DR

This paper extends the ASPIC+ framework for structured argumentation to incorporate reasoning by cases, enabling defeasible arguments with disjunctive conclusions and highlighting the complexities of defeasible reasoning with disjunctive information.

## Contribution

It introduces a novel extension to ASPIC+ for reasoning by cases, providing a formal approach to handle disjunctive information in defeasible argumentation.

## Key findings

- Different results from other non-monotonic logic approaches
- Formalization of reasoning with disjunctive information is complex
- Raises new questions about defeasible reasoning subtleties

## Abstract

We extend the $ASPIC^+$ framework for structured argumentation so as to allow applications of the reasoning by cases inference scheme for defeasible arguments. Given an argument with conclusion `$A$ or $B$', an argument based on $A$ with conclusion $C$, and an argument based on $B$ with conclusion $C$, we allow the construction of an argument with conclusion $C$. We show how our framework leads to different results than other approaches in non-monotonic logic for dealing with disjunctive information, such as disjunctive default theory or approaches based on the OR-rule (which allows to derive a defeasible rule `If ($A$ or $B$) then $C$', given two defeasible rules `If $A$ then $C$' and `If $B$ then $C$'). We raise new questions regarding the subtleties of reasoning defeasibly with disjunctive information, and show that its formalization is more intricate than one would presume.