Situated Conditional Reasoning

TL;DR

This paper introduces situation-based conditionals that are more expressive than classical ones, capable of capturing nuanced information like expectations and counterfactuals, with a formal semantics and an efficient reasoning method.

Contribution

It formalizes situation-based conditionals, provides a semantics and representation theorem, and develops a computationally feasible entailment method called minimal closure.

Findings

Situation-based conditionals generalize classical conditionals.

A formal semantics and rationality postulates are established.

Minimal closure can be computed via propositional entailment checks.

Abstract

Conditionals are useful for modelling, but are not always sufficiently expressive for capturing information accurately. In this paper we make the case for a form of conditional that is situation-based. These conditionals are more expressive than classical conditionals, are general enough to be used in several application domains, and are able to distinguish, for example, between expectations and counterfactuals. Formally, they are shown to generalise the conditional setting in the style of Kraus, Lehmann, and Magidor. We show that situation-based conditionals can be described in terms of a set of rationality postulates. We then propose an intuitive semantics for these conditionals, and present a representation result which shows that our semantic construction corresponds exactly to the description in terms of postulates. With the semantics in place, we proceed to define a form of entailment for situated conditional knowledge bases, which we refer to as minimal closure. It is reminiscent of and, indeed, inspired by, the version of entailment for propositional conditional knowledge bases known as rational closure. Finally, we proceed to show that it is possible to reduce the computation of minimal closure to a series of propositional entailment and satisfiability checks. While this is also the case for rational closure, it is somewhat surprising that the result carries over to minimal closure.