Defaults and Normality in Causal Structures

TL;DR

This paper improves the Halpern-Pearl causality definition by integrating defaults, clarifies the nature of causes, and compares it with Wright's NESS test, providing conditions for their equivalence.

Contribution

It introduces a combined causality and default theory, clarifies that causes need not be single conjuncts, and establishes conditions for equivalence with the NESS test.

Findings

A defect in the HP causality definition is repaired.

Causes according to HP need not be single conjuncts.

Conditions are provided for equivalence with the NESS test.

Abstract

A serious defect with the Halpern-Pearl (HP) definition of causality is repaired by combining a theory of causality with a theory of defaults. In addition, it is shown that (despite a claim to the contrary) a cause according to the HP condition need not be a single conjunct. A definition of causality motivated by Wright's NESS test is shown to always hold for a single conjunct. Moreover, conditions that hold for all the examples considered by HP are given that guarantee that causality according to (this version) of the NESS test is equivalent to the HP definition.