Iterated Conditionals and Characterization of P-entailment

TL;DR

This paper explores the properties of iterated conditionals within the framework of coherence, providing new characterizations of p-entailment and demonstrating that certain iterated conditionals are constant and equal to 1.

Contribution

It introduces a novel approach to defining and analyzing iterated conditionals and their relation to p-entailment in the coherence framework.

Findings

The prevision of the conjunction of conditionals equals the product of the previsions of the iterated and initial conditionals.

The iterated conditional $(E_{n+1}|H_{n+1})|\mathscr{C}(\mathcal{F})$ is constant and equal to 1 when $\mathcal{F}$ p-entails $E_{n+1}|H_{n+1}$.

The characterization of p-entailment via constant iterated conditionals is validated through an example related to weak transitivity.

Abstract

In this paper we deepen, in the setting of coherence, some results obtained in recent papers on the notion of p-entailment of Adams and its relationship with conjoined and iterated conditionals. We recall that conjoined and iterated conditionals are suitably defined in the framework of conditional random quantities. Given a family $\mathcal{F}$ of $n$ conditional events $\{E_1|H_1,\ldots, E_n|H_n\}$ we denote by $\mathscr{C}(\mathcal{F})=(E_1|H_1)\wedge \cdots \wedge (E_n|H_n)$ the conjunction of the conditional events in $\mathcal{F}$. We introduce the iterated conditional $\mathscr{C}(\mathcal{F}_2)|\mathscr{C}(\mathcal{F}_1)$, where $\mathcal{F}_1$ and $\mathcal{F}_2$ are two finite families of conditional events, by showing that the prevision of $\mathscr{C}(\mathcal{F}_2)\wedge \mathscr{C}(\mathcal{F}_1)$ is the product of the prevision of $\mathscr{C}(\mathcal{F}_2)|\mathscr{C}(\mathcal{F}_1)$ and the prevision of $\mathscr{C}(\mathcal{F}_1)$. Likewise the well known equality $(A\wedge H)|H=A|H$, we show that $ (\mathscr{C}(\mathcal{F}_2)\wedge \mathscr{C}(\mathcal{F}_1))|\mathscr{C}(\mathcal{F}_1)= \mathscr{C}(\mathcal{F}_2)|\mathscr{C}(\mathcal{F}_1)$. Then, we consider the case $\mathcal{F}_1=\mathcal{F}_2=\mathcal{F}$ and we verify for the prevision $\mu$ of $\mathscr{C}(\mathcal{F})|\mathscr{C}(\mathcal{F})$ that the unique coherent assessment is $\mu=1$ and, as a consequence, $\mathscr{C}(\mathcal{F})|\mathscr{C}(\mathcal{F})$ coincides with the constant 1. Finally, by assuming $\mathcal{F}$ p-consistent, we deepen some previous characterizations of p-entailment by showing that $\mathcal{F}$ p-entails a conditional event $E_{n+1}|H_{n+1}$ if and only if the iterated conditional $(E_{n+1}|H_{n+1})\,|\,\mathscr{C}(\mathcal{F})$ is constant and equal to 1. We illustrate this characterization by an example related with weak transitivity.