The Logic And Thinking Of AGM Theory And Conditional

Belief revision theory began in1970s,one of its most striking theories is theAlchourrón、G rdenfors and Makinson jointly established the theory of beliefrevision,referred to as the AGM theory.In this paper, through a series of discussionsand proofs to interpret a more comprehensive system of AGM′s theory.This article divides into four chapters.The first chapter is the overview of theAGM program.The AGM program of belief revision have two sources.G rdenforsprovided a semantics for Lewis’s logic of conditionals in terms of belief revisionmodels. Alchourrón and Makinson studied the dynamics of normative systems. I hopethis chapter will focus on the former strand of research which initiated belief revisionresearch. It contains eight kinds of postulates are Closure, Success, Inclusion, Vacuity,Consistency, Extensionality, Superexpansion and Subexpansion.The second chapter is AGM function.This chapter is concerned with formalaspects of the logic of theory change. The chapter defines a concept of "safecontraction" of a set of propositions, proves that it satisfies the G rdenfors postulatesfor contraction and therefore can be expressed as a partial meet contraction, andstudies its properties both in general and under various natural constraints.The third chapter is iterable AGM function.In this chapter, Our study is themost basic scheme of iteration: an iterative function.We construct an iterable versionof the AGM model, indicating that the AGM for malism is in fact compatible.Following Alchourrón and Makinson′s early reference to an iterable form of a safecontraction function,we provide an iterable structure for each of the five AGMpresentations(meet functions,systems of spheres,postulates,epistemic entrenchmentsand safe hierarchies)and prove their equivalence.The forth chapter is the reflection to the theory of the AGM. AGM theoryshortly after its formation, G rdenfors discovered that things were much moreproblematic. The AGM theory used in the conditional sentences have also beenpointed out that there are two problems. In this chapter the author analyzing theseproblems, and puts forward some reflection and suggestions.