A Logical Investigation into Suspension

• Applicant: Wei Zhu, Ph.D.
• Subject Area: Theoretical Philosophy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555902497

The term “suspension” often indicates a propositional attitude, i.e., one neither believes nor disbelieves a proposition. This project will study suspension by combining many-valued logics with models from belief revision theories, to provide a formal system of rational suspension and belief. I have three research objectives. The first objective aims to extend the current literature on suspension into the area of many-valued logics by addressing two main questions. The first question asks whether the suspension we talk about keeps the same, if the propositional logic is many-valued. That is, since suspension is assumed to be a propositional attitude, if the propositional logic is many-valued, does it change the nature of suspension, and what is the relationship between suspension and many-valued logics? The second question asks in what ways many-valued logics can contribute new insights to suspension. That is, since the central idea of all many-valued logics is that instead of being either true or false, some propositions can have indeterminate truth value. If we apply a many-valued logic to suspension, we can therefore expect new implications from a logical aspect. The second objective aims to characterize suspension and its relationship with belief in an AGM-style belief revision model based on a three-valued logic. I will answer two main questions. The first question is about how to define the main components of an AGM-style model based on a three-valued logic. The second question is how to characterize suspension as a basic epistemic change operation. The research outcomes and views developed in the first objective will be used to solve problems in this objective. The third objective aims to relate suspension with deliberative whether-questions. I have two main questions. The first one is how to define and analyse a deliberative whether-question in an AGM-style model. Since epistemic inputs in AGM-style models are assumed to be sentences or propositions, then it is natural to ask how to include questions in one’s belief-changing process. The second one is about how to characterize suspension by relating one’s belief revision process to a correspondent deliberation process on a whether-question.

• DFG Programme: WBP Position