{"type":"ScholarlyArticle","title":"Merging Beliefs and Counterfactuals","authors":[{"name":"Emiliano Lorini","slug":"emiliano-lorini","given":"Emiliano","family":"Lorini","affiliation":""},{"name":"Dmitry Rozplokhas","slug":"dmitry-rozplokhas","given":"Dmitry","family":"Rozplokhas","affiliation":""}],"abstract":"We present a unified framework for modeling\r\nagents’ epistemic states and counterfactual conditionals. \r\nThe novelty of our approach lies at the\r\nsemantic level. We introduce a computationally\r\ngrounded semantics in which an agent’s doxastic\r\naccessibility relation, needed to model the standard \r\nnotion of deductively closed belief, is derived from the agent’s belief base, \r\nand in which the notion of comparative similarity between states,\r\nneeded to interpret counterfactual conditionals, is\r\ncomputed from both the atomic formulas describing \r\nthe agents’ belief bases and those describing\r\nthe environment. We use this semantics to interpret a language \r\nof beliefs and counterfactuals. We\r\ndemonstrate the expressiveness of our language and\r\nthe flexibility of the semantics by formalizing a\r\nwide range of notions: counterfactual dependence,\r\ncounterfactual notions of reason and knowledge,\r\nconditional belief. Furthermore, we show that our\r\nsemantics illuminates the subtle interplay between\r\nbelief change and counterfactuals. On the computational side, \r\nwe provide a succinct formulation of\r\nmodel checking for our language and establish a\r\nPSPACE complexity result.","doi":"10.24963/ijcai.2026/440","url":"https://ijcai.org/proceedings/2026/440","pdf":"https://ijcai.org/proceedings/2026/0440.pdf","markdown":"https://ijcai.org/proceedings/2026/440.md","bibtex":"https://ijcai.org/proceedings/2026/bibtex/440","volume":{"slug":"2026","title":"Proceedings of the Thirty-Fifth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2026","url":"https://ijcai.org/proceedings/2026/","year":2026,"location":"Bremen, Germany","dates":"15-21 August 2026","editors":"Diego Calvanese","isbn":"978-1-956792-09-6","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2026"},"section":"Knowledge Representation and Reasoning","track":"Main Track","number":440,"pages":{"first":3952,"last":3960},"keywords":["Knowledge Representation and Reasoning: Belief change","Knowledge Representation and Reasoning: Knowledge representation languages","Knowledge Representation and Reasoning: Reasoning about knowledge and belief"],"videos":[],"references":[],"license_note":"Copyright International Joint Conferences on Artificial Intelligence."}