Question-relative knowledge for minimally rational agents

Abstract

Agents know some but not all logical consequences of what they know. Agents seem to be neither logically omniscient nor logically incompetent. Yet finding an intermediate standard of minimal rationality has proven difficult. In this paper, I take suggestions found in the literature [Lewis, D. 1988. Relevant Implication. Theoria 54 (3): 161174. https://doi.org/10.1111/theo.1988.54.issue-3; Hawke, P., A. Özgün, and F. Berto. 2020. The Fundamental Problem of Logical Omniscience. Journal of Philosophical Logic 49 (4): 727766. https://doi.org/10.1007/s10992-019-09536-6; Plebani, M., and G. Spolaore. 2021. Subject Matter: A Modest Proposal. The Philosophical Quarterly 71 (3): 605622. https://doi.org/10.1093/pq/pqaa054] and join the forces of subject matter and impossible worlds approaches to devise a new solution to this quandary. I do so by combining a space of FDE worlds [Berto, F., and M. Jago. 2019. Impossible Worlds. Oxford University Press.] with a Lewisian (1988) understanding of subject matters as partitions. By doing so, I show how subject matters impose some order in the anarchic space of FDE worlds, while the worlds allow for distinctions between contents which would not otherwise be available. Combining the two approaches, then, brings us closer to the desired closure principles for knowledge of minimally rational agents.