PRINCIPIA 26(1): 135–152 (2022) doi: 10.5007/1808-1711.2022.e84677 Published by NEL — Epistemology and Logic Research Group, Federal University of Santa Catarina (UFSC), Brazil. WHAT IS THE AIM OF MODELS IN FORMAL EPISTEMOLOGY? MATHEUS DE LIMA RUI Federal University of Santa Catarina, BRAZIL matheus.lrui@gmail.com Abstract. It is certainly well accepted that formal models play a key role in scientific job. Its use goes from natural sciences like physics and even to social sciences like economics and politics. Using mathematics allows the researcher to consider more complicated scenarios in- volving several variables. Some models are developed to make predictions, others to describe a phenomena, or just to improve the explanation of events in the world. But what has all this to do with philosophy? The aim of the present paper is to investigate debates on the role of formal models in a specific philosophical subject, precisely, the epistemology of rationality. Are we able to explain why models are needed in epistemological work? This answer will be addressed on the assumptions that epistemological theorizing is committed with normative statements. More specifically, epistemologists are concerned with normative questions about what rationality requires from epistemic agents. The first goal is to discuss some assumptions about the role of mathematical models in formal epistemology undertaking. And secondly, I will argue for the following two claims: (i) formal models are useful tools for predicting consequences of normative assumption about what is intuitively required by rationality; and (ii) insofar rationality theory is normative in virtue of being instrumentalist and aiming at truth, formal models are means-end tools, therefore, for rationality, mathematical models are devices for maximizing truth in doxastic states. Keywords: Belief • idealization • formal-epistemology • models • rationality RECEIVED: 01/11/2021 REVISED: 11/03/2022 ACCEPTED: 02/04/2022 1. Introduction It is certainly well accepted that formal models play a key role in scientific job. This has been true for centuries in natural sciences like physics and chemistry, and more recently for social sciences like economics and politics. In philosophy, only in the last few decades the discussion around the use of formal models as a genuine philosophi- cal tool has received proper attention (although formal tools in philosophical activity has been used for more than a century). In the present paper I am concerned with the use of formal models in a specific philosophical domain, that is, the epistemology of rationality. In this piece I discuss why, despite the controversies, the use of formal models in the epistemological undertaking can better off our small box of methodological tools © 2022 The author(s). Open access under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License.