Jeffrey Conditionalization and Value Changes. Episteme (2025). https://doi.org/10.1017/epi.2025.10047
Abstract: Gallow (2019) has proposed an ingenious accuracy-first vindication that our credence should be updated in accordance with conditionalization. This paper extends his idea to cases where we undergo only a partial learning experience. In particular, I attempt to vindicate, in the spirit of accuracy-first epistemology, that when we undergo what is called `Jeffrey partial learning' in this paper, our credences should be updated in accordance with Jeffrey conditionalization, or at the very least, the update should be rigid. In doing so, I propose what I call the `Jeffrey-accuracy function.' This function is not strictly proper and, at first glance, seems to rationalize ill-motivated credence updating. However, this turns out not to be the case.
Evidence and the Epistemic Betterness. Synthese 202, 119 (2023). https://doi.org/10.1007/s11229-023-04350-9
Abstract: It seems intuitive that our credal states are improved if we obtain evidence favoring truth over any falsehood. In this regard, Fallis and Lewis have recently provided and discussed some formal versions of such an intuition, which they name `the Monotonicity Principle' and `Elimination'. They argue, with those principles in hand, that the Brier rule, one of the most popular rules of accuracy, is not a good measure, and that accuracy-firsters cannot underwrite both probabilism and conditionalization. In this paper, I will argue that their conclusions are somewhat hasty. Specifically, I will demonstrate that there is another version of the Monotonicity Principle that can be satisfied by some additive rules of accuracy, such as the Brier rule. Moreover, it will also be argued that their version of the principle has some undesirable features regarding the epistemic betterness. Therefore, their criticisms can hardly jeopardize accuracy-firsters until any further justification of their versions of the Monotonicity Principle and Elimination is provided.
Infinite Opinion Sets and Relative Accuracy. Journal of Philosophy 120 (6): 285-313. 2023. (with Jaemin Jung)
Abstract: We can have credences in an infinite number of propositions---that is, our opinion set can be infinite. Accuracy-first epistemologists have devoted themselves to evaluating credal states with the help of the concept of ‘accuracy’. Unfortunately, the infinite opinion sets, under several innocuous assumptions, yield several undesirable results, some of which are even fatal, to accuracy-first epistemology. Moreover, accuracy-first epistemologists cannot circumvent these difficulties in any standard way. In this regard, we will suggest a non-standard approach, called a relativistic approach, to accuracy-first epistemology and show that such an approach can successfully circumvent undesirable results while having some advantages over the standard approach.
Dutch Book Arguments for Epistemic Optimism. CHUL HAK SA SANG - Journal of Philosophical Ideas 86 (86): 229-263. 2022.
Abstract: This paper intends to formulate and justify two versions of epistemic optimism: Credence-based Optimism and Accuracy- based Optimism. It is first shown, using a bet with non-fixed stake, that there is a Dutch book that seems to lead every belief updater to a sure loss (Section 2.1). With the help of this result and some decision-theoretic considerations, I derive one version of epistemic optimism, which is called ‘Credence-based Optimism’, and then show that any belief updater who violates the kind of optimism is vulnerable to a sure loss (Sections 2.2-2.3). After formulating and justifying Credence-based Optimism, I point out a problem that besets such a kind of optimism (Section 3.1) and then formulate another kind of optimism, which is called ‘Accuracy-based Optimism’, using the concept of accuracy (Section 3.2). In addition, I provide a diachronic Dutch Book Argument for Accuracy-Based Optimism (Section 3.3). Lastly, these two kinds of optimism are compared with Reflection. In doing so, we can ascertain the theoretical status of the epistemic optimism in question (Section 4).
Correcting Credences with Chances. Synthese 198 (1): 509-536. 2021.
Abstract: Lewis’s Principal Principle is widely recognized as a rationality constraint that our credences should satisfy throughout our epistemic life. In practice, however, our credences often fail to satisfy this principle because of our various epistemic limitations. Facing such violations, we should correct our credences in accordance with this principle. In this paper, I will formulate a way of correcting our credences, which will be called the Adams Correcting Rules and then show that such a rule yields non-commutativity between conditionalizing and correcting. With the help of the notion of ‘accuracy’, then, I attempt to provide a vindica- tion of the Adams Correcting Rule and show how we can respond to the non- commutativity in question.
The Principal Principle and Posterior Credence. Korean Journal for the Philosophy of Science 19(2): 1-17. 2016.
Abstract: In this paper, I will show that, contrary to what many philosophers of chance have thought, Lewis’s original Principal Principle itself does not stay silent on how our posterior credences should be related to chances. Furthermore, I will prove, with the help of this result, that Nissan-Rozen (2013) fails to show that the Principal Principle is not preserved under Jeffrey Conditionalization. Indeed, the Principal Principle is preserved under any coherent belief updating rule.
Confirmation Measures and Collaborative Belief Updating. Synthese 191 (16): 3955-3975. 2014.
Abstract: There are some candidates that have been thought to measure the degree to which evidence incrementally confirms a hypothesis. This paper provides an argument for one candidate—the log-likelihood ratio measure. For this purpose, I will suggest a plausible requirement that I call the Requirement of Collaboration. And then, it will be shown that, of various candidates, only the log-likelihood ratio measure l satisfies this requirement. Using this result, Jeffrey conditionalization will be reformulated so as to disclose explicitly what determines new credences after experience.
Simultaneous Belief Updates Via Successive Jeffrey Conditionalization. Synthese 190 (16):3511-3533. 2013.
Abstract: This paper discusses simultaneous belief updates. I argue here that modeling such belief updates using the Principle of Minimum Information can be regarded as applying Jeffrey conditionalization successively, and so that, contrary to what many probabilists have thought, the simultaneous belief updates can be successfully modeled by means of Jeffrey conditionalization.
Rescuing Reflection. Philosophy of Science 79 (4):473-489. 2012.
Abstract: In this article, I suggest an argument that seems to show a conflict between the reflection principle and conditionalization. In particular, I show that when the reflection principle is formulated in a standard way, the principle conflicts with Jeffrey conditionalization. And it is argued that the source of the conflict resides in an ambiguity of the standard formulation. Furthermore, I attempt to rescue the principle using Bayes factors. That is, I suggest a new formulation of the principle so as to avoid the conflict.