Juhani Yli-Vakkuri

We explore the consequences of a natural and well-motivated modeling assumption of Bayesian epistemology, according to which the objects of credence are sentences in the agent's language. We show that this assumption is inconsistent with two further natural Bayesian idealizations: those of Logical Perfection (the logical-deductive consistency and closure of the sentences in which the agent is certain) and of perfect access to (i.e., certainty regarding) the presence or absence of certainty in any particular sentence in the agent's language—an assumption we call “Luminosity.” That is, it turns out that a luminous agent is an irrational agent. After presenting our main result and some related impossibility results concerning variations on Logical Perfection and Luminosity, we briefly examine the range of candidate solutions to the puzzles that these results present us with.

In 1968, David Lewis provided a translation scheme from the language of quantified modal logic (QML) into the language of counterpart theory (CT), one that he thought would make manifest the truth conditions of absolute or metaphysical modal claims. Lewis’s other main contribution to the logic and semantics of modality is his celebrated 1973 semantics for counterfactual conditionals, which is put forward as a more general theory that subsumes the logic of metaphysical modality. It is natural for the advocate of CT to wish to extend Lewis’s 1968 translation scheme for QML to a language that includes the counterfactual conditional connective. This chapter first examines the translation of QML to counterpart theory proposed by Lewis in 1973, making vivid various challenges that confront anyone wishing to marry counterpart theory with a logic of counterfactuals. It then proposes a superior translation scheme within the framework of Lewis’s own counterpart theory.

This chapter explores solutions to a somewhat underappreciated family of puzzles concerning propositional attitudes generated by intensionalism—the view that necessarily equivalent propositions are identical. After presenting the puzzles informally, the chapter introduces the apparatus of higher-order logic, which allows one to quantify into the position of any type of expression, and makes possible a formally rigorous statement of the puzzles. Many philosophers will think that it’s quite obvious how one should respond to the puzzles—namely by treating them as refutations of intensionalism. But this response is arguably too quick. The chapter explores strategies for responding to the puzzles within the framework of intensionalism, laying out a taxonomy of such strategies. Certain of these strategies treat English attitude sentences as opaque and others don’t. However all of them use a transparent (i.e. non-opaque) language as the vehicle for theorizing. The focus here will be on the logical ramifications of the various strategies.

The chapter argues that Menzies and List's defence of the claim that higher‐level properties have causal powers independent of those of their physical realizers conflates questions about the causal powers of properties with questions about their explanatory roles. Menzies and List's argument shows only that explanations in terms of higher‐level properties are sometimes more appropriate than explanations in terms of physical properties, but no conclusions about the causal powers of properties can be drawn from this without assuming a questionable version of the interventionist theory of causation.

In ‘The Nature of Content: A Critique of Yli-Vakkuri and Hawthorne’, Sarah Sawyer argues that we failed to attend to the fundamental distinction between indexical and non-indexical thought in Narrow Content, and for that reason the efficacy of our arguments against the narrow content theorist is seriously impaired. Sawyer is right that that distinction does not figure prominently in our book. However, for reasons we made manifest, that distinction does not offer a promising basis for developing a theory of narrow content. In what follows we will speak to this theme, as well as addressing some important matters of detail.

We explore the consequences of a natural and well‐motivated modeling assumption of Bayesian epistemology, according to which the objects of credence are sentences in the agent's language. We show that this assumption is inconsistent with two further natural Bayesian idealizations: those of Logical Perfection (the logical‐deductive consistency and closure of the sentences in which the agent is certain) and of perfect access to (i.e., certainty regarding) the presence or absence of certainty in any particular sentence in the agent's language—an assumption we call “Luminosity.” That is, it turns out that a luminous agent is an irrational agent. After presenting our main result and some related impossibility results concerning variations on Logical Perfection and Luminosity, we briefly examine the range of candidate solutions to the puzzles that these results present us with.

In an anonymous referee report written in 1945, Church suggested a sweeping argument against verificiationism, the thesis that every truth is knowable. The argument, which was published with due acknowledgement by Fitch almost two decades later, has generated significant attention as well as some interesting successor arguments. In this paper, we present the most important episodes in this intellectual history using the logic that Church himself favoured, and we give reasons for thinking that the arguments are less than decisive. However, we present some new arguments against verificationism that we believe to be dialectically effective.

This paper presents a new system of logic, LF, that is intended to be used as the foundation of the formalization of science. That is, deductive validity according to LF is to be used as the criterion for assessing what follows from the verdicts, hypotheses, or conjectures of any science. In work currently in progress, we argue for the unique suitability of LF for the formalization of logic, mathematics, syntax, and semantics. The present document specifies the language and rules of LF, lays out some notational conventions, and states some basic technical facts about the system.

In general, a given object could have been different in certain respects. For example, the Great Pyramid could have been somewhat shorter or taller; the Mona Lisa could have had a somewhat different pattern of colours; an ordinary table could have been made of a somewhat different quantity of wood. But there seem to be limits. It would be odd to suppose that the Great Pyramid could have been thimble-sized; that the Mona Lisa could have had the pattern of colours that actually characterizes The Scream; or that the table could have been made of the very quantity of wood that in fact made some other table. However, there are puzzling arguments that purport to show that so long as an object is capable of being somewhat different in some respect, it is capable of being radically different in that respect. These arguments rely on two tempting thoughts: first, that an object’s capacity for moderate variation is a non-contingent matter, and second, that what is possibly possible is simply possible. This book systematically investigates competing strategies for resolving these puzzles, and defends one of them. Along the way it engages with foundational questions about the metaphysics of modality.

The concept of being in a position to know is an increasingly popular member of the epistemologist’s toolkit. Some have used it as a basis for an account of propositional justification. Others, following Timothy Williamson, have used it as a vehicle for articulating interesting luminosity and anti-luminosity theses. It is tempting to think that while knowledge itself does not obey any closure principles, being in a position to know does. For example, if one knows both p and ‘If p then q’, but one dies or gets distracted before being able to perform a modus ponens on these items of knowledge and for that reason one does not know q, one is still plausibly in a position to know q. It is also tempting to suppose that, while one does not know all logical truths, one is nevertheless in a position to know every logical truth. Putting these temptations together, we get the view that being in a position to know has a normal modal logic. A recent literature has begun to investigate whether it is a good idea to give in to these twin temptations—in particular the first one. That literature assumes very naturally that one is in a position to know everything one knows and that one is not in a position to know things that one cannot know. It has succeeded in showing that, given the modest closure condition that knowledge is closed under conjunction elimination, being a position to know cannot satisfy the so-called K axiom of normal modal logics. In this paper, we explore the question of the normality of the logic of being in a position to know in a more far-reaching and systematic way. Assuming that being in a position to know entails the possibility of knowing and that knowing entails being in a position to know, we can demonstrate radical failures of normality without assuming any closure principles at all for knowledge. Moreover, the failure of normality cannot be laid at the door of the K axiom for knowledge, since the standard principle NEC of necessitation also fails for being in a position to know. After laying out and explaining our results, we briefly survey the coherent options that remain.

In this reply to Paul Pietroski’s comment on our book Narrow Content, we address his concern that we assume too tight a connection between sentences and contents and thus ignore polysemy. We argue that we were not relying on problematic disquotational assumptions and that our arguments are fully compatible with rampant polysemy. We also argue that Pietroski’s strategy of making room for a theoretically interesting kind of narrow content by giving up the idea that contents determine extensions at indices doesn’t save him from our “Mirror Man” counterexamples. We argue finally that narrow polyadic relations of the sort that feature in our final chapter are better suited than narrow content assignments for Pietroski’s explanatory needs.

In this reply to Alex Byrne’s comment on our book Narrow Content, we address Byrne’s claim that internalism is best framed as a thesis about properties of agents rather than properties of thoughts, arguing that a thought-based framework is better suited to standard internalist ambitions. We also discuss whether there is any prospect for a view in the internalist spirit that prescinds from multiplying indices beyond worlds, address Byrne’s ordinary language considerations against an ontology of thoughts, and briefly evaluate the prospects for giving narrow content ascriptions explanatory life by using them to give an account of how things perceptually seem.

How does vagueness interact with metaphysical modality and with restrictions of it, such as nomological modality? In particular, how do definiteness, necessity (understood as restricted in some way or not), and actuality interact? This paper proposes a model-theoretic framework for investigating the logic and semantics of that interaction. The framework is put forward in an ecumenical spirit: it is intended to be applicable to all theories of vagueness that express vagueness using a definiteness (or: determinacy) operator. We will show how epistemicists, supervaluationists, and theorists of metaphysical vagueness like Barnes and Williams (2010) can interpret the framework.  We will also present a complete axiomatization of the logic we recommend to both epistemicists and local supervaluationists. 

The epistemology of modality has focused on metaphysical modality and, more recently, counterfactual conditionals. Knowledge of kinds of modality that are not metaphysical has so far gone largely unexplored. Yet other theoretically interesting kinds of modality, such as nomic, practical, and ‘easy’ possibility, are no less puzzling epistemologically. Could Clinton easily have won the 2016 presidential election—was it an easy possibility? Given that she didn’t in fact win the election, how, if at all, can we know whether she easily could have? This paper investigates the epistemology of the broad category of ‘objective’ modality, of which metaphysical modality is a special, limiting case. It argues that the same cognitive mechanisms that are capable of producing knowledge of metaphysical modality are also capable of producing knowledge of all other objective modalities. This conclusion can be used to explain the roles of counterfactual reasoning and the imagination in the epistemology of objective modality.

The idea that the epistemology of modality is in some sense a priori is a popular one, but it has turned out to be difficult to precisify in a way that does not expose it to decisive counterexamples. The most common precisifications follow Kripke’s suggestion that cases of necessary a posteriori truth that can be known a priori to be necessary if true ‘may give a clue to a general characterization of a posteriori knowledge of necessary truths’. The idea is that whether it is contingent whether p can be known a priori for at least some broad range of sentences ‘p’. Recently, Al Casullo and Jens Kipper have discussed restrictions of such principles to atomic sentences. We show that decisive counterexamples even to such dramatically restricted Kripke-style principles can be constructed using minimal logical resources. We then consider further restrictions, and show that the counterexamples to the original principles can be turned into counterexamples to the further restricted principles. We conclude that, if there are any true restrictions of Kripke-style principles, then they are so weak as to be of little epistemological interest.

Michael Fara's ‘habitual analysis’ of disposition ascriptions is equivalent to a kind of ceteris paribus conditional analysis which has no evident advantage over Martin's well known and simpler analysis. I describe an unsatisfactory hypothetical response to Martin's challenge, which is lacking in just the same respect as the analysis considered by Martin; Fara's habitual analysis is equivalent to this hypothetical analysis. The feature of the habitual analysis that is responsible for this cannot be harmlessly excised, for the resulting analysis would be subject to familiar counter-examples

What kind of semantics should someone who accepts the epistemicist theory of vagueness defended in Timothy Williamson’s Vagueness (1994) give a definiteness operator? To impose some interesting constraints on acceptable answers to this question, I will assume that the object language also contains a metaphysical necessity operator and a metaphysical actuality operator. I will suggest that the answer is to be found by working within a three-dimensional model theory. I will provide sketches of two ways of extracting an epistemicist semantics from that model theory, one of which I will find to be more plausible than the other.