I am a philosopher at the University of Edinburgh. I work in traditional areas of theoretical philosophy, often using methods from decision theory, formal semantics, and logic.
My CV (PDF).
Email: wo@umsu.de.
Research
Some of my research revolves around the idea that we are approximately Bayesian agents whose internal representation of the world involves extra parameters that do not track an independent dimension of objective reality. These parameters arguably include a marker for ourselves and the present time, the phenomenal character of sensory experiences, the options among which we choose, moral norms, and hypotheses about natural modality.
I also work on: rational speech act models of pragmatics, the semantics of conditionals and ability modals, attitude reports and the nature of propositional attitudes, dynamic norms for self-locating beliefs, Humeanism in metaphysics, the interpretation of probability in scientific theories, causal decision theory, model theory of quantified modal logic, and too many other topics.
Publications
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I try to make sense of our conception of agency, which seems to involve special acts of "willing" or "trying" that impinge on the physical world from the outside and are infallibly revealed to the agent.Forthcoming in B. Vetter and T. Schoonen (ed.), The Epistemology of Ability, Oxford: Oxford University Press 2026
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I discuss a range of phenomena surrounding the "Simplification of Disjunctive Antecedents" and argue for a pragmatic explanation.Forthcoming in B. Fitelson and J.J. Joaquin (ed.), Could, would, should: Essays in Honor of Alan Hájek, Springer 2026
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I explore how norms of diachronic rationality might apply to cases where it's unsure whether compliance with the ideal norms is possible, using the Sleeping Beauty problem as an example.
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I argue that rational agents shouldn't always proportion their beliefs to their evidence.
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I argue that anti-Humean accounts in metaphysics have trouble explaining how we can have knowledge of natural modality.
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I like possible-worlds models of knowledge and belief. These models don't allow for a priori enquiry. But then what is going on when we do metaphysics (or maths)?Helen Beebee and J.R.A. Fisher (ed.), Perspectives on the Philosophy of David K. Lewis, Oxford: Oxford University Press 2022: 23-40
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An overview of Lewis's metaphysics. I wrote most of the section on counterpart theory, and an appendix on counterpart-theoretic semantics for quantified modal logic
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I give a broadly Gricean explanation of various "free choice" phenomena, using ideas from dynamic semantics.
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Decision theory says that rational agents choose an option with maximal expected utility. But what are the options among which she chooses?
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I argue that the classical quantificational semantics of ability modals fails to account for a normatively central kind of ability, and suggest a minor tweak to fix the problem.
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I outline a physicalist explanation of why there appear to be irreducible phenomenal facts.
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A defense of sense-datum theory, an answer to the input problem for Jeffrey conditioning, and a solution to the hard problem of consciousness.
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I argue that none of the usual "interpretations of probability" provides a plausible account of probabilistic theories in science, and suggest an alternative.
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I outline an approach to semantics in which it makes sense to construe meanings as sets of possible worlds, and raise some questions about how we should understand the relevant space of worlds.D. Ball and B. Rabern (ed.), The Science of Meaning, Oxford: Oxford University Press 2018: 360--380
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I discuss recent triviality results for counterfactuals and different proposals for how to understand subjunctive conditional probability.
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I critically survey most norms that have been proposed for updating self-locating credences, and explain why such norms are needed.
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We argue (i) that impossible worlds are less useful to model fine-grained linguistic or mental content than often assumed, and (ii) that it is hard to find a notion of content that is neither too coarse-grained nor too fine-grained.
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I complete the update rule proposed in "Changing minds in a changing worlds" by extending it to cases of fission, and add some new arguments and clarifications.
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An advertisement for Best System Accounts of chance, disguised as a survey article.Alan H'ajek and Christopher Hitchcock (ed.), The Oxford Handbook of Probability and Philosophy, Oxford: Oxford University Press 2015: 423--439
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I analyse the paradox of the absentminded driver from different perspectives, and make a few general remarks about unstable decision problems, mixed strategies and the link between objective chance and rational credence.
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A critical overview of Lewis's philosophy of mind, with some general remarks on methodological issues.B. Loewer and J. Schaffer (ed.), A Companion to David Lewis, John Wiley & Sons 2015: 504--518
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An essay review of Michael Strevens's Tychomancy: Inferring probability from causal structure.
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I argue that there is no good evidence that Lewis ever endorsed a magnetic conception of meaning, and that his actual account of language reveals convincing arguments against it.
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I explain how various Humean accounts of chance, together with independently plausible constraints on rational belief, entail the Principal Principle.A. Wilson (ed.), Chance and Temporal Asymmetry, Oxford: Oxford University Press 2014: 81-99
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I present an extended counterpart-theoretic semantics for modal and temporal languages to account for paradoxes of occasional identity. Unlike in standard counterpart theory, Humphrey's counterpart at other worlds or times turns out to be none other than Humphrey himself.
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A review of arguments for and against the coherence of contingent identity.
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In some contexts, one might want to model the objects of knowledge, belief, probability, apriority or analyticity as sentences. However, this idea faces serious obstacles from mathematical logic.
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I propose a general rule for updating beliefs that takes into account both the impact of new evidence and changes in the subject's location.
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I defend a simple model theory for quantified modal and hybrid logics based on ideas from counterpart theory.G.~Russell and G.~Restall (ed.), New Waves in Philosophical Logic, Basingstoke: Palgrave MacMillan 2012: 8-29
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David Lewis: Metaphysik und Analyse (2009)A shallow and unbalanced book on Lewis's metaphysics, in German.Paderborn: mentis 2009
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I compare the old-fashioned view of metaphysics as an inquiry into broadly conceptual connections with the by now equally old-fashioned view of metaphysics as an inquiry into modal connections. I argue against proposals by Jackson and Lewis that the two projects ultimately coincide, and claim that we should prefer the conceptual project.Helen Bohse and Sven Walter (ed.), Philosophie: Grundlagen und Anwendungen. Ausgewahlte Beitrage aus den Sektionen der GAP 6, Paderborn: Mentis 2007: 520-528
Recent Blog Posts
Open Textbooks
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A philosophical introduction to decision theory, with digressions into Bayesian epistemology and value theory.
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An intermediate logic course centred around modal logic, with many philosophical applications.
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A gentle, but fast-paced introduction to computability theory and metalogic.
Current Teaching
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Mind, Matter, and Language
An introduction to philosophy of mind and philosophy of language for 2nd year students, co-taught with Milo Philips-Brown.
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Logic, Computability, and Incompleteness
Advanced logic, introducing central ideas and results from computability theory and metalogic, for 4th year students.
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Me, Myself, and Other (Less Important) Subjects
A course on self and self-location for 4th year students, co-taught with Mahrad Almotahari.
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Logic 2: Modal Logic
An intermediate logic course for 3rd year students centred around modal logic.
Programming
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Tree Proof Generator
A web page that tests formulas of first-order, propositional, or modal logic for validity and tries to output either a tableau proof or a countermodel.
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Philosophical Progress
Tracks new philosophy papers (and blog posts) from all over the internet.
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Lewis Search
Full-text search over the works of David Lewis.
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WebPPL-RSA
A WebPPL package for simulating rational speakers and hearers in the "Rational Speech Act" framework.