My first major research project was on the rationality of group decisions, focusing on the claimed importance of common knowledge. I developed a new argument that people never have common knowledge, showed how common knowledge is not required for rational coordination, and described how implausibly strong assumptions about common knowledge are key to the famous agreement theorem.
While working on this project, I became dissatisfied with the representation of beliefs and preferences in standard formal models of decision-making, and wanted to do better. I first approached this question through a paper on models of awareness in economic theory. This inspired a second project on the nature of propositional attitudes and their contents (with papers on the consistency of structured propositions, and on the consequences of rejecting Leibniz's Law). I also wrote a series of papers on the semantics of propositional attitude reports, with particular attention to logical omniscience, Frege's puzzle, and the connection between them (I've developed versions of Russellianism, Fregeanism, and a third option with elements of each).
Recently, I have returned to questions about the explanation of action, both in human and artificial agents. A recent paper with Ben Holguín aims to re-instate trying as a central notion in the theory of action. A paper with Kyle Mahowald asks whether modern LLMs can produce meaningful text. The second half of this paper addresses whether LLMs should be considered to have propositional attitudes, and how this relates to our understanding of LLM behavior.
I have also returned to questions in decision theory, with a pair of papers on the rationality of incomplete preferences: one focusing on philosophical questions about the rationality of such preferences; the other focusing on relevant mathematical results. This last project has inspired a new stream of work in the theory of value. Christian Tarsney, Dean Spears and I developed extensions of my earlier decision-theoretic work to the ethics of population and distribution, and (in a completely different direction), Robbie Kubala, Adam Lovett and I have written about the value of irreplaceable works of art.
I am currently working on a new interpretation of the moral metaphysics of the great Ming dynasty philosopher Wang Yangming (1472-1529), in particular his slogan "mind is principle" (心即理). This last paper grows out of a longstanding interest in Wang's philosophy, including papers on his moral psychology, moral epistemology, and more broadly, on his doctrine of the "unity of knowledge and action".
In the past, I have also worked on interpersonal well-being comparisons (and a related version of Arrow's theorem), on non-classical and modal set theories, and on a notion of ontological dependence Aristotle develops in his discussions of blood and of time. In another life, I wrote a paper on DNA computing (and contributed to a second).