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I recently noticed that over the last day or so I’d got increased traffic to this rarely-visited website. Quite a few folks were reaching the home page, and a surprising number were landing on an old post of mine from 2004 about Haskell. Why on earth did that happen? Well, on August 2, John MacFarlane posted a 20 year retrospective on his much-used document conversion toolkit, pandoc. In telling the tale, John mentioned that he got turned on to Haskell back in 2004/5 because that old post of…

This is an intensive class on logical bilateralism, taught by Sara Ayhan and me at esslli 2026. Logical bilateralism is an approach to meaning and consequence that foregrounds a symmetry between certain notions, like assertion and denial, proof and refutation or truth and falsity. Bilateralist approaches to such dual distinctions take both sides as primitive rather than—as in conventional ‘unilateralist’ approaches—taking one notion to be fundamental and defining the other in its terms. In…

Abstract: Graham Priest’s simple three-valued logic LP has many curious properties. It has the same valid formulas as classical logic, but differs from classical logic when it comes to valid sequents. The valid sequents do not uniquely characterise the logic: it is possible to have more than one different LP-“negation”, each of which satisfies all the LP-requirements, without being equivalent. (The situation is not unlike modal operators in your favoured modal logic. A modal logic like S5 does…

Abstract: In this talk I will introduce a simple hypersequent calculus for the propositional modal logic S5, explaining how this representation encodes a natural form of reasoning about possibility and necessity. I then explain how the familiar structural rules of contraction and weakening take two forms in such a hypersequent calculus: they operate inside sequents, as familiar in substructural logics (linear logic, relevant logics, affine logic, etc.), but they also take an outer form,…

Abstract: Graham Priest’s simple three-valued logic LP has many curious properties. It has the same valid formulas as classical logic, but differs from classical logic when it comes to valid sequents. The valid sequents do not uniquely characterise the logic: it is possible to have more than one different LP-“negation”, each of which satisfies all the LP-requirements, without being equivalent. (The situation is not unlike modal operators in your favoured modal logic. A modal logic like S5 does…

Abstract: Graham Priest’s simple three-valued logic LP has many curious properties. It has the same valid formulas as classical logic, but differs from classical logic when it comes to valid sequents. The valid sequents do not uniquely characterise the logic: it is possible to have more than one different LP-“negation”, each of which satisfies all the LP-requirements, without being equivalent. (The situation is not unlike modal operators in your favoured modal logic. A modal logic like S5 does…

Abstract: In this talk I will introduce a simple hypersequent calculus for the propositional modal logic S5, explaining how this representation encodes a natural form of reasoning about possibility and necessity. I then explain how the familiar structural rules of contraction and weakening take two forms in such a hypersequent calculus: they operate inside sequents, as familiar in substructural logics (linear logic, relevant logics, affine logic, etc.), but they also take an outer form,…

This Easter season, my church marked the occasion with an art exhibition on the theme of Betrayal, and some short reflective evening services on Maundy Thursday, Good Friday, and Holy Saturday. For the Saturday service, I was asked to give a short reflection on the gospel text: John 19:31-42. Christ in the Tomb, by Mihály Munkácsy (1881) Since I have a website and somewhere to archive my presentations, I’ve uploaded the text of the reflection here.