
177Necessitists about set theory think that the pure sets exists, and are the way they are, as a matter of necessity. They cannot explain why the sets (de rebus) are all the sets. This constitutes the UrObjection against necessitism; it is the primary motivation cited by potentialists about set theory. At least three families of potentialism draw motivation from the UrObjection. Contingentists think that any things could form a set even if they actually did not. Prioritists think that sets hyper…Read more

Wittgenstein on Solipsism in the 1930s: Private Pains, Private Languages, and Two Uses of 'I'In Anthony O'Hear (ed.), Metaphysics, Cambridge University Press. 2018.

925Wand/Set Theories: A realization of Conway's mathematicians' liberation movement, with an application to Church's set theory with a universal setJournal of Symbolic Logic. forthcoming.Consider a variant of the usual story about the iterative conception of sets. As usual, at every stage, you find all the (bland) sets of objects which you found earlier. But you also find the result of tapping any earlierfound object with any magic wand (from a given stock of magic wands). By varying the number and behaviour of the wands, we can flesh out this idea in many different ways. This paper's main Theorem is that any loosely constructive way of fleshing out this idea is synonymous with…Read more

682The iterative conception of function and the iterative conception of setIn Carolin Antos, Neil Barton & Giorgio Venturi (eds.), The Palgrave Companion to the Philosophy of Set Theory, Palgrave. 2023.Hilary Putnam once suggested that “the actual existence of sets as ‘intangible objects’ suffers… from a generalization of a problem first pointed out by Paul Benacerraf… are sets a kind of function or are functions a sort of set?” Sadly, he did not elaborate; my aim, here, is to do so on his behalf. There are wellknown methods for treating sets as functions and functions as sets. But these do not raise any obvious philosophical or foundational puzzles. For that, we first need to provide a full…Read more

636We offer two arguments against the halving repose to Sleeping Beauty. First, we show that halving violates the Epistemological SureThing Principle, which we argue is a necessary constraint on any reasonable probability assignment. The constraint is that if hypothetically on C you assign to A the same probability you assign to A hypothetical on notC, you must assign that probability to A simpliciter. Epistemically, it's a sure thing for you that A has this probability. Second, we show that halv…Read more

353Naturalism, Realism, and Normativity, by Hilary Putnam, edited by Mario de Caro (review)Philosophy 92 (2): 30515. 2017.Hilary Putnam’s Realism with a Human Face began with a quotation from Rilke, exhorting us to ‘try to love the questions themselves like locked rooms and like books that are written in a very foreign tongue’. Putnam followed this advice throughout his life. His love for the questions permanently changed how we understand them. In Naturalism, Realism, and Normativity – published only a few weeks after his death – Putnam continued to explore central questions concerning realism and perception, from…Read more

282Other minds and God: Russell and Stout on James and SchillerIn Sarin Marchetti & Maria Baghramian (eds.), Pragmatism and the European Traditions: Encounters with Analytic Philosophy and Phenomenology Before the Great Divide, Routledge. pp. 86109. 2017.In 1907–8, Russell and Stout presented an objection against James and Schiller, to which both James and Schiller replied. In this paper, I shall revisit their transatlantic exchange. Doing so will yield a better understanding of Schiller’s relationship to a worryingly solipsistic brand of phenomenalism. It will also allow us to appreciate a crucial difference between Schiller and James; a difference which James explicitly downplayed.

198Review of: Ontology After Carnap, by Stephan Blatti and Sandra Lapointe (eds.) (review)Notre Dame Philosophical Reviews. 2016.Ontology after Carnap focusses on metaontology in the light of recent interest in Carnap’s ‘Empiricism, Semantics and Ontology’. That paper is at the centre of things, as it is where Carnap formulates his internal/external dichotomy. If you haven’t already encountered the dichotomy, then neither Ontology after Carnap, nor this review, is for you. My aim in this review is to try to tease out some of the book’s themes, thereby giving some sense of contemporary neoCarnapianism.

549Realistic structuralism's identity crisis: A hybrid solutionAnalysis 66 (3). 2006.Keränen (2001) raises an argument against realistic (ante rem) structuralism: where a mathematical structure has a nontrivial automorphism, distinct indiscernible positions within the structure cannot be shown to be nonidentical using only the properties and relations of that structure. Ladyman (2005) responds by allowing our identity criterion to include 'irreflexive twoplace relations'. I note that this does not solve the problem for structures with indistinguishable positions, i.e. positio…Read more

757A fictionalist theory of universalsIn Peter Fritz & Nicholas K. Jones (eds.), HigherOrder Metaphysics, Oxford University Press. 2024.Universals are putative objects like wisdom, morality, redness, etc. Although we believe in properties (which, we argue, are not a kind of object), we do not believe in universals. However, a number of ordinary, natural language constructions seem to commit us to their existence. In this paper, we provide a fictionalist theory of universals, which allows us to speak as if universals existed, whilst denying that any really do.

588Symmetric relations, symmetric theories, and PythagrapheanismPhilosophy and Phenomenological Research (3): 583612. 2022.It is a metaphysical orthodoxy that interesting nonsymmetric relations cannot be reduced to symmetric ones. This orthodoxy is wrong. I show this by exploring the expressive power of symmetric theories, i.e. theories which use only symmetric predicates. Such theories are powerful enough to raise the possibility of Pythagrapheanism, i.e. the possibility that the world is just a vast, unlabelled, undirected graph.

200An open source open access logic textbook

663Mathematical Internal RealismIn Sanjit Chakraborty & James Ferguson Conant (eds.), Engaging Putnam, De Gruyter. pp. 157182. 2022.In “Models and Reality” (1980), Putnam sketched a version of his internal realism as it might arise in the philosophy of mathematics. Here, I will develop that sketch. By combining Putnam’s modeltheoretic arguments with Dummett’s reflections on Gödelian incompleteness, we arrive at (what I call) the SkolemGödel Antinomy. In brief: our mathematical concepts are perfectly precise; however, these perfectly precise mathematical concepts are manifested and acquired via a formal theory, which is und…Read more

701Against Cumulative Type TheoryReview of Symbolic Logic 15 (4): 90749. 2022.Standard Type Theory, STT, tells us that b^n(a^m) is wellformed iff n=m+1. However, Linnebo and Rayo have advocated the use of Cumulative Type Theory, CTT, has more relaxed typerestrictions: according to CTT, b^β(a^α) is wellformed iff β > α. In this paper, we set ourselves against CTT. We begin our case by arguing against Linnebo and Rayo’s claim that CTT sheds new philosophical light on set theory. We then argue that, while CTT ’s typerestrictions are unjustifiable, the typerestrictions i…Read more

599Level theory, part 1: Axiomatizing the bare idea of a cumulative hierarchy of setsBulletin of Symbolic Logic 27 (4): 436460. 2021.The following barebones story introduces the idea of a cumulative hierarchy of pure sets: 'Sets are arranged in stages. Every set is found at some stage. At any stage S: for any sets found before S, we find a set whose members are exactly those sets. We find nothing else at S.' Surprisingly, this story already guarantees that the sets are arranged in wellordered levels, and suffices for quasicategoricity. I show this by presenting Level Theory, a simplification of set theories due to Scott, M…Read more

416Level Theory, Part 2: Axiomatizing the Bare Idea of a Potential HierarchyBulletin of Symbolic Logic 27 (4): 461484. 2021.Potentialists think that the concept of set is importantly modal. Using tensed language as an heuristic, the following barbones story introduces the idea of a potential hierarchy of sets: 'Always: for any sets that existed, there is a set whose members are exactly those sets; there are no other sets.' Surprisingly, this story already guarantees wellfoundedness and persistence. Moreover, if we assume that time is linear, the ensuing modal set theory is almost definitionally equivalent with non…Read more

422Level Theory, Part 3: A Boolean Algebra of Sets Arranged in WellOrdered LevelsBulletin of Symbolic Logic 28 (1): 126. 2022.On a very natural conception of sets, every set has an absolute complement. The ordinary cumulative hierarchy dismisses this idea outright. But we can rectify this, whilst retaining classical logic. Indeed, we can develop a boolean algebra of sets arranged in wellordered levels. I show this by presenting Boolean Level Theory, which fuses ordinary Level Theory (from Part 1) with ideas due to Thomas Forster, Alonzo Church, and Urs Oswald. BLT neatly implement Conway’s games and surreal numbers; a…Read more

89Forall x: Dortmund (2nd ed.). 2021.forall x: Dortmund is an adaptation and German translation of forall x: Calgary. As such, it is a fullfeatured textbook on formal logic. It covers key notions of logic such as consequence and validity, the syntax of truthfunctional (propositional) logic and truthtable semantics, the syntax of firstorder (predicate) logic with identity and firstorder interpretations, formalizing German in TFL and FOL, and Fitchstyle natural deduction proof systems for both TFL and FOL. It also deals with so…Read more

2536Para Todxs: Natal  uma introdução à lógica formalPPGFILUFRN. 2022.Livrotexto de introdução à lógica, com (mais do que) pitadas de filosofia da lógica, produzido como uma versão revista e ampliada do livro Forallx: Calgary. Tratase da versão de 13 de outubro de 2022. Comentários, críticas, correções e sugestões são muito bemvindos.

362Review of: Hilary Putnam on Logic and Mathematics, by Geoffrey Hellman and Roy T. Cook (eds.) (review)Mind 129 (516): 13271337. 2019.Putnam’s most famous contribution to mathematical logic was his role in investigating Hilbert’s Tenth Problem; Putnam is the ‘P’ in the MRDP Theorem. This volume, though, focusses mostly on Putnam’s work on the philosophy of logic and mathematics. It is a somewhat bumpy ride. Of the twelve papers, two scarcely mention Putnam. Three others focus primarily on Putnam’s ‘Mathematics without foundations’ (1967), but with no interplay between them. The remaining seven papers apparently tackle unrelate…Read more

628The Philosophical Significance of Tennenbaum’s TheoremPhilosophia Mathematica 20 (1): 114121. 2012.Tennenbaum's Theorem yields an elegant characterisation of the standard model of arithmetic. Several authors have recently claimed that this result has important philosophical consequences: in particular, it offers us a way of responding to modeltheoretic worries about how we manage to grasp the standard model. We disagree. If there ever was such a problem about how we come to grasp the standard model, then Tennenbaum's Theorem does not help. We show this by examining a parallel argument, from …Read more

352Review of: Reading Putnam, by Maria Baghramian (ed.) (review)Mind 123 (490): 569575. 2014.Reading Putnam consists largely of papers from the fantastic ‘Putnam @80’ conference (organised by Maria Baghramian in 2007) together with replies from Hilary Putnam. Given the diversity of Putnam’s work, the papers in this collection cover many different topics. This makes the collection difficulty to read but, ultimately, extremely rewarding. In this review, I focus on the contributions from Michael Devitt, Charles Parsons, Richard Boyd, Ned Block, Charles Travis and John McDowell, together wi…Read more

748Structure and Categoricity: Determinacy of Reference and Truth Value in the Philosophy of MathematicsPhilosophia Mathematica 24 (3): 283307. 2016.This article surveys recent literature by Parsons, McGee, Shapiro and others on the significance of categoricity arguments in the philosophy of mathematics. After discussing whether categoricity arguments are sufficient to secure reference to mathematical structures up to isomorphism, we assess what exactly is achieved by recent ‘internal’ renditions of the famous categoricity arguments for arithmetic and set theory.

3241Forall x: Calgary. An Introduction to Formal Logic (4th ed.)Open Logic Project. 2023.forall x: Calgary is a fullfeatured textbook on formal logic. It covers key notions of logic such as consequence and validity of arguments, the syntax of truthfunctional propositional logic TFL and truthtable semantics, the syntax of firstorder (predicate) logic FOL with identity (firstorder interpretations), symbolizing English in TFL and FOL, and Fitchstyle natural deduction proof systems for both TFL and FOL. It also deals with some advanced topics such as modal logic, soundness, and fu…Read more

547Wittgenstein on Solipsism in the 1930s: Private Pains, Private Languages, and Two Uses of ‘I’Royal Institute of Philosophy Supplement 82 205229. 2018.In the earlytomid 1930s, Wittgenstein investigated solipsism via the philosophy of language. In this paper, I want to reopen Wittgenstein's ‘grammatical’ examination of solipsism.Wittgenstein begins by considering the thesis that only I can feel my pains. Whilst this thesis may tempt us towards solipsism, Wittgenstein points out that this temptation rests on a grammatical confusion concerning the phrase ‘my pains’. In Section 1, I unpack and vindicate his thinking. After discussing ‘my pains’,…Read more

386Grades of Discrimination: Indiscernibility, Symmetry, and RelativityNotre Dame Journal of Formal Logic 58 (4): 527553. 2017.There are several relations which may fall short of genuine identity, but which behave like identity in important respects. Such grades of discrimination have recently been the subject of much philosophical and technical discussion. This paper aims to complete their technical investigation. Grades of indiscernibility are defined in terms of satisfaction of certain firstorder formulas. Grades of symmetry are defined in terms of symmetries on a structure. Both of these families of grades of discr…Read more

107Philosophy and Model TheoryOxford University Press. 2018.Philosophy and model theory frequently meet one another. Philosophy and Model Theory aims to understand their interactions Model theory is used in every ‘theoretical’ branch of analytic philosophy: in philosophy of mathematics, in philosophy of science, in philosophy of language, in philosophical logic, and in metaphysics. But these wideranging appeals to model theory have created a highly fragmented literature. On the one hand, many philosophically significant mathematical results are found on…Read more

477The Weight of Truth: Lessons for Minimalists from Russell's Gray's Elegy ArgumentProceedings of the Aristotelian Society 114 (3pt3): 261289. 2014.Minimalists, such as Paul Horwich, claim that the notions of truth, reference and satisfaction are exhausted by some very simple schemes. Unfortunately, there are subtle difficulties with treating these as schemes, in the ordinary sense. So instead, minimalists regard them as illustrating oneplace functions, into which we can input propositions (when considering truth) or propositional constituents (when considering reference and satisfaction). However, Bertrand Russell's Gray's Elegy argument …Read more

497Knot and Tonk: Nasty Connectives on ManyValued TruthTables for Classical Sentential LogicAnalysis 76 (1): 719. 2016.Prior’s Tonk is a famously horrible connective. It is defined by its inference rules. My aim in this article is to compare Tonk with some hitherto unnoticed nasty connectives, which are defined in semantic terms. I first use manyvalued truthtables for classical sentential logic to define a nasty connective, Knot. I then argue that we should refuse to add Knot to our language. And I show that this reverses the standard dialectic surrounding Tonk, and yields a novel solution to the problem of ma…Read more

260Hyperloops do not threaten the notion of an effective procedureLecture Notes in Computer Science 5635 6878. 2009.This paper develops my (BJPS 2009) criticisms of the philosophical significance of a certain sort of infinitary computational process, a hyperloop. I start by considering whether hyperloops suggest that "effectively computable" is vague (in some sense). I then consider and criticise two arguments by Hogarth, who maintains that hyperloops undermine the very idea of effective computability. I conclude that hyperloops, on their own, cannot threaten the notion of an effective procedure.
Areas of Specialization
Logic and Philosophy of Logic 
Philosophy of Mathematics 
Metaphysics 
Metaphilosophy 
Philosophy of Language 
Areas of Interest
HigherOrder Logic 
Methodology in Metaphysics 
Set Theory as a Foundation 