John MacFarlane

"Philosophical logic" describes two distinct areas: the investigation of the fundamental concepts of logic, the formal investigation of alternatives and extensions to classical logic. The first is a philosophical discipline, concerned with notions like truth, propositions, necessity, logical consequence, vagueness, and reasoning. The second is a technical discipline, devoted to developing formal logical systems-modal logics, second-order logics, intuitionistic logics, relevance logics, logics of vagueness and conditionals-and proving things about them. Most texts in philosophical logic focus on one of these areas, but in this book John MacFarlane treats them together in an integrated way, showing how philosophical considerations motivate the technical projects, and how the constraints revealed by the technical projects illuminate the philosophical issues. Topics covered include quantifiers, modal logic, indicative conditionals, model-theoretic and proof-theoretic characterizations of logical consequence, intuitionistic logic, fundamental logical disagreement, relevance logic, the relation of logic and reasoning, and vagueness. Each chapter is organized around suggested readings and includes exercises. Key Features: An integrated treatment of the technical and philosophical issues comprising philosophical logic Written by a leading authority on logicism and logical form and a successful expositor and teacher Designed to serve students taking only one course in logic beyond the introductory level Provides tools and concepts necessary to understand work in many areas of analytic philosophy Includes exercises, suggested readings, and suggestions for further exploration in each chapter.

The central chapter of Burnyeat’s Map is organized like a commentary, moving through Metaphysics Ζ (and parts of Η) section by section. But unlike a commentary, it does not strive for comprehensiveness. Its aim is to describe the general lay of the land—what is being argued for where, in what way, and why— and so its exegesis is limited to Aristotle’s “signposts.” For example, every time Aristotle says “we must investigate” or “as we have seen,” Burnyeat asks “where?” As far as possible, he tries to construct his map on philological evidence, remaining neutral on many of the substantive issues that have defined readings of Ζ. The hope is that, map in hand, we can interpret Ζ’s notoriously obscure arguments with a better sense of their place in Aristotle’s overall project.

On Schiffer’s new view, propositions are easy to come by. Any that-clause can be counted on to express one. Thus, trivially, there are vague propositions, conditional propositions, moral and aesthetic propositions. And where propositions go, truth and falsity follow: barring paradoxical cases, Schiffer accepts instances of the schemata “the proposition that p is true iff p” and “the proposition that p is false iff not-p.” What isn’t easy to find, Schiffer thinks, is determinate truth. By the end of the book, we have heard that a huge number of the things we say or think are indeterminate in truth value: not just whether Schiffer’s book is long, but whether the property of being in pain is identical with any physical property, whether torturing children for fun is morally permissible, whether modus ponens is a valid inference rule, and whether someone else would have shot Kennedy if Oswald hadn’t. Indeed, on Schiffer’s view, there are no determinately true moral propositions and virtually no determinately true conditionals that are “likely to interest us”.

Let me start with a well-known story. Kant held that logic and conceptual analysis alone cannot account for our knowledge of arithmetic: “however we might turn and twist our concepts, we could never, by the mere analysis of them, and without the aid of intuition, discover what is the sum [7+5]” (KrV, B16). Frege took himself to have shown that Kant was wrong about this. According to Frege’s logicist thesis, every arithmetical concept can be defined in purely logical terms, and every theorem of arithmetic can be proved using only the basic laws of logic. Hence, Kant was wrong to think that our grasp of arithmetical concepts and our knowledge of arithmetical truth depend on an extralogical source—the pure intuition of time (Frege 1884, §89, §109). Arithmetic, properly understood, is just a part of logic.

Logic is usually thought to concern itself only with features that sentences and arguments possess in virtue of their logical structures or forms. The logical form of a sentence or argument is determined by its syntactic or semantic structure and by the placement of certain expressions called “logical constants.”[1] Thus, for example, the sentences Every boy loves some girl. and Some boy loves every girl. are thought to differ in logical form, even though they share a common syntactic and semantic structure, because they differ in the placement of the logical constants “every” and “some”. By contrast, the sentences Every girl loves some boy. and Every boy loves some girl. are thought to have the same logical form, because “girl” and “boy” are not logical constants. Thus, in order to settle questions about logical form, and ultimately about which arguments are logically valid and which sentences logically true, we must distinguish the “logical constants” of a language from its nonlogical expressions

Much of The Reason’s Proper Study is devoted to defending the claim that simply by stipulating an abstraction principle for the “number-of” functor, we can simultaneously fix a meaning for this functor and acquire epistemic entitlement to the stipulated principle. In this paper, I argue that the semantic and epistemological principles Hale and Wright offer in defense of this claim may be too strong for their purposes. For if these principles are correct, it is hard to see why they do not justify platonist strategies that are not in any way “neo-Fregean,” e.g. strategies that treat “the number of Fs” as a Russellian definite description rather than a singular term, or employ axioms that do not have the form of abstraction principles.

According to Semantic Minimalism, every use of "Chiara is tall" (fixing the girl and the time) semantically expresses the same proposition, the proposition that Chiara is (just plain) tall. Given standard assumptions, this proposition ought to have an intension (a function from possible worlds to truth values). However, speakers tend to reject questions that presuppose that it does. I suggest that semantic minimalists might address this problem by adopting a form of "nonindexical contextualism," according to which the proposition invariantly expressed by "Chiara is tall" does not have a context-invariant intension. Nonindexical contextualism provides an elegant explanation of what is wrong with "context-shifting arguments" and can be seen as a synthesis of the (partial) insights of semantic minimalists and radical contextualists.

One of the central themes of Brandom’s work is that we should construct our sematic theories around material validity and incompatibility, rather than reference, truth, and satisfaction. This approach to semantics is motivated in part by Brandom’s pragmatism about the relation between semantics and the more general study of language use—what he calls “pragmatics”: Inferring is a kind of doing. . . . The status of inference as something that can be done accordingly holds out the promise of securing an appropriate relation between pragmatics, the study of the practices, and semantics, the study of the corresponding contents. (MIE, 91)1 Although Brandom does not go so far as to say that a pragmatist attitude to the relation between semantics and pragmatics requires an inferentialist semantics, his motivating arguments strongly suggest that a pragmatist ought to be an inferentialist. In what follows, I discuss the connections between Brandom’s pragmatism and his inferentialism. I’ll argue that pragmatism, as Brandom initially describes it—the view that “semantics must answer to pragmatics”—does not favor an inferentialist approach to semantics over a truth-conditional one. I’ll then consider whether inferentialism might be..

It is taken for granted in much of the literature on vagueness that semantic and epistemic approaches to vagueness are fundamentally at odds. If we can analyze borderline cases and the sorites paradox in terms of degrees of truth, then we don’t need an epistemic explanation. Conversely, if an epistemic explanation suffices, then there is no reason to depart from the familiar simplicity of classical bivalent semantics. I question this assumption, showing that there is an intelligible motivation for adopting a many-valued semantics even if one accepts a form of epistemicism. The resulting hybrid view has advantages over both classical epistemicism and traditional many-valued approaches.

In Confusion: A Study in the Theory of Knowledge, Joseph Camp argues that the reasoning of a person who has confused two objects in her thought and talk ought to be appraised using a four-valued relevance logic. I discuss two key moves in Camp’s argument: the assumption that charity to the reasoner requires recognition of her arguments as valid, and the argument that validity for a truth-valueless discourse should not be defined in terms of truth preservation. I then question whether Camp’s four-valued semantics satisfies his own desiderata for a logic of confusion.

In recent work, John McDowell has urged that we resurrect the Kantian thesis that concepts without intuitions are empty. I distinguish two forms of the thesis: a strong form that applies to all concepts and a weak form that is limited to empirical concepts. Because McDowell rejects Kant’s philosophy of mathematics, he can accept only the weaker form of the thesis. But this position is unstable. The reasoning behind McDowell’s insistence that empirical concepts can have content only if they are actualizable in passive experience makes it mysterious how the concepts of pure mathematics can have content. In fact, historically, it was anxiety about the possibility of mathematical content, and not worries about the “Myth of the Given,” that spurred the retreat from Kantian views of empirical content. McDowell owes us some more therapy on this score.

By “epistemic modals,” I mean epistemic uses of modal words: adverbs like “necessarily,” “possibly,” and “probably,” adjectives like “necessary,” “possible,” and “probable,” and auxiliaries like “might,” “may,” “must,” and “could.” It is hard to say exactly what makes a word modal, or what makes a use of a modal epistemic, without begging the questions that will be our concern below, but some examples should get the idea across. If I say “Goldbach’s conjecture might be true, and it might be false,” I am not endorsing the Cartesian view that God could have made the truths of arithmetic come out differently. I make the claim not because I believe in the metaphysical contingency of mathematics, but because I know that Goldbach’s conjecture has not yet been proved or refuted. Similarly, if I say “Joe can’t be running,” I am not saying that Joe’s constitution prohibits him from running, or that Joe is essentially a non-runner, or that Joe isn’t allowed to run. My basis for making the claim may be nothing more than that I see Joe’s running shoes hanging on a hook.

In lieu of an abstract, here is a brief excerpt of the content:Journal of the History of Philosophy 39.3 (2001) 454-456 [Access article in PDF] Michael Potter. Reason's Nearest Kin: Philosophies of Arithmetic from Kant to Carnap.New York: Oxford University Press, 2000. Pp. x + 305. Cloth, $45.00. This book tells the story of a remarkable series of answers to two related questions:(1) How can arithmetic be necessary and knowable a priori? [End Page 454](2) What accounts for the applicability of arithmetic to matters of empirical fact?These are philosophical questions, part of a "wider puzzle of explaining the link between experience, language, thought, and the world" (18). But answers to them are heavily constrained by technical results in logic and mathematics, and most of Potter's protagonists are either mathematicians (Frege, Dedekind, Ramsey, Hilbert, Gödel) or mathematically trained philosophers (Kant, Russell, Carnap). (Only Wittgenstein fits neither category.) Potter, whose doctorate was in pure mathematics, is an able guide.It is not hard to think of answers to these questions taken singly; what is hard is answering both at the same time. Formalists can easily explain why arithmetic does not depend for its justification on empirical fact—it is just a game with symbols, not responsible to anything beyond its own rules—but they then have trouble explaining why the world of empirical fact is constrained by this game. Empiricists can explain the applicability of arithmetic in just the same way they explain the applicability of physics, but they then must then explain away the apparent a prioricity and necessity of arithmetic. Kant was the first to propose a plausible answer to both questions: arithmetic is both necessary and empirically applicable because it is grounded in the spatio-temporal form of any possible experience.What unites Frege, Dedekind, Russell, Ramsey, Hilbert, and Carnap is that they reject Kant's answer while continuing to seek an answer to his question: how can arithmetic's necessity be reconciled with its applicability? Potter helpfully classifies their projects by the surrogates they substitute for Kant's appeal to the form of spatio-temporal intuition: Frege and Dedekind appeal to thought, Russell to necessary features of the world, Wittgenstein, Ramsey, and Carnap to language, and Hilbert to the necessary structure of our experience of finitary combinations of objects. (Revealingly, the logicists are not grouped together in Potter's taxonomy.) A chapter (or two) is devoted to each of these thinkers, plus Kant and Gödel.This breadth of coverage does not come at the price of superficiality: Potter's chapters are (by and large) accurate, penetrating, and full of interesting insights. I cannot think of another book that offers such clear explanations of the many mathematical concepts and distinctions one must grasp in order to follow debates in the philosophy of arithmetic. The Russell chapters are enhanced by numerous quotations from archival material. The exposition of Hilbert's programme and the implications for it of Gödel's theorems is the best I have seen. The discussions of Wittgenstein's views on arithmetic and of Carnap's syntactical approach also shine. The chapters on Kant and Frege are somewhat weaker; the discussion of Kant, in particular, would have benefited from some engagement with Michael Friedman's views.But the real contribution of Potter's book is its integration of these nine thinkers into a single coherent story. No one will be surprised that Russell's motivations can only be understood in light of Frege's failures, or that many features of Wittgenstein's cryptic work become clearer when seen in light of the specific problems with Russell's system. But there are also some less obvious payoffs: for example, Hilbert's programme is usefully compared with Russell's regressive method (227-8), and Carnap and Russell are shown to face a common dilemma (269, 286).If there is a central theme to Potter's story, it is "how often we have had to reject an [End Page 455] account not for philosophical reasons but for technical ones" (278). Frege's program founders on Russell's paradox, Russell's...

Much philosophy of logic is shaped, explicitly or implicitly, by the thought that logic is distinctively formal and abstracts from material content. The distinction between formal and material does not appear to coincide with the more familiar contrasts between a priori and empirical, necessary and contingent, analytic and synthetic—indeed, it is often invoked to explain these. Nor, it turns out, can it be explained by appeal to schematic inference patterns, syntactic rules, or grammar. What does it mean, then, to say that logic is distinctively formal?

We consider a paradox involving indicative conditionals (‘ifs’) and deontic modals (‘oughts’). After considering and rejecting several standard options for resolv- ing the paradox—including rejecting various premises, positing an ambiguity or hidden contextual sensitivity, and positing a non-obvious logical form—we offer a semantics for deontic modals and indicative conditionals that resolves the paradox by making modus ponens invalid. We argue that this is a result to be welcomed on independent grounds, and we show that rejecting the general validity of modus ponens is compatible with vindicating most ordinary uses of modus ponens in reasoning.

Recent years have seen an explosion of interest in the semantics of knowledge-attributing sentences, not just among epistemologists but among philosophers of language seeking a general understanding of linguistic context sensitivity. Despite all this critical attention, however, we are as far from consensus as ever. If we have learned anything, it is that each of the standard views—invariantism, contextualism, and sensitive invariantism—has its Achilles’ heel: a residuum of facts about our use of knowledge attributions that it can explain only with special pleading. This is not surprising if, as I will argue, there is a grain of truth in each of these views.

According to “sensitive invariantism,” the word “know” expresses the same relation in every context of use, but what it takes to stand in this relation to a proposition can vary with the subject’s circumstances. Sensitive invariantism looks like an attractive reconciliation of invariantism and contextualism. However, it is incompatible with a widely-held view about the way knowledge is transmitted through testimony. If both views were true, someone whose evidence for p fell short of what was required for knowledge in her circumstances could come to know that p simply by feeding her evidence to someone in less demanding circumstances and then accepting his testimony.

This is a lightly edited version of my comments on Brandom’s Lecture 2, as delivered in Prague at the “Prague Locke Lectures” in April, 2007. I try to say why Brandom’s proposed demarcation is significant, by placing it in a broader context of demarcation proposals from Kant to the twentieth century. I then raise some questions about the basic ingredients of Brandom’s demarcation—the notions of PP-sufficiency and VP-sufficiency—and question whether the vocabulary of conditionals, Brandom’s paradigm for logical vocabulary, can be universal-LX.

To assert something is to perform a certain kind of act. This act is different in kind both from other speech acts, like questions, requests, commands, promises, and apologies, and from acts that are not speech acts, like toast buttering and inarticulate yodeling. My question, then is this: what features of an act qualify it as an assertion, and not one of these other kinds of act? To focus on a particular example: in uttering “Bill will close the window,” one might be practicing English pronunciation, asserting that Bill will close the window, or requesting that Bill close the window. What makes it the case that one is doing one of these and not another?