Second-Order Logic

Here's the thing: when you look at it from just the right angle, it's entirely obvious how semantics for second-order relevant logics ought to go. Or at least, if you've understood how semantics for first-order relevant logics ought to go, there are perspectives like this. What's more is that from any such angle, the metatheory that needs doing can be summed up in one line: everything is just as in the first-order case, but with more indices. Of course, it's no (...) small matter finding the magical angle from which everything becomes obvious. And even having found this perspective, one cannot assume one's audience will find things as obvious as oneself. All that to say this: if the results in the paper below strike you as obvious, pay attention to the perspective that makes that possible. And if they don't, feel free to ignore this preamble in its entirety. (shrink)

Abstractionism in the philosophy of mathematics aims at deriving large fragments of mathematics by combining abstraction principles (i.e. the abstract objects $\S e_1, \S e_2$, are identical if, and only if, an equivalence relation $Eq_\S$ holds between the entities $e_1, e_2$) with logic. Still, as highlighted in work on the semantics for relevant logics, there are different ways theories might be combined. In exactly what ways must logic and abstraction be combined in order to get interesting mathematics? In this paper, (...) we investigate the matter by deriving the axioms of second-order Peano Arithmetic from Frege's Basic Law V (the extension of $F$ is identical with the extension of $G$ if, and only if, $F$ and $G$ are extensionally equivalent) in the presence of a relevant higher-order logic. The results are interesting. Not only must we take on logic as true, and not only must we apply our logic to abstraction principles, but also we have to apply our theory of abstraction back to the logic in order to arrive at arithmetic. Thus, what Abstractionism gives us is not simply what we get from abstraction via logic, but also what we get from logic via abstraction. (shrink)

Neo-logicists have claimed that Hume's Principle (HP) may be taken as a stipulative definition of cardinal number. This claim is threatened by the fact that HP is not conservative over pure second-order logic. I argue that the dominant neo-logicist response to the conservativeness objection is not satisfactory. Then I propose a novel version of neo-logicism, based on Heck's Two-sorted Hume's Principle (2HP), which does meet the conservativeness objection—provided that conservativeness is understood semantically and not deductively. I also argue that on (...) my proposal, the Bad Company problem is solved by conservativeness. (shrink)

This chapter explores the metaphysical views about higher-order logic held by two individuals responsible for introducing it to philosophy: Gottlob Frege (1848–1925) and Bertrand Russell (1872–1970). Frege understood a function at first as the remainder of the content of a proposition when one component was taken out or seen as replaceable by others, and later as a mapping between objects. His logic employed second-order quantifiers ranging over such functions, and he saw a deep division in nature between objects and functions. (...) Russell understood propositional functions as what is obtained when constituents of propositions are replaced by variables, but eventually denied that they were entities in their own right. Both encountered contradictions when supposing there to exist as many objects as functions, and both adopted views about the meaningfulness of higher-order discourse that were difficult to state from within their own strictures. (shrink)

In the language of second-order logic, first- and second-order variables are distinguished syntactically and cannot be grammatically substituted. According to a prominent argument for the deployment of these languages, these substitution failures are necessary to block the derivation of paradoxes that result from attempts to generalize over predicate interpretations. I first examine previous approaches which interpret second-order sentences using expressions of natural language and argue that these approaches undermine these syntactic restrictions. I then examine Williamson’s primitivist approach according to which (...) second-order sentences are not offered readings in a previously understood language. I argue that the syntactic restrictions alone do not block the derivation of the paradox, unless they are backed by a principled reason that the language cannot be expanded to allow the grammatical substitution of first- and second- order variables. I argue that there is neither a syntactic nor a semantic principle that prohibits such an expansion. (shrink)

One of the main reasons for the correspondence of regular languages and monadic second-order logic is that the class of regular languages is closed under images of surjective letter-to-letter homomorphisms. This closure property holds for structures such as finite words, finite trees, infinite words, infinite trees, elements of the free group, etc. Such structures can be modelled using monads. In this paper, we study which structures (understood via monads in the category of sets) are such that the class of regular (...) languages (i.e. languages recognized by finite algebras) are closed under direct images of surjective letter-to-letter homomorphisms. We provide diverse sufficient conditions for a monad to satisfy this property. We also present numerous examples of monads, including positive examples that do not satisfy our sufficient conditions, and counterexamples where the closure property fails. (shrink)

In this paper, we examine a fundamental problem that appears in Greek philosophy: the paradoxes of self-reference of the type of “Third Man” that appears first in Plato’s 'Parmenides', and is further discussed in Aristotle and the Peripatetic commentators and Proclus. We show that the various versions are analysed using different language, reflecting different understandings by Plato and the Platonists, such as Proclus, on the one hand, and the Peripatetics (Aristotle, Alexander, Eudemus), on the other hand. We show that the (...) Peripatetic commentators do not focus on Plato’s solution but primarily on the formulation of the “Third Man” paradox. On the contrary, Proclus seems to be convinced that Plato suggests a sound solution to the paradox by defining the predicate of similarity (homogeneity) that demarcates two types of homogeneous entities – the eide and the participants in them in a way that their confusion would be inadmissible. We claim that Plato’s solution follows a sound line of reasoning that is formalisable in a language of Frege-Russell type; hence there exists a model in which Plato’s reasoning is valid. Furthermore, we notice that Plato’s definition of the second-order predicate of similarity is attained by resorting to first-order entities. In this sense, Plato’s definition is comparable to Eudoxus’ definition of ratio, which is also attained by resorting to first-order objects. Consequently, Plato seems to follow a logical practice established by the mathematicians of the 5th century, notably Eudoxus, in his solution to the paradox. (shrink)

Husserl and Spatiality is an exploration of the phenomenology of space and embodiment, based on the work of Edmund Husserl. Little known in architecture, Husserl's phenomenology of embodied spatiality established the foundations for the works of later phenomenologists, including Maurice Merleau-Ponty's well-known phenomenology of perception. Through a detailed study of his posthumously published and unpublished manuscripts, DuFour examines the depth and scope of Husserl's phenomenology of space. The book investigates his analyses of corporeity and the 'lived body,' extending to questions (...) of intersubjective, intergenerational, and historical spatial experience, what DuFour terms the 'environmentality' of space. Combining in-depth architectural philosophical investigations of spatiality with a rich and intimate ethnography, Husserl and Spatiality speaks to themes in social and cultural anthropology from a theoretical perspective that addresses spatial practice and experience. Drawing on extensive fieldwork in Brazil, DuFour develops his analyses of Husserl's phenomenology through spatial accounts of ritual in the Afro-Brazilian religion of Candomblé. The result is a methodological innovation and unique mode of spatial description that DuFour terms a 'phenomenological ethnography of space.' The book's profoundly interdisciplinary approach makes an incisive contribution relevant to academics and students of architecture and architectural theory, anthropology and material culture, and philosophy and environmental aesthetics. (shrink)

There is an extensive literature related to the algebraization of first‐order logic. But the algebraization of full second‐order logic, or Henkin‐type second‐order logic, has hardly been researched. The question arises: what kind of set algebra is the algebraic version of a Henkin‐type model of second‐order logic? The question is investigated within the framework of the theory of cylindric algebras. The answer is: a kind of cylindric‐relativized diagonal restricted set algebra. And the class of the subdirect products of these set algebras (...) is the algebraization of Henkin‐type second‐order logic. It is proved that the algebraization of a complete calculus of the Henkin‐type second‐order logic is a class of a kind of diagonal restricted cylindric algebras. Furthermore, the connection with the non‐standard enlargements of standard complete second‐order structures is investigated. (shrink)

Neo-Fregean logicists claim that Hume's Principle (HP) may be taken as an implicit definition of cardinal number, true simply by fiat. A longstanding problem for neo-Fregean logicism is that HP is not deductively conservative over pure axiomatic second-order logic. This seems to preclude HP from being true by fiat. In this paper, we study Richard Kimberly Heck's Two-sorted Frege Arithmetic (2FA), a variation on HP which has been thought to be deductively conservative over second-order logic. We show that it isn't. (...) In fact, 2FA is not conservative over $n$-th order logic, for all $n \geq 2$. It follows that in the usual one-sorted setting, HP is not deductively Field-conservative over second- or higher-order logic. (shrink)

Preview:/Review: James G. Hart, Hedwig Conrad-Martius’ Ontological Phenomenology, ed. Rodney K.B Parker, 284 pages./ James Hart is an important phenomenological scholar and thinker who is the author of several books and many articles on Husserl, Husserl’s Utopian Poetics, and the phenomenological movement. This book is Hart’s dissertation written at the University of Chicago between 1969 and 1972. The book has an appendix of the opening sections of Conrad-Martius’s Metaphysics of the Earthly translated by Rodney Parker, who encouraged Hart to publish (...) this dissertation almost 50 years after he had defended it at the University of Chicago. Hart first encountered Conrad-Martius through his mentor at Catholic University, Thomas Prufer, who was a friend of Hedwig Conrad-Martius. The Prufers spent summers in Munich where Conrad-Martius taught and Prufer attended her lectures as a student. Hart’s major professor at Chicago was Mircea Eliade and his interest in myth coincided with Conrad-Martius’s work. But Hart’s dissertation was directed by Langdon Gilkey. Hart went to study in Munich in 1967, unfortunately, Conrad-Martius had died in 1966. Hedwig Conrad-Martius’ Ontological Phenomenology is the only monograph in English on the Munich phenomenologist Hedwig Conrad-Martius. She is usually considered a “marginal thinker” in the phenomenological movement and one of the Munich circle of phenomenology. The book is part of Springer’s series on “Women in the History of Philosophy and Sciences.” The discussion of women in the history of philosophy could give a broader picture of whether Conrad-Martius is a marginal figure or whether her thought should have a broader audience. Historical accident certainly has something to do with her relative obscurity. Being a woman, she had a difficult time getting to her habilitation. This situation only became worse in the Third Reich. (shrink)

En el presente artículo proponemos un abordaje de los análisis en torno al tacto y la mano en trabajos fundamentales de Husserl y Heidegger, en un diálogo con el análisis respectivos de J. Derrida. Por la vía de una lectura que reconoce continuidades y despliegues, buscaremos demostrar que las elaboraciones prácticas del tocar desarrolladas por Derrida articulan una comprensión en cierta continuidad con aquellas elaboraciones tradicionales, en el marco de una lectura singular de los textos respectivos.

In this essay, I study the departure performed in The Imaginary from the Husserlian position spanning from the Logical Investigations and the 1904/1905 lectures on the imagination. In Sartre’s conception, the imagination in its two forms is never intuitive. Moreover, in an act of imagination we can never find immanent sensible contents. In Husserl, the imagination in its two forms, is a sensible intuition, like perception. Furthermore, every act of imagination apprehends immanent sensible contents.

Semantic theories based on a hierarchy of types have prominently been used to defend the possibility of unrestricted quantification. However, they also pose a prima facie problem for it: each quantifier ranges over at most one level of the hierarchy and is therefore not unrestricted. It is difficult to evaluate this problem without a principled account of what it is for a quantifier to be unrestricted. Drawing on an insight of Russell’s about the relationship between quantification and the structure of (...) predication, we offer such an account. We use this account to examine the problem in three different type-theoretic settings, which are increasingly permissive with respect to predication. We conclude that unrestricted quantification is available in all but the most permissive kind of type theory. (shrink)

Orthodoxy holds that there is a determinate fact of the matter about every arithmetical claim. Little argument has been supplied in favour of orthodoxy, and work of Field, Warren and Waxman, and others suggests that the presumption in its favour is unjustified. This paper supports orthodoxy by establishing the determinacy of arithmetic in a well-motivated modal plural logic. Recasting this result in higher-order logic reveals that even the nominalist who thinks that there are only finitely many things should think that (...) there is some sense in which arithmetic is true and determinate. (shrink)

According to some philosophers, the Liar paradox arises because of a mistaken theory of truth. Its lesson is that we must reject some instances of the naive propositional truth-schema \It is true that \ if and only if \\. In this paper, I construct a novel semantic paradox in which no principle even analogous to the truth-schema plays any role. I argue that this undermines the claim that we ought to respond to the Liar by revising our theory of truth.

On a widespread naturalist view, the meanings of mathematical terms are determined, and can only be determined, by the way we use mathematical language—in particular, by the basic mathematical principles we’re disposed to accept. But it’s mysterious how this can be so, since, as is well known, minimally strong first-order theories are non-categorical and so are compatible with countless non-isomorphic interpretations. As for second-order theories: though they typically enjoy categoricity results—for instance, Dedekind’s categoricity theorem for second-order PA and Zermelo’s quasi-categoricity (...) theorem for second-order ZFC—these results require full second-order logic. So appealing to these results seems only to push the problem back, since the principles of second-order logic are themselves non-categorical: those principles are compatible with restricted interpretations of the second-order quantifiers on which Dedekind’s and Zermelo’s results are no longer available. In this paper, we provide a naturalist-friendly, non-revisionary solution to an analogous but seemingly more basic problem—Carnap’s Categoricity Problem for propositional and first-order logic—and show that our solution generalizes, giving us full second-order logic and thereby securing the categoricity or quasi-categoricity of second-order mathematical theories. Briefly, the first-order quantifiers have their intended interpretation, we claim, because we’re disposed to follow the quantifier rules in an open-ended way. As we show, given this open-endedness, the interpretation of the quantifiers must be permutation-invariant and so, by a theorem recently proved by Bonnay and Westerståhl, must be the standard interpretation. Analogously for the second-order case: we prove, by generalizing Bonnay and Westerståhl’s theorem, that the permutation invariance of the interpretation of the second-order quantifiers, guaranteed once again by the open-endedness of our inferential dispositions, suffices to yield full second-order logic. (shrink)

This article explores Jan Patočka’s notion of “asubjective phenomenology,” which the Czech philosopher elaborated in the mature phase of his thought. More specifically, it proposes to analyze that notion in light of Patočka’s interpretation of Edmund Husserl’s Logical Investigations, in which he identifies the original, though implicit, possibility of a phenomenology independent of a subjective foundation. In the first part of the paper, the author offers an interpretation of Husserls’ concept of “theory in general” as the original model of the (...) Patočkan phenomenal field, which, just like the logical dimension thematized by Husserl in the Prolegomena to Pure Logic, is independent of both objective structures and subjective conditions. It is reasonable to assume that the absence, in Logical Investigations, of “transcendental consciousness,” inspired Patočka in conceiving the manifestation of the object as a thing’s “showing-itself.” This idea is advanced in the second part of the article. Lastly, the final section of the article discusses the concept of “representative” (the sensory content of the intentional act representation) as the second and most significant seed of “asubjective phenomenology” that can be retraced in Husserl’s Logical Investigations. (shrink)

Kurt Gödel’s version of the Ontological Proof derives rather than assumes the crucial Possibility Claim: the claim that it is possible that something God-like exists. Gödel’s derivation starts off with a proof of the Possible Instantiation of the Positive: the principle that, if a property is positive, it is possible that there exists something that has that property. I argue that Gödel’s proof of this principle relies on some implausible axiological assumptions but it can be patched so that it only (...) relies on plausible principles. But Gödel’s derivation of the Possibility Claim also needs a substantial axiological assumption, which is still open to doubt. (shrink)

According to one prominent strand of mainstream logic and metaphysics, identity is indistinguishability. Priest has recently argued that this permits counterexamples to the transitivity and substitutivity of identity within dialetheic metaphysics, even in paradigmatically extensional contexts. This paper investigates two alternative regimentations of indistinguishability. Although classically equivalent to the standard regimentation on which Priest focuses, these alternatives are strictly stronger than it in dialetheic settings. Both regimentations are transitive, and one satisfies substitutivity. It is argued that both regimentations provide better (...) candidates to occupy the core theoretical role of numerical identity than does the standard regimentation. (shrink)

The rather unrestrained use of second-order logic in the neo-logicist program is critically examined. It is argued in some detail that it brings with it genuine set-theoretical existence assumptions and that the mathematical power that Hume’s Principle seems to provide, in the derivation of Frege’s Theorem, comes largely from the ‘logic’ assumed rather than from Hume’s Principle. It is shown that Hume’s Principle is in reality not stronger than the very weak Robinson Arithmetic Q. Consequently, only a few rudimentary facts (...) of arithmetic are logically derivable from Hume’s Principle. And that hardly counts as a vindication of logicism. (shrink)

A prominent objection against the logicality of second-order logic is the so-called Overgeneration Argument. However, it is far from clear how this argument is to be understood. In the first part of the article, we examine the argument and locate its main source, namely, the alleged entanglement of second-order logic and mathematics. We then identify various reasons why the entanglement may be thought to be problematic. In the second part of the article, we take a metatheoretic perspective on the matter. (...) We prove a number of results establishing that the entanglement is sensitive to the kind of semantics used for second-order logic. These results provide evidence that by moving from the standard set-theoretic semantics for second-order logic to a semantics which makes use of higher-order resources, the entanglement either disappears or may no longer be in conflict with the logicality of second-order logic. (shrink)

In two of the earliest papers on extending modal logic with propositional quantifiers, R. A. Bull and K. Fine studied a modal logic S5Π extending S5 with axioms and rules for propositional quantification. Surprisingly, there seems to have been no proof in the literature of the completeness of S5Π with respect to its most natural algebraic semantics, with propositional quantifiers interpreted by meets and joins over all elements in a complete Boolean algebra. In this note, we give such a proof. (...) This result raises the question: For which normal modal logics. (shrink)

The chapter provides an overview on what it means to be in a world that is uncertain, e.g., how under conditions of limited understanding any activity is an activity that designs and constructs, and how designing objects, spaces, and situations relates to the (designed) meta-world of second-order cybernetics. Designers require a framework that is open, but one that supplies ethical guidance when ‘constructing’ something new. Relating second-order design thinking to insights in philosophy and aesthetics, the chapter argues that second-order cybernetics (...) provides a response to this ethical challenge and essentially it entails a poetics of designing. //// 'A Poetics of Designing' is part of the first book-length collection of texts in Design Cybernetics. It introduces the subject from the point of view of aesthetics. Importantly, the chapter argues that second-order cybernetics circumvents the necessity for a muse inspired artist or genius as a mediator between higher spirits and life, in favour of artists and designers who have true agency. //// Cybernetics is often associated with AI, which is, however, only one of the branches that developed on the basis of the interdisciplinary research begun in the 1940s and entitled cybernetics. I hope the chapter contributes to a better understanding of the second-order cybernetics that has been conceived in close relationship with art and design from the late 60s onwards. (shrink)

This paper presents two different, although related, approaches to the problem of the experience of the other person: E. Husserl’s phenomenology of intersubjectivity and E. Levinas’ ethics. I begin by addressing the transcendental significance of the experience of intersubjectivity in the broader context of Husserl’s transcendental phenomenology. I then turn to Husserl’s solution to the paradox of constituting the alter ego, identifying and elucidating the key‑concepts of his inquiry. I hold that throughout his analysis there is a dominant underlying meaning (...) in which the alterity of the other person is progressively suppressed and, ultimately, elided. Finally, I discuss the consequences of Husserl’s analysis of the other in light of Levinas’ ethics. I hold that Husserl’s claim that there is a fundamental difference between the experience of myself and my analogical experience of the other is the basis upon which Levinas’ develops a new concept of experience, not as perception but as encounter. Upon close reading, I claim that Levinas’ revision of the topic of alterity is, ultimately, a consequence of Husserl’s transcendental analysis of intersubjectivity. (shrink)

In two recent papers, Bob Hale has attempted to free second-order logic of the 'staggering existential assumptions' with which Quine famously attempted to saddle it. I argue, first, that the ontological issue is at best secondary: the crucial issue about second-order logic, at least for a neo-logicist, is epistemological. I then argue that neither Crispin Wright's attempt to characterize a `neutralist' conception of quantification that is wholly independent of existential commitment, nor Hale's attempt to characterize the second-order domain in terms (...) of definability, can serve a neo-logicist's purposes. The problem, in both cases, is similar: neither Wright nor Hale is sufficiently sensitive to the demands that impredicativity imposes. Finally, I defend my own earlier attempt to finesse this issue, in "A Logic for Frege's Theorem", from Hale's criticisms. (shrink)

The article introduces the problematics of the classical two-valued logic on which Western thought is generally based, outlining that under the conditions of its logical assumptions the subject I is situated in a world that it cannot address. In this context, the article outlines a short history of cybernetics and the shift from first- to second-order cybernetics. The basic principles of Gordon Pask’s 1976 Conversation Theory are introduced. It is argued that this second-order theory grants agency to others through a (...) re-conception of living beings as You logically transcending the I. The key principles of Conversation Theory are set in relation to the poetic forms of discourse that played a key role in art as well as philosophical thinking in China in the past. Second-order thinking, the article argues, is essentially poetic. It foregoes prediction in favour of the potentiality of encountering tomorrow’s delights. (shrink)

The paradox that appears under Burali-Forti’s name in many textbooks of set theory is a clever piece of reasoning leading to an unproblematic theorem. The theorem asserts that the ordinals do not form a set. For such a set would be—absurdly—an ordinal greater than any ordinal in the set of all ordinals. In this article, we argue that the paradox of Burali-Forti is first and foremost a problem about concept formation by abstraction, not about sets. We contend, furthermore, that some (...) hundred years after its discovery the paradox is still without any fully satisfactory resolution. A survey of the current literature reveals one key assumption of the paradox that has gone unquestioned, namely the assumption that ordinals are objects. Taking the lead from Russell’s no class theory, we interpret talk of ordinals as an efficient way of conveying higher-order logical truths. The resulting theory of ordinals is formally adequate to standard intuitions about ordinals, expresses a conception of ordinal number capable of resolving Burali-Forti’s paradox, and offers a novel contribution to the longstanding program of reducing mathematics to higher-order logic. (shrink)

This dissertation develops an inferentialist theory of meaning. It takes as a starting point that the sense of a sentence is determined by the rules governing its use. In particular, there are two features of the use of a sentence that jointly determine its sense, the conditions under which it is coherent to assert that sentence and the conditions under which it is coherent to deny that sentence. From this starting point the dissertation develops a theory of quantification as marking (...) coherent ways a language can be expanded and modality as the means by which we can reflect on the norms governing the assertion and denial conditions of our language. If the view of quantification that is argued for is correct, then there is no tension between second-order quantification and nominalism. In particular, the ontological commitments one can incur through the use of a quantifier depend wholly on the ontological commitments one can incur through the use of atomic sentences. The dissertation concludes by applying the developed theory of meaning to the metaphysical issue of necessitism and contingentism. Two objections to a logic of contingentism are raised and addressed. The resulting logic is shown to meet all the requirement that the dissertation lays out for a theory of meaning for quantifiers and modal operators. (shrink)

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.

Consider one of several things. Is the one thing necessarily one of the several? This key question in the modal logic of plurals is clarified. Some defenses of an affirmative answer are developed and compared. Various remarks are made about the broader philosophical significance of the question.

If I say that Alice is everything Oscar hopes to be, I seem to be quantifying over properties. That suggestion faces an immediate difficulty, however: though Alice may be wise, she surely is not the property of being wise. This problem can be framed in terms of a substitution failure: if a predicate like ‘happy’ denoted a property, we would expect pairs like ‘Oscar is happy’ and ‘Oscar is the property of being happy’ to be equivalent, which they clearly are (...) not. I argue that a Fregean response that draws a distinction between objects and concepts faces serious difficulties, and that a syntactic solution to the substitution problem likewise fails. I propose to account for the substitution failure by instead distinguishing different ways that expressions can stand for properties: whereas ‘the property of being happy’ refers to a property, ‘happy’ expresses or ascribes that property. I go on to compare this view to proposals made by Wright and Liebesman, and end by drawing out a consequence my proposal has for a debate about the ontological commitments of predicatively quantified sentences. (shrink)

Review of Syraya Chin-Mu Yang, Duen-Min Deng, Hanti Lin, Structural Analysis of Non-Classical Logics: The Proceedings of the Second Taiwan Philosophical Logic Colloquium, 278 pp.

Bob Hale’s distinguished record of research places him among the most important and influential contemporary analytic metaphysicians. In his deep, wide ranging, yet highly readable book Necessary Beings, Hale draws upon, but substantially integrates and extends, a good deal his past research to produce a sustained and richly textured essay on — as promised in the subtitle — ontology, modality, and the relations between them. I’ve set myself two tasks in this review: first, to provide a reasonably thorough (if not (...) exactly comprehensive) overview of the structure and content of Hale’s book and, second, to a limited extent, to engage Hale’s book philosophically. I approach these tasks more or less sequentially: Parts I and 2 of the review are primarily expository; in Part 3 I adopt a somewhat more critical stance and raise several issues concerning one of the central elements of Hale’s account, his essentialist theory of modality. (shrink)

Boolos has suggested a plural interpretation of second-order logic for two purposes: to escape Quine’s allegation that second-order logic is set theory in disguise, and to avoid the paradoxes arising if the second-order variables are given a set-theoretic interpretation in second-order set theory. Since the plural interpretation accounts only for monadic second-order logic, Rayo and Yablo suggest an new interpretation for polyadic second-order logic in a Boolosian spirit. The present paper argues that Rayo and Yablo’s interpretation does not achieve the (...) goal. (shrink)

Second-order logic and modal logic are both, separately, major topics of philosophical discussion. Although both have been criticized by Quine and others, increasingly many philosophers find their strictures uncompelling, and regard both branches of logic as valuable resources for the articulation and investigation of significant issues in logical metaphysics and elsewhere. One might therefore expect some combination of the two sorts of logic to constitute a natural and more comprehensive background logic for metaphysics. So it is somewhat surprising to find (...) that philosophical discussion of secondorder modal logic is almost totally absent, despite the pioneering contribution of Barcan. (shrink)

If Art is smart and Art is rich, then someone is both smart and rich – namely, Art. And if Art is smart and Bart is smart, then Art is something that Bart is, too – namely, smart. The first claim involves first-order quantification, a generalization concerning what kinds of things there are. The second involves second-order quantification, a generalization concerning what there is for things to be. Or so it appears. Following W.V.O. Quine, many philosophers have endorsed a thesis (...) of Ontological Collapse about second-order quantification. They maintain that ultimately, second-order quantification reduces to first-order quantification over sets or properties, and therefore also carries the latter’s distinctive ontological commitments. In this revised version of his doctoral dissertation, awarded the Wolfgang-Stegmüller-Prize in 2012, Stephan Krämer examines the major arguments for Ontological Collapse in detail and finds all of them wanting. Quantifications, he argues, fall into at least two irreducible kinds: those on what things there are, and those on what there is for things to be. (shrink)

This paper examines the ontological commitments of the second-order language of arithmetic and argues that they do not extend beyond the first-order language. Then, building on an argument by George Boolos, we develop a Tarski-style definition of a truth predicate for the second-order language of arithmetic that does not involve the assignment of sets to second-order variables but rather uses the same class of assignments standardly used in a definition for the first-order language.

There has been very little discussion of the appropriate principles to govern a modal logic of plurals. What debate there has been has accepted a principle I call (Necinc); informally if this is one of those then, necessarily: this is one of those. On this basis Williamson has criticised the Boolosian plural interpretation of monadic second-order logic. I argue against (Necinc), noting that it isn't a theorem of any logic resulting from adding modal axioms to the plural logic PFO+, and (...) showing that the most obvious formal argument in its favour is question begging. I go on to discuss the behaviour of natural language plurals, motivating a case against (Necinc) by developing a case that natural language plural terms are not de jure rigid designators. The paper concludes by developing a model theory for modal PFO-f which does not validate (Necinc). An Appendix discusses (Necinc) in relation to counterpart theory. Of course, it would be a mistake to think that the rules for "multiple pointing" follow automatically from the rules for pointing proper. Max Black—The Elusiveness of Sets In some influential articles during the 1980s George Boolos proposed an interpretation of monadic second-order logic in terms of plural quantification [4, 5]. One objection to this proposal, pressed by Williamson [22, 456-7], focuses on the modal behaviour of plural variables, arguing that the proposed interpretation yields the wrong results in respect of the modal status of atomic predications. In the present paper I will present this objection and argue against it. In the course of developing the argument, I will have cause to consider the under-investigated question of how a logic for plurals should be extended to incorporate modal operators. (shrink)

We try to answer the question which is the “right” foundation of mathematics, second order logic or set theory. Since the former is usually thought of as a formal language and the latter as a first order theory, we have to rephrase the question. We formulate what we call the second order view and a competing set theory view, and then discuss the merits of both views. On the surface these two views seem to be in manifest conflict with each (...) other. However, our conclusion is that it is very difficult to see any real difference between the two. We analyze a phenomenon we call internal categoricity which extends the familiar categoricity results of second order logic to Henkin models and show that set theory enjoys the same kind of internal categoricity. Thus the existence of non-standard models, which is usually taken as a property of first order set theory, and categoricity, which is usually taken as a property of second order axiomatizations, can coherently coexist when put into their proper context. We also take a fresh look at complete second order axiomatizations and give a hierarchy result for second order characterizable structures. Finally we consider the problem of existence in mathematics from both points of view and find that second order logic depends on what we call large domain assumptions, which come quite close to the meaning of the axioms of set theory. (shrink)