Recent years have seen a certain impatience with John Rawls's approach to political philosophy and calls for the discipline to move beyond it. One source of dissatisfaction is Rawls's idea of a well-ordered society. In a recent article, Alex Schaefer has tried to give further impetus to this movement away from Rawlsian theorizing by pursuing a question about well-ordered societies that he thinks other critics have not thought to ask. He poses that question in the title of his article: (...) “Is Justice a Fixed Point?.” Though Schaefer is critical of Rawlsian political theorizing, I shall contend that his arguments also suggest two paths forward for those who would follow the Rawlsian approach. First, the intellectual devices Schaefer deploys help those who would continue the Rawlsian project to see, and precisely to chart, the next step that that project needs to take—a step necessitated by a concession Rawls himself made late in the development of political liberalism. Second, the clarity and economy with which Schaefer lays out his alternative to the Rawlsian approach make it possible to state some fundamental Rawlsian challenges to a form of theorizing that has considerable appeal to many critics of that approach. (shrink)

This paper introduces a new kind of fixed-point semantics, filling a gap within approaches to Liar-like paradoxes involving fixed-point models à la Kripke (1975). The four-valued models presented below, (i) unlike the three-valued, consistent fixed-point models defined in Kripke (1975), are able to differentiate between paradoxical and pathological-but-unparadoxical sentences, and (ii) unlike the four-valued, paraconsistent fixed-point models first studied in Visser (1984) and Woodruff (1984), preserve consistency and groundedness of truth.

Following F. William Lawvere, we show that many self-referential paradoxes, incompleteness theorems and fixed point theorems fall out of the same simple scheme. We demonstrate these similarities by showing how this simple scheme encompasses the semantic paradoxes, and how they arise as diagonal arguments and fixed point theorems in logic, computability theory, complexity theory and formal language theory.

The article is about one of the vital problem for analytic philosophy which is how to define truth value for sentences which include their own truth predicate. The aim of the article is to determine Saul Kripke’s approach to widen epistemological truth to create a systemic model of truth. Despite a lot of work on the subject, the theme of truth is no less relevant to modern philosophy. With the help of S. Kripke’s article “Outline of the Theory of (...) Truth” and R. L. Kirkham’s work “Theories of Truth: A Critical Introduction” the author tried to represent a non-classical approach which is now known as Saul Kripke’s truth value gaps theory. Considering his solving of the Liar Paradox, as well as the Strenghened Liar, it is obvious that there could be the circumstances (or facts) that make sentences have no truth value. In that case the solving of the paradox attracts Kleene’s non-classical three-valued logic which contains the third way and the solution falls into the gap between truth and falsity. Hence there are no relevant and full satisfactory ways to solve the Liar’s Paradox by the language-levels ap- proach. The task consists in an extension of the approach to natural languages and elimination of an ad hoc element as well. Besides that, the language-levels approach refers to the speaker that means that only the last one is allowed to define the hierarchy of the levels and truth value of sentence, but often he does not know what level he is speaking of. As Kripke stated, contingent facts can lead to a paradox which isn’t allowed for a logical point of view. However usage of mathematical apparatus allows the theory in question to be universalized and moreover paves the way to futher epistemological develop- ment of the problem in question. As Kripke’s theory is formalized and presented as a functional series, it gives access to a system model of truth whose elements would be epistemological theories (concepts) of truth. Such a model, for instance, confirms the validity of the deflationary concept of truth. Refs 7. (shrink)

This manuscript investigates fixed point of single-valued Hardy-Roger’s type F -contraction globally as well as locally in a convex b -metric space. The paper, using generalized Mann’s iteration, iterates fixed point of the abovementioned contraction; however, the third axiom of the F -contraction is removed, and thus the mapping F is relaxed. An important approach used in the article is, though a subset closed ball of a complete convex b -metric space is not necessarily complete, the convergence of the (...) Cauchy sequence is confirmed in the subset closed ball. The results further lead us to some important corollaries, and examples are produced in support of our main theorems. The paper most importantly presents application of our results in finding solution to the integral equations. (shrink)

Termination for classical natural deduction is difficult in the presence of commuting/permutative conversions for disjunction. An approach based on reducibility candidates is presented that uses non-strictly positive inductive definitions.It covers second-order universal quantification and also the extension of the logic with fixed points of non-strictly positive operators, which appears to be a new result.Finally, the relation to Parigot’s strictly positive inductive definition of his set of reducibility candidates and to his notion of generalized reducibility candidates is explained.

Kremer presented three approaches of comparing fixed-point and revision theories of truth in Kremer, 363–403, 2009). Using these approaches, he established the relationships among ten fixed-point theories suggested by Kripke in, 690–716, 1975) and three revision theories presented by Gupta and Belnap in. This paper continues Kremer’s work. We add five other revision theories to the comparisons, including the theory proposed by Gupta in, 1–60, 1982), the theory proposed by Herzberger in, 61–102, 1982), the theory based on fully-varied revision sequences (...) proposed by Gupta and Belnap in, the theory proposed by Yaqūb in, and the theory based on weakly consistent revision sequences. We show that, the notion of Thomason model defined by Belnap’s limit rule is not equivalent to the one defined by Gupta’s limit rule, and that the theory based on fully-varied revision sequences is ≤2-equivalent to the one based on the greatest intrinsic fixed point of σ. (shrink)

The purpose of this article is to present a new theory for fixed points over arithmetic which allows the building up of fixed points in a very nested and entangled way. But in spite of its great expressive power we can show that the proof-theoretic strength of our theory—which is intensional in a meaning to be described below—is characterized by the Feferman–Schütte ordinal Γ0. Our approach is similar to the building up of fixed points over state spaces in the (...) propositional modal μ-calculus. (shrink)

The new concept of lambda calculi with monotone inductive types is introduced byhelp of motivations drawn from Tarski's fixed-point theorem (in preorder theory) andinitial algebras and initial recursive algebras from category theory. They are intendedto serve as formalisms for studying iteration and primitive recursion ongeneral inductively given structures. Special accent is put on the behaviour ofthe rewrite rules motivated by the categorical approach, most notably on thequestion of strong normalization (i.e., the impossibility of an infinitesequence of successive rewrite steps). (...) It is shown that this key propertyhinges on the concrete formulation. The canonical system of monotone inductivetypes, where monotonicity is expressed by a monotonicity witness beinga term expressing monotonicity through its type, enjoys strong normalizationshown by an embedding into the traditional system of non-interleavingpositive inductive types which, however, has to be enriched by the parametricpolymorphism of system F. Restrictions to iteration on monotone inductive typesalready embed into system F alone, hence clearly displaying the differencebetween iteration and primitive recursion with respect to algorithms despitethe fact that, classically, recursion is only a concept derived from iteration. (shrink)

The Embracing Revenge account of semantic paradox avoids the expressive limitations of previous approaches based on the Kripkean fixed point construction by replacing a single language with an indefinitely extensible sequence of languages, each of which contains the resources to fully characterize the semantics of the previous languages. In this paper we extend the account developed in Cook, Cook, Schlenker, and Tourville and Cook via the addition of intensional operators such as ``is paradoxical''. In this extended framework we are able (...) to characterize the difference between sentences, such as the Liar and the Truth-teller, that receive the same semantic value in minimal fixed points yet seem to involve distinct semantic phenomena. (shrink)

Buchholz’s Ω μ+1-rules provide a major tool for the proof-theoretic analysis of arithmetical inductive definitions. The aim of this paper is to put this approach into the new context of modal fixed point logic. We introduce a deductive system based on an Ω-rule tailored for modal fixed point logic and develop the basic techniques for establishing soundness and completeness of the corresponding system. In the concluding section we prove a cut elimination and collapsing result similar to that of Buchholz (...) (Iterated inductive definitions and subsystems of analysis: recent proof theoretic studies. Lecture notes in mathematics, vol. 897, pp. 189–233, Springer, Berlin, 1981). (shrink)

Understanding recreational experiences is a longstanding research tradition and key to effective management. Given the complexities of human experience, many approaches have been applied to study recreational experience. Two such approaches are the experiential approach (based in a positivistic paradigm) and emergent experience (based in an interpretive paradigm). While viewed as being complementary, researchers have not offered guidance for incorporating the approaches into a common model of recreational experience. This study utilized longitudinal, qualitative data to examine aspects of recreational (...) experience posited by these two approaches. Results provided a framework for synthesizing across the two approaches. Respondents had clear pre-activity expectations, and most respondents realized their expected outcomes. This supports the experiential approach. Of the 48 activity narratives, 27 experienced something unexpected, and 45 described process-oriented, intrinsic motivation, suggesting evidence of emergent and unique characteristics specific to an individual’s realization of recreational experience. This supports the application of the emergent experience approach to understand how individuals create meaning from recreational engagements. The paper proposes a model for integrating results of the two approaches. While not advocating for any specific approach, the findings can serve as an example of building a holistic model of the outdoor recreation experience. The purpose of the model is to allow for a more complete understanding of how individuals create recreation experiences, more complete documentation of the benefits of outdoor recreation for both researchers and managers, and better synthesis across studies. (shrink)

Given a simple non-trivial finite-dimensional Lie algebra L, fields $K_i$ and Chevalley groups $L(K_i)$ , we first prove that $\Pi_{\mathcal{U}} L(K_i)$ is isomorphic to $L(\Pi_{\mathcal{U}}K_i)$ . Then we consider the case of Chevalley groups of twisted type ${}^n\!L$ . We obtain a result analogous to the previous one. Given perfect fields $K_i$ having the property that any element is either a square or the opposite of a square and Chevalley groups ${}^n\!L(K_i)$ , then $\pu{}^n\!L(K_i)$ is isomorphic to ${}^n\!L(\pu K_i)$ . (...) We apply our results to prove the decidability of the set of sentences true in almost all finite groups of the form L(K) where K is a finite field and L a fixed untwisted Chevalley type. (shrink)

We consider the reduct to the module language of certain theories of fields with a non surjective endomorphism. We show in some cases the existence of a model companion. We apply our results for axiomatizing the reduct to the theory of modules of non principal ultraproducts of separably closed fields of fixed but non zero imperfection degree.

"Philosophy for Children: a Way to Reconcile Disciplinary Teaching and School Life? Drawing mainly on John Dewey's writings, this contribution aims to extend the dualism of a traditional conception of education at the epistemological, pedagogical and organizational levels. This conception was already criticised by this author at the beginning of the 20th century and still remains widely present today among the school community. Through this approach, we demonstrate that the dualist approach is as many obstacles to be removed (...) in the process both to improve and rebuild a better education. The hypothesis defended here consists to demonstrate how philosophy for children, strengthened by its pragmatist heritage, can challenge these dualisms and thereby jeopardize the traditional conception of education. Keywords: John Dewey, philosophy of education, co-curriculum, school life, philosophy for children ". (shrink)

We consider separably closed fields of characteristic $p > 0$ and fixed imperfection degree as modules over a skew polynomial ring. We axiomatize the corresponding theory and we show that it is complete and that it admits quantifier elimination in the usual module language augmented with additive functions which are the analog of the $p$-component functions.

Some years ago, Yablo gave a paradox concerning an infinite sequence of sentences: if each sentence of the sequence is 'every subsequent sentence in the sequence is false', a contradiction easily follows. In this paper we suggest a formalization of Yablo's paradox in algebraic and topological terms. Our main theorem states that, under a suitable condition, any continuous function from 2N to 2N has a fixed point. This can be translated in the original framework as follows. Consider an infinite sequence (...) of sentences, where any sentence refers to the truth values of the subsequent sentences: if the corresponding function is continuous, no paradox arises. (shrink)

In this article we consider the material dimensions of schooling as constitutive of the possibilities inherent in “fixing” education. We begin by mapping out the problem of “fixing education,” pointing to the necrophilic tendencies of contemporary education—a desire to kill what otherwise might be life-giving. In this sense, to “fix” education is to make otherwise fluid processes-of-living static. We next point to the material realities of this move to fix. After establishing the material consequences of perpetually fixing schools, we provide (...) a brief overview of two critical perspectives that might be shown as attempts to “unfix” education: critical pedagogy and unschooling. Though both offer critiques of normative education, these approaches are also bound by their failure to fully engage with the material dimensions of schooling. As such, both critical pedagogy and unschooling inadvertently cut off key possibilities for human flourishing within educational environments. In their rush to “unfix”—to counter the necrophilic tendencies of contemporary education—these approaches exclude or otherwise foreclose upon resistive challenges to the normative order that extend from the margins. In response, we turn to the possibilities for unschooling within the materially public spaces of schools. These are the spaces where fixity fails—possibility extends from unschooling in schools, from unfixing the process of fixing education. We end by considering the possibilities inherent in Community Service Learning as a valuable means to engage in a radically public, and unfixed, educational system. (shrink)

In this article we consider the material dimensions of schooling as constitutive of the possibilities inherent in “fixing” education. We begin by mapping out the problem of “fixing education,” pointing to the necrophilic tendencies of contemporary education—a desire to kill what otherwise might be life-giving. In this sense, to “fix” education is to make otherwise fluid processes-of-living static. We next point to the material realities of this move to fix. After establishing the material consequences of perpetually fixing schools, we provide (...) a brief overview of two critical perspectives that might be shown as attempts to “unfix” education: critical pedagogy and unschooling. Though both offer critiques of normative education, these approaches are also bound by their failure to fully engage with the material dimensions of schooling. As such, both critical pedagogy and unschooling inadvertently cut off key possibilities for human flourishing within educational environments. In their rush to “unfix”—to counter the necrophilic tendencies of contemporary education—these approaches exclude or otherwise foreclose upon resistive challenges to the normative order that extend from the margins. In response, we turn to the possibilities for unschooling within the materially public spaces of schools. These are the spaces where fixity fails—possibility extends from unschooling in schools, from unfixing the process of fixing education. We end by considering the possibilities inherent in Community Service Learning as a valuable means to engage in a radically public, and unfixed, educational system. (shrink)

I will argue that Roy Cook’s (forthcoming) reformulation of Yablo’s Paradox in the infinitary system D is a genuinely non-circular paradox, but for different reasons than the ones he sustained. In fact, the first part of the job will be to show that his argument regarding the absence of fixed points in the construction is insufficient to prove the noncircularity of it; at much it proves its non-self referentiality. The second is to reconsider the structural collapse approach Cook rejects, (...) and argue that a correct understanding of it leads us to the claim that the infinitary paradox is actually non-circular. En este trabajo argumentaré que la reformulación que Roy Cook (forthcoming) hace de la paradoja de yablo en el sistema infinitario D es una genuina paradoja no circular, pero por motivos distintos a los defendidos por ese autor. La primera parte del trabajo consiste en mostrar que la ausencia de puntos fijos en la construcción es insuficiente para demostrar su no circularidad, a lo sumo prueba su no autorreferencialidad. La segunda parte consiste en volver a considerar el enfoque del colapso estructural que Cook rechaza, y argumentar que una correcta comprensión del mismo revela que la paradoja es genuinamente no circular. (shrink)

In this article the authors1 approach material and symbolic violence through transdisciplinary readings of theoretical debates, fiction and empirical narratives. They make use of the concept of turning points which disrupt dichotomous and static categorizations of victim and survivor, and their association with passivity and agency respectively. In situations of violence, turning points represent temporality instead of timelessness, dialogism instead of monologism, multilayering rather than any fixed identity. The authors draw on the theorists Bakhtin and Certeau, whose work highlights (...) the significance of meaning-making between self and other. They analyse empirical and fictional narratives to understand the creation of dialogic spaces, a space that both subordinates and subverts. Pointing to the procedural nature of turning points within the everyday, the authors argue that women, despite the pain and trauma, are neither just a victim nor just a survivor in a violent relationship. (shrink)

Artificial Neural Networks have reached “grandmaster” and even “super-human” performance across a variety of games, from those involving perfect information, such as Go, to those involving imperfect information, such as “Starcraft”. Such technological developments from artificial intelligence (AI) labs have ushered concomitant applications across the world of business, where an “AI” brand-tag is quickly becoming ubiquitous. A corollary of such widespread commercial deployment is that when AI gets things wrong—an autonomous vehicle crashes, a chatbot exhibits “racist” behavior, automated credit-scoring processes (...) “discriminate” on gender, etc.—there are often significant financial, legal, and brand consequences, and the incident becomes major news. As Judea Pearl sees it, the underlying reason for such mistakes is that “... all the impressive achievements of deep learning amount to just curve fitting.” The key, as Pearl suggests, is to replace “reasoning by association” with “causal reasoning” —the ability to infer causes from observed phenomena. It is a point that was echoed by Gary Marcus and Ernest Davis in a recent piece for theNew York Times: “we need to stop building computer systems that merely get better and better at detecting statistical patterns in data sets—often using an approach known as ‘Deep Learning’—and start building computer systems that from the moment of their assembly innately grasp three basic concepts: time, space, and causality.” In this paper, foregrounding what in 1949 Gilbert Ryle termed “a category mistake”, I will offer an alternative explanation for AI errors; it is not so much that AI machinery cannot “grasp” causality, but that AI machinery (qua computation) cannot understand anything at all. (shrink)

In response to the liar’s paradox, Kripke developed the fixed-point semantics for languages expressing their own truth concepts. Kripke’s work suggests a number of related fixed-point theories of truth for such languages. Gupta and Belnap develop their revision theory of truth in contrast to the fixed-point theories. The current paper considers three natural ways to compare the various resulting theories of truth, and establishes the resulting relationships among these theories. The point is to get a sense of the lay of (...) the land amid a variety of options. Our results will also provide technical fodder for the methodological remarks of the companion paper to this one. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Approaching History through the Future: Some Thoughts from a Feminist PragmatistErin McKennai was recently asked to write on the philosophy of history from a pragmatist perspective. My initial response was that this is not my area of specialization and that I didn’t really have much to say. Then I realized that it was interesting to think about how I view and use notions of history in my work as (...) a feminist pragmatist. It turns out that in my own work, there is a theme of approaching/understanding history through the possibilities of the future. Rather than being confined by settled or fixed views of the present or the past, the present and past are better seen as possibilities for shaping new and different futures. This can be unsettling for many, as humans often like to justify practices and institutions with the idea that “it has to be this way” and/or “it has always been this way.” But unsettling this habit is important if we hope to approach conflict and disagreements in a productive manner that avoids dogmatism and division.Examining my own use of history in my varied philosophical work turned out to be interesting and instructive. It also revealed my reliance on theorists such as Jane Addams, Anna Julia Cooper, and John Dewey in my writing and my teaching. Usually, I work with implicit notions of history and its role in my philosophical writing. The one exception to that was in writing American Philosophy: From Wounded Knee to the Present, co-authored with Scott L. Pratt. In that work, we explicitly took up a pragmatist approach to history rooted in the work of John Dewey. There, we wrote:For Peirce, James, and Dewey, philosophy worth the name began in response to experienced problems—situations marked by confusion, doubt, indeterminacy—and then returned to these problems, aiming to transform and reconstruct them in ways that allowed the inquirer to go forward, to encounter still more experience. Philosophy, then should be understood as an activity that arises from experience. Since [End Page 71] experience is framed by language, culture and history, philosophy is not a transcendental practice engaged with the really real and truly true.(McKenna and Pratt 3)In “Philosophy and Civilization,” Dewey noted that philosophy is closely tied to the histories of cultures. These ties are mutually transformative, as the philosophy produced is rooted in, and shaped by, the place and time just as it then transforms the place, time, and traditions that give rise to it.Dewey’s own philosophy of history guided our work in American Philosophy: From Wounded Knee to the Present as we strove to offer a history of American philosophy that acknowledges its rootedness in particular times and places. In Logic: The Theory of Inquiry, Dewey noted that history is always in the making, when he wrote:The slightest reflection shows that the conceptual material employed in writing history is that of the period in which a history is written. There is no material available for leading principles and hypotheses save that of the historic present. As culture changes, the conceptions that are dominant in a culture change. Of necessity, new standpoints for viewing, appraising and ordering data arise. History is then rewritten. Material that had formerly been passed by, offers itself as data because the new conceptions propose new problems for solution requiring new factual material for statement and test.(LW 12:232–33)Dewey went on to argue that changes happening in the present put the past into a new perspective and bring to light new problems. This means that one’s understanding of the past is changed, and “we gain new instruments for estimating the force of present conditions as potentialities of the future” (LW 12:238). For this reason, in American Philosophy: From Wounded Knee to the Present, Pratt and I embedded the history of American philosophy in actual historical events that we thought could profitably provide context for the philosophy and could themselves be rethought from our present vantage point. We were guided by the standpoint that American philosophy is a tradition committed “to a dynamic, pluralistic world of experience in which knowledge is a... (shrink)

The “problem of intentionality” from the vantage point of a representational understanding of mind is explaining what thoughts and beliefs are and how they guide behaviour. From an anti-representationalist perspective, on the other hand, on which cognition itself is taken to be a kind of action, intentionality is a capacity to engage in behaviour that is meaningfully directed toward or about some situation. That these are not in fact competing insights is obscured by the representational/anti-representational framing of the debate. This (...) paper begins the work of shifting the conversation in two ways: (1) by arguing that it is the commitment to internal representations, not the acknowledgement of a role for representation per se, that is problematic; and, (2) by describing an alternative, externalist, representational approach that draws on extended, embodied, enactive insights. (shrink)

This book is a major contribution to the philosophical literature on the nature of the self, personal identity and survival. Its distinctive methodology is one that is phenomenologically descriptive rather than metaphysical and normative. On the basis of this approach Raymond Martin shows that the distinction between self and other is not nearly as fundamental a feature of our so-called egoistic values as has been traditionally thought. He explains how the belief in a self as a fixed, continuous point (...) of observation enters into our experience of ourselves and the world. He also reveals the explosive implications this thesis has for recent debates over personal identity and what matters in survival. This is the first book of analytic philosophy directly on the phenomenology of identity and survival. It builds bridges between analytic and phenomenological traditions and, thus, to open up a new field of investigation. (shrink)

Michael Kremer defines fixed-point logics of truth based on Saul Kripke’s fixed point semantics for languages expressing their own truth concepts. Kremer axiomatizes the strong Kleene fixed-point logic of truth and the weak Kleene fixed-point logic of truth, but leaves the axiomatizability question open for the supervaluation fixed-point logic of truth and its variants. We show that the principal supervaluation fixed point logic of truth, when thought of as consequence relation, is highly complex: it is not even analytic. We also (...) consider variants, engendered by a stronger notion of ‘fixed point’, and by variant supervaluation schemes. A ‘logic’ is often thought of, not as a consequence relation, but as a set of sentences – the sentences true on each interpretation. We axiomatize the supervaluation fixed-point logics so conceived. (shrink)

Jäger, G., Fixed points in Peano arithmetic with ordinals, Annals of Pure and Applied Logic 60 119-132. This paper deals with some proof-theoretic aspects of fixed point theories over Peano arithmetic with ordinals. It studies three such theories which differ in the principles which are available for induction on the natural numbers and ordinals. The main result states that there is a natural theory in this framework which is a conservative extension of Peano arithmeti.

In this paper, we study when a set-continuous operator has a fixed-point that is the intersection of a directed family. The framework of our study is the Kelley-Morse theory KMC– and the Gödel-Bernays theory GBC–, both theories including an Axiom of Choice and excluding the Axiom of Foundation. On the one hand, we prove a result concerning monotone operators in KMC– that cannot be proved in GBC–. On the other hand, we study conditions on directed superclasses in GBC– in order (...) that their intersection is a fixed-point of a set-continuous operator. Finally, we illustrate our results with a solution to the liar paradox and a construction of maximal bisimulations. (shrink)

In this paper it is shown that the intuitionistic .xed point theory equation image for α times iterated fixed points of strictly positive operator forms is conservative for negative arithmetic and equation image sentences over the theory equation image for α times iterated arithmetic comprehension without set parameters.This generalizes results previously due to Buchholz [5] and Arai [2].

Self-referential sentences have troubled our understanding of language for centuries. The most famous self-referential sentence is probably the Liar, a sentence that says of itself that it is false. The Liar Paradox has encouraged many philosophers to establish theories of truth that manage to give a proper account of the truth predicate in a formal language. Kripke’s Fixed Point Theory from 1975 is one famous example of such a formal theory of truth that aims at giving a plausible notion of (...) truth by allowing truth value gaps. However, not only the concept of truth gives rise to paradoxes. A syntactical treatment of epistemic notions like belief and knowledge leads to contradictions that very much resemble the Liar Paradox. Therefore, it seems to be fruitful to apply the established theories of truth to epistemic concepts. In this paper, I will present one such attempt of solving the epistemic paradoxes: I adapt Kripke’s Fixed Point Theory and interpret truth, knowledge and belief within the framework of a partial logic. Thereby I find not only the fixed point of truth but also the fixed points of knowledge and belief. In this fixed point, the predicates of truth, belief and knowledge find their definite interpretation and the paradoxes are avoided. (shrink)

In the context of his theory of numberings, Ershov showed that Kleene's recursion theorem holds for any precomplete numbering. We discuss various generalizations of this result. Among other things, we show that Arslanov's completeness criterion also holds for every precomplete numbering, and we discuss the relation with Visser's ADN theorem, as well as the uniformity or nonuniformity of the various fixed point theorems. Finally, we base numberings on partial combinatory algebras and prove a generalization of Ershov's theorem in this context.

The problem of Uniqueness and Explicit Definability of Fixed Points for Interpretability Logic is considered. It turns out that Uniqueness is an immediate corollary of a theorem of Smoryński.

We analyze the flow into inflation for generic "single-clock" systems, by combining an effective field theory approach with a dynamical-systems analysis. In this approach, we construct an expansion for the potential-like term in the effective action as a function of time, rather than specifying a particular functional dependence on a scalar field. We may then identify fixed points in the effective phase space for such systems, order-by-order, as various constraints are placed on the Mth time derivative of the (...) potential-like function. For relatively simple systems, we find significant probability for the background spacetime to flow into an inflationary state, and for inflation to persist for at least 60 efolds. Moreover, for systems that are compatible with single-scalar-field realizations, we find a single, universal functional form for the effective potential, $V$, which is similar to the well-studied potential for power-law inflation. We discuss the compatibility of such dynamical systems with observational constraints. (shrink)

Cuneo and Shafer-Landau have argued that there are moral conceptual truths that are substantive and non-vacuous in content, what they called ‘moral fixed points’. If the moral proposition ‘torturing kids for fun is pro tanto wrong’ is such a conceptual truth, it is because the essence of ‘wrong’ necessarily satisfies and applies to the substantive content of ‘torturing kids for fun’. In critique, Killoren :165–173, 2016) has revisited the old skeptical ‘why be moral?’ question and argued that the moral fixed (...) points give us no reason to care about morality and, therefore, they are normatively irrelevant. He concluded that this is a counterintuitive implication that undermines the proposal. In this paper, I develop a rejoinder to Killoren’s argument that explains why, at least from the perspective of the moral fixed points framework, if the moral fixed points exist, they are necessarily normatively relevant for rational agents. I supplement this explanation with an explanation of why it might prima facie appear that moral fixed points are not normatively relevant, although ultima facie they are relevant. The supplementary explanation explains prima facie normative irrelevance as the upshot of failures of rational agency. I conclude that the moral fixed points, can, in principle, offer an interesting response to the skeptical ‘why be moral?’ question’. (shrink)

The semantic paradoxes are associated with self-reference or referential circularity. However, there are infinitary versions of the paradoxes, such as Yablo's paradox, that do not involve this form of circularity. It remains an open question what relations of reference between collections of sentences afford the structure necessary for paradoxicality -- these are the so-called "dangerous" directed graphs. Building on Rabern, et. al (2013) we reformulate this problem in terms of fixed points of certain functions, thereby boiling it down to get (...) a purely mathematical problem. (shrink)

This article defends the Fixed Point Thesis: that it is always a rational mistake to have false beliefs about the requirements of rationality. The Fixed Point Thesis is inspired by logical omniscience requirements in formal epistemology. It argues to the Fixed Point Thesis from the Akratic Principle: that rationality forbids having an attitude while believing that attitude is rationally forbidden. It then draws out surprising consequences of the Fixed Point Thesis, for instance that certain kinds of a priori justification are (...) indefeasible and that misleading all-things-considered evidence about rational requirements is impossible. Finally, the Fixed Point Thesis is applied to defend the Right Reasons position on peer disagreement, according to which an agent who has drawn the correct conclusion from her evidence should retain belief in that conclusion even in the face of disagreeing peers. (shrink)

In this paper I argue that it’s impossible for there to be a single universal theory of meaning for a language. First, I will consider some minimal expressiveness requirements a language must meet to be able to express semantic claims. Then I will argue that in order to have a single unified theory of meaning, these expressiveness requirements must be satisfied by a language which the semantic theory itself applies to. That is, we would need a language which can express (...) its own meaning. It has been well-known since Tarski that theories of meaning whose central notion is truth can’t be expressed in a language which they apply to. Here, I develop Quine’s formulation of the Liar Paradox in grammatical terms and use this to extend Tarski’s result to all theories of meaning. This general version of the paradox can be formalised as a special case of the Lawvere Fixed-Point Theorem applied to a categorial grammar. Taken together with the initial arguments, I infer that a universal theory of meaning is impossible and conclude the paper with a brief discussion on what alternatives are available. (shrink)

We consider fixed point logics, i.e., extensions of first order predicate logic with operators defining fixed points. A number of such operators, generalizing inductive definitions, have been studied in the context of finite model theory, including nondeterministic and alternating operators. We review results established in finite model theory, and also consider the expressive power of the resulting logics on infinite structures. In particular, we establish the relationship between inflationary and nondeterministic fixed point logics and second order logic, and we consider (...) questions related to the determinacy of games associated with alternating fixed points. (shrink)

This paper deals with the modal logics associated with (possibly nonstandard) provability predicates of Peano Arithmetic. One of our goals is to present some modal systems having the fixed point property and not extending the Gödel-Löb system GL. We prove that, for every has the explicit fixed point property. Our main result states that every complete modal logic L having the Craig's interpolation property and such that , where and are suitable modal formulas, has the explicit fixed point property.

The problem of Uniqueness and Explicit Definability of Fixed Points for Interpretability Logic is considered. It turns out that Uniqueness is an immediate corollary of a theorem of Smoryski.

When we are faced with a choice among acts, but are uncertain about the true state of the world, we may be uncertain about the acts’ “choiceworthiness”. Decision theories guide our choice by making normative claims about how we should respond to this uncertainty. If we are unsure which decision theory is correct, however, we may remain unsure of what we ought to do. Given this decision-theoretic uncertainty, meta-theories attempt to resolve the conflicts between our decision theories...but we may be (...) unsure which meta-theory is correct as well. This reasoning can launch a regress of ever-higher-order uncertainty, which may leave one forever uncertain about what one ought to do. There is, fortunately, a class of circumstances under which this regress is not a problem. If one holds a cardinal understanding of subjective choiceworthiness, and accepts certain other criteria, one’s hierarchy of metanormative uncertainty ultimately converges to precise definitions of “subjective choiceworthiness” for any finite set of acts. If one allows the metanormative regress to extend to the transfinite ordinals, the convergence criteria can be weakened further. Finally, the structure of these results applies straightforwardly not just to decision-theoretic uncertainty, but also to other varieties of normative uncertainty, such as moral uncertainty. (shrink)

In Aczel [1], the existence of largest fixed points of set continuous operators is proved assuming the schema version of dependent choices in Zermelo-Fraenkel set theory without the axiom of Foundation. In the present paper, we study whether the existence of largest fixed points of set continuous operators is provable without the schema version of dependent choices, using Boffa's weak antifoundation axioms.

We prove a definable analogue to Brouwer's Fixed Point Theorem for o-minimal structures of real closed field expansions: A continuous definable function mapping from the unit simplex into itself admits a fixed point, even though the underlying space is not necessarily topologically complete. Our proof is direct and elementary; it uses a triangulation technique for o-minimal functions, with an application of Sperner's Lemma.