Let Con↾x denote the finite consistency statement “there are no proofs of contradiction in T with ≤x symbols.” For a large class of natural theories T, Pudlák has shown that the lengths of the shortest proofs of Con↾n in the theory T itself are bounded by a polynomial in n. At the same time he conjectures that T does not have polynomial proofs of the finite consistency statements Con)↾n. In contrast, we show that Peano arithmetic has polynomial proofs of Con)↾n, (...) where Con∗ is the slow consistency statement for Peano arithmetic, introduced by S.-D. Friedman, Rathjen, and Weiermann. We also obtain a new proof of the result that the usual consistency statement Con is equivalent to ε0 iterations of slow consistency. Our argument is proof-theoretic, whereas previous investigations of slow consistency relied on nonstandard models of arithmetic. (shrink)

A central question in the history of metaphysics concerns the ontological status of such notions as 'redness,' 'humanity,' or 'animality,' which one calls 'universals.' Since one uses these notions to describe objects in the real world, it may seem intuitive that they exist in extramental reality: one says that universals are 'real'. Famously, though, several problems arise from this view. A central problem known both to medieval and contemporary scholars goes as follows: I look at a red rose and recognize (...) that there is 'redness' in it. Then, I look at a red apple and recognize that there is 'redness' in it, too. Does this mean that one and the same 'redness' appears in both the rose and the... (shrink)

Essentialism can be defined as a metaphysical theory according to which things have essential and accidental properties. In this paper, I will address Avicennian essentialism, that is, essentialism...

RésuméQuels sont les objets de la perception? Deux réponses célèbres à cette question soutiennent que ce sont soit les images des objets extramentaux, c'est-à-dire la façon dont ils nous apparaissent, soit les objets eux-mêmes. Dans cet article, je présente une analyse de cette question par Abū l-Barakāt al-Baġdādī, un savant post-avicennien dont l'impact sur l'histoire de la philosophie islamique a été largement négligé. Abū l-Barakāt s'est opposé au dualisme épistémologique traditionnel aristotélicien-avicennien, qui établit une distinction entre la perception sensorielle des (...) particuliers matériels et la conception des universaux immatériels, notamment en ce qui concerne le percevant et/ou la structure de la perception. Selon la théorie d'Abū l-Barakāt, tous les actes épistémiques ont la structure unifiée d'une relation directe entre un même percevant et les objets eux-mêmes – matériels et immatériels. Sa thèse principale consiste à dire qu'avoir des organes corporels n'est pas nécessaire pour la perception sensorielle. Dans la dernière section de cet article, je montre que la critique d'Abū l-Barakāt de la tradition aristotélicienne-avicennienne fut considérée comme une innovation révolutionnaire en épistémologie. Cela peut avoir déterminé les théories épistémologiques de deux des philosophes arabes postavicenniens les plus importants : Faḫr al-Dīn al-Rāzī et Šihāb al-Dīn al-Suhrawardī. (shrink)

En estos tres artículos, que aparecen por primera vez en castellano, bosqueja el autor junto a una teoría general de la representación política, una relectura del problema permanente de la clasificación de los regímenes. Destaca en ellos particularmente el tratamiento de la cuestión de las causas de la corrupción de todas las formas de gobierno, incluida la democracia. Maquiaveliano riguroso y consciente, Freund no esquiva ninguno de los grandes problemas que siguen dividiendo hoy a quienes se acercan -no siempre (...) libres de prejuicios- a la realidad tantas veces poco complaciente de la política. (shrink)

One of the most widespread claims combining epistemology and metaphysics in post-Avicennian Islamic philosophy was that every object of thought is real. In Muʿtazilite reading, it was endorsed due to a theory of knowledge which states that knowledge is a connection or relation between the knower and the object known. Avicennists accepted it due to the rule that in a proposition “s is p” if p is something positive s has to be positive and real too. Hence, insofar as one (...) can conceptually distinguish between two non-existent items, they have to be real. In this article, the author presents significant consequences of this theory: the acceptance and denial of non-existent yet real extramental objects; the concept of mental existence as an alternative solution; the conceivability of paraconsistent ideas and their reality or reducibility to some real objects. (shrink)

ABSTRACTScholarship on medieval philosophy has rightfully acknowledged the historical and systematical merit of Avicenna’s thought in all divisions of philosophy. Avicenna however did not...

It is well-known that natural axiomatic theories are well-ordered by consistency strength. However, it is possible to construct descending chains of artificial theories with respect to consistency strength. We provide an explanation of this well-orderedness phenomenon by studying a coarsening of the consistency strength order, namely, the$\Pi ^1_1$reflection strength order. We prove that there are no descending sequences of$\Pi ^1_1$sound extensions of$\mathsf {ACA}_0$in this ordering. Accordingly, we can attach a rank in this order, which we call reflection rank, to any$\Pi (...) ^1_1$sound extension of$\mathsf {ACA}_0$. We prove that for any$\Pi ^1_1$sound theoryTextending$\mathsf {ACA}_0^+$, the reflection rank ofTequals the$\Pi ^1_1$proof-theoretic ordinal ofT. We also prove that the$\Pi ^1_1$proof-theoretic ordinal of$\alpha $iterated$\Pi ^1_1$reflection is$\varepsilon _\alpha $. Finally, we use our results to provide straightforward well-foundedness proofs of ordinal notation systems based on reflection principles. (shrink)

Many social epistemologists suggest that testimonies may be considered a valid source of knowledge, no less than, for instance, direct observation. In this article, I will focus on the accounts of testimonial knowledge in classical kalām and Islamic law. I will present the arguments for why Islamic philosophers and jurists believe that testimonies convey knowledge. I will address the main disagreement in Islamic philosophy regarding the nature of testimonial knowledge, whether we can apply an internalist model of epistemic justification to (...) testimonial knowledge or not. I will suggest that the best way to understand the traditional view on testimonial knowledge in Islamic philosophy and law is as “weak testimonial reliabilism”: testimonial knowledge typically results from the occurrence of certain external conditions (of which we might be unaware), even though they hold only insofar as our experience of this world tells us so, and may not hold in another possible world. (shrink)

Sortal concepts are at the center of certain logical discussions and have played a significant role in solutions to particular problems in philosophy. Apart from logic and philosophy, the study of sortal concepts has found its place in specific fields of psychology, such as the theory of infant cognitive development and the theory of human perception. In this monograph, different formal logics for sortal concepts and sortal-related logical notions are characterized. Most of these logics are intensional in nature and possess, (...) in addition, a bidimensional character. That is, they simultaneously represent two different logical dimensions. In most cases, the dimensions are those of time and natural necessity, and, in other cases, those of time and epistemic necessity. Another feature of the logics in question concerns second-order quantification over sortal concepts, a logical notion that is also represented in the logics. Some of the logics adopt a constant domain interpretation, others a varying domain interpretation of such quantification. Two of the above bidimensional logics are philosophically grounded on predication sortalism, that is, on the philosophical view that predication necessarily requires sortal concepts. Another bidimensional logic constitutes a logic for complex sortal predicates. These three sorts of logics are among the important novelties of this work since logics with similar features have not been developed up to now, and they might be instrumental for the solution of philosophically significant problems regarding sortal predicates. The book assumes a modern variant of conceptualism as a philosophical background. For this reason, the approach to sortal predicates is in terms of sortal concepts. Concepts, in general, are here understood as intersubjective realizable cognitive capacities. The proper features of sortal concepts are determined by an analysis of the main features of sortal predicates. Posterior to this analysis, the sortal-related logical notions represented in the above logics are discussed. There is also a discussion on the extent to which the set-theoretic formal semantic systems of the book capture different aspects of the conceptualist approach to sortals. These different semantic frameworks are also related to realist and nominalist approaches to sortal predicates, and possible modifications to them are considered that might represent those alternative approaches. (shrink)

We consider the well-known provability logic GLP. We prove that the GLP-provability problem for polymodal formulas without variables is PSPACE-complete. For a number n, let L0n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${L^{n}_0}$$\end{document} denote the class of all polymodal variable-free formulas without modalities ⟨n⟩,⟨n+1⟩,...\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\langle n \rangle,\langle n+1\rangle,...}$$\end{document}. We show that, for every number n, the GLP-provability problem for formulas from L0n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${L^{n}_0}$$\end{document} (...) is in PTIME. (shrink)

Journal of Mathematical Logic, Volume 23, Issue 02, August 2023. In mathematical logic there are two seemingly distinct kinds of principles called “reflection principles.” Semantic reflection principles assert that if a formula holds in the whole universe, then it holds in a set-sized model. Syntactic reflection principles assert that every provable sentence from some complexity class is true. In this paper, we study connections between these two kinds of reflection principles in the setting of second-order arithmetic. We prove that, for (...) a large swathe of theories, [math]-model reflection is equivalent to the claim that arbitrary iterations of uniform [math] reflection along countable well-orderings are [math]-sound. This result yields uniform ordinal analyzes of theories with strength between [math] and [math]. The main technical novelty of our analysis is the introduction of the notion of the proof-theoretic dilator of a theory [math], which is the operator on countable ordinals that maps the order-type of [math] to the proof-theoretic ordinal of [math]. We obtain precise results about the growth of proof-theoretic dilators as a function of provable [math]-model reflection. This approach enables us to simultaneously obtain not only [math], [math] and [math] ordinals but also reverse-mathematical theorems for well-ordering principles. (shrink)

In this article the author holds that progress in philosophy is a vague concept. Its criteria are not universally acknowledged. All that is clear is that philosophy does not develop in a linear way. Philosophy is polydiscoursive. As for the past fifty years, the author believes three important things happened in philosophy. (1) It has been shown that consciousness exists not within one individual but spreads within a community of people; (2) philosophy has discovered autism, a result that helps us (...) to understand a human being as neither a biological nor a social individual but a third thing—a dreaming being who is not only asocial but also tongueless, where speech and consciousness are separated; and (3) contemporary philosophy has learned to distinguish between sign and symbol. And it has been realized that the human mind is neither an instinct nor a computer but an objectified suffering, a transformed emotion. (shrink)

A short report on the trip to India.--Philosophical doctrine of Buddhism.--Logic in ancient India.--The doctrine of categorical imperative in the Brāhmaṇas.

Avicenna's analysis of the definition of substance and accident repeatedly emphasizes two points: one and the same essence cannot be substance in one instance and accident in another; whetherxis extrinsic or intrinsic for an underlying subject,ydoes not tell us anything as to whetherxis substance or not. Both points are development in an argument against certain unnamed people who claimed the opposite. In this article I will show that Avicenna's opponents are to be identified with the mainstream Baghdad Peripatetic School which (...) based itself on the Late Antique rule that “parts of substances are substances”. As for Avicenna's own position, it was developed on the basis of the heterodox position of Yaḥyā b. ʿAdī, who anticipated Avicenna's first point. This is a further piece of evidence for something that has only recently begun to be appreciated: the influence of Ibn ʿAdī on Avicenna.RésuméL’analyse d’Avicenne portant sur les définitions de la substance et de l’accident met en exergue les deux propositions suivantes: 1) la même essence ne peut être à la fois une substance dans un cas et un accident dans un autre; 2) le fait quexsoit extrinsèque ou intrinsèque à unysous-jacent ne nous permet pas de conclure quexest une substance. Ces deux propositions sont articulées dans un débat avec d’autres personnes ayant un point de vue opposé dont on ne connaît pas l’identité. Dans cet article, nous verrons que ces adversaires font partie de l’école péripatétique de Bagdad, qui elle-même s’appuie sur une proposition datant de l’Antiquité tardive et selon laquelle les parties de substances sont elles-mêmes des substances. La position d’Avicenne fut développée à partir de celle de Yaḥyā b. ʿAdī. Cet article apporte ainsi un argument nouveau qui met en évidence l’influence, remarquée seulement depuis peu, d’Ibn ʿAdī sur Avicenne. (shrink)

This is a translation of an article which appeared in 1928 in the journal Red Virgin Soil (Krasnaya nov) founded by Aleksandr Voronsky. Its author, the Russian Marxist Fedor Kapelusz, makes use of the now largely-ignored book of Algie Simons, Social Forces in American History (1911). In comparing America’s past to its present, Kapelusz offers a sharp political assessment and at the same time a contribution to the materialist conception of American history.

In a recent paper by M. Rathjen and the present author it has been shown that the statement “every normal function has a derivative” is equivalent to $\Pi ^1_1$ -bar induction. The equivalence was proved over $\mathbf {ACA_0}$, for a suitable representation of normal functions in terms of dilators. In the present paper, we show that the statement “every normal function has at least one fixed point” is equivalent to $\Pi ^1_1$ -induction along the natural numbers.

"À son décès, Julien Freund laissait parmi ses papiers un recueil de textes inédits, sous forme épistolaire, adressés à ses amis et collègues : les Lettres de la vallée. Dans ces méditations, rédigées en sa retraite vosgienne - qui n'est pas sans évoquer la Hütte de Heidegger, de l'autre côté du Rhin - et loin des servitudes propres aux écrits universitaires, l'auteur de L'Essence du politique s'exprime en toute liberté, à bâtons rompus, sur ses sujets de prédilection (le politique, (...) l'idéologie, la guerre, les totalitarismes, l'utopie, la décadence), mais également l'enseignement, le journalisme, la connaissance, le droit, la morale, la métaphysique, les limites... Ce livre forme la clef de voûte où se rejoignent les grands thèmes de sa pensée."--Page 4 de la couverture. (shrink)

In _Essentialität und Notwendigkeit: Avicenna und die Aristotelische Tradition_ stellt Fedor Benevich Avicennas Theorie der Essenz und der wissenschaftlichen Bestimmung essentieller und notwendiger Attribute in einem historischen Kontext der aristotelischen Tradition. In _Essentialität und Notwendigkeit: Avicenna und die Aristotelische Tradition_ Fedor Benevich presents Avicenna’s theory of essence and the scientific determination of essential and necessary attributes in its historical context of the Aristotelian tradition.

We shall distinguish between sortal predication and standard predication. The former kind of predication necessarily involves sortal concepts but the latter, as it is customarily viewed, does not. It is generally thought that the only essential occurrence of a concept in a standard predication is the concept being predicated. In this paper, we shall put forward an alternative view. We shall propose to understand standard predication as a cognitive act essentially requiring sortal concepts. We shall call this view conceptual predication (...) sortalism and ground it on the basis of epistemic-semantic reasons. Concepts are understood as intersubjectively realizable capacities or abilities that fulfill particular cognitive roles, such as those of classification, categorization, individuation, and referring. (shrink)

Michael Rathjen and the present author have shown that ‐bar induction is equivalent to (a suitable formalization of) the statement that every normal function has a derivative, provably in. In this note we show that the base theory can be weakened to. Our argument makes crucial use of a normal function f with and. We shall also exhibit a normal function g with and.

In the context of reverse mathematics, effective transfinite recursion refers to a principle that allows us to construct sequences of sets by recursion along arbitrary well orders, provided that each set is ‐definable relative to the previous stages of the recursion. It is known that this principle is provable in. In the present note, we argue that a common formulation of effective transfinite recursion is too restrictive. We then propose a more liberal formulation, which appears very natural and is still (...) provable in. (shrink)

We have previously established that [Formula: see text]-comprehension is equivalent to the statement that every dilator has a well-founded Bachmann–Howard fixed point, over [Formula: see text]. In this paper, we show that the base theory can be lowered to [Formula: see text]. We also show that the minimal Bachmann–Howard fixed point of a dilator [Formula: see text] can be represented by a notation system [Formula: see text], which is computable relative to [Formula: see text]. The statement that [Formula: see text] (...) is well founded for any dilator [Formula: see text] will still be equivalent to [Formula: see text]-comprehension. Thus, the latter is split into the computable transformation [Formula: see text] and a statement about the preservation of well-foundedness, over a system of computable mathematics. (shrink)

According to the restructuring hypothesis, insight problem solving typically progresses through consecutive stages of search, impasse, insight, and search again for someone, who solves the task. The order of these stages was determined through self-reports of problem solvers and has never been verified behaviorally. We asked whether individual analysis of problem solving attempts of participants revealed the same order of problem solving stages as defined by the theory and whether their subjective feelings corresponded to the problem solving stages they were (...) in. Our participants tried to solve the Five-Square problem in an online task, while we recorded the time and trajectory of their stick movements. After the task they were asked about their feelings related to insight and some of them also had the possibility of reporting impasse while working on the task. We found that the majority of participants did not follow the classic four-stage model of insight, but had more complex sequences of problem solving stages, with search and impasse recurring several times. This means that the classic four-stage model is not sufficient to describe variability on the individual level. We revised the classic model and we provide a new model that can generate all sequences found. Solvers reported insight more often than non-solvers and non-solvers reported impasse more often than solvers, as expected; but participants did not report impasse more often during behaviorally defined impasse stages than during other stages. This shows that impasse reports might be unreliable indicators of impasse. Our study highlights the importance of individual analysis of problem solving behavior to verify insight theory. (shrink)

A. Tarski [22] proposed the study of infinitary consequence operations as the central topic of mathematical logic. He considered monotonicity to be a property of all such operations. In this paper, we weaken the monotonicity requirement and consider more general operations, inference operations. These operations describe the nonmonotonic logics both humans and machines seem to be using when infering defeasible information from incomplete knowledge. We single out a number of interesting families of inference operations. This study of infinitary inference operations (...) is inspired by the results of [12] on nonmonotonic inference relations, and relies on some of the definitions found there. (shrink)

We show that arithmetical transfinite recursion is equivalent to a suitable formalization of the following: For every ordinal \alpha there exists an ordinal /beta such that 1 + \beta \cdot (\beta + \alpha) admits an almost order preserving collapse into \beta. Arithmetical comprehension is equivalent to a statement of the same form, with \beta \cdot \alpha at the place of \beta \cdot (\beta + \alpha). We will also characterise the principles that any set is contained in a countable coded ω-model (...) of arithmetical transfinite recursion and arithmetical comprehension, respectively. (shrink)

When a proposition is cumulatively entailed by a finite setA of premisses, there exists, trivially, a finite subsetB ofA such thatB B entails for all finite subsetsB that are entailed byA. This property is no longer valid whenA is taken to be an arbitrary infinite set, even when the considered inference operation is supposed to be compact. This leads to a refinement of the classical definition of compactness. We call supracompact the inference operations that satisfy the non-finitary analogue of the (...) above property. We show that for any arbitrary cumulative operationC, there exists a supracompact cumulative operationK(C) that is smaller thenC and agrees withC on finite sets. Moreover,K(C) inherits most of the properties thatC may enjoy, like monotonicity, distributivity or disjunctive rationality. The main part of the paper concerns distributive supracompact operations. These operations satisfy a simple functional equation, and there exists a representation theorem that provides a semantic characterization for this family of operations. We examine finally the case of rational operations and show that they can be represented by a specific kind of model particularly easy to handle. (shrink)

We fix a gap in a proof in our paper Reducing ω-model reflection to iterated syntactic reflection.

In this paper, we study finitely axiomatizable conservative extensions of a theoryUin the case whereUis recursively enumerable and not finitely axiomatizable. Stanisław Krajewski posed the question whether there are minimal conservative extensions of this sort. We answer this question negatively.Consider a finite expansion of the signature ofUthat contains at least one predicate symbol of arity ≥ 2. We show that, for any finite extensionαofUin the expanded language that is conservative overU, there is a conservative extensionβofUin the expanded language, such that$\alpha (...) \vdash \beta$and$\beta \not \vdash \alpha$. The result is preserved when we consider eitherextensionsormodel-conservative extensionsofUinstead ofconservative extensions. Moreover, the result is preserved when we replace$\dashv$as ordering on the finitely axiomatized extensions in the expanded language by a relevant kind of interpretability, to witinterpretability that identically translates the symbols of the U-language.We show that the result fails when we consider an expansion with only unary predicate symbols for conservative extensions ofUordered by interpretability that preserves the symbols ofU. (shrink)

The article attempts to explain the difficulty of systematization of philosophical categories. Philosophical categories are defined as common forms of cognitive and world view attitude of the man to the nature, society and his own existence. The article also analyses basic approaches to the process of creating the system of philosophical categories in the history of philosophical thought. The review of the major historical phases of philosophical interpretation of categories allows to state the existence of the problematic issue connected with (...) forming the system of categories. A lot of attempts have been undertaken on this subject. All of them were found controversial. It can be explained by the fact that all the attempts to systematize categories contradict the following principles - if categories are universal reflection forms of objective characteristics of existence, then their hierarchy must be the reflection of these characteristics’ hierarchy. But it is impossible to imagine that the "hierarchy" principle operates in the system of being, because the objective world is organized rather on the principle of "equality" than "subordination". The article addresses functional and developmental characteristics of philosophical categories. The article gives the author`s understanding of the concept of "philosophical categories". (shrink)

It has been questioned whether it is at all possible to give the term “probability” one uniform and consistent interpretation not merely in mathematics, statistics, evaluation of evidence, testing of hypotheses but also in any situation where we want to express a degree of belief. The question itself of assigning a probability to our belief in a scientific theory has raised important questions of an epistemological as well as mathematical nature.