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This paper presents the link between Arthur N. Prior and logicians that belonged to the Lvov-Warsaw School. Although certain members of the Lvov-Warsaw School influenced Prior's views, the amount and the form of the impact are still under discussion. Prior also cooperated with some of them in the development of his systems of logic. This paper focuses on four main areas in which Prior admitted adopting ideas from the Lvov-Warsaw School: systems of propositional logic, the history of logic, modal and temporal logic and ontology. Prior's published works as well as his correspondence, which is stored in Prior's Nachlass, are used to describe the influence. [ABSTRACT FROM AUTHOR]

In the Handbook of Mathematical Logic, the Paris-Harrington variant of Ramsey's theorem is celebrated as the first result of a long 'search' for a purely mathematical incompleteness result in first-order Peano arithmetic. This paper questions the existence of any such search and the status of the Paris-Harrington result as the first mathematical incompleteness result. In fact, I argue that Gentzen gave the first such result, and that it was restated by Goodstein in a number-theoretic form. [ABSTRACT FROM AUTHOR]

This paper sketches the antilogism of Christine Ladd-Franklin and historical advancement about antilogism, mainly constructs an axiomatic system Atl based on first-order logic with equality and the wholly-exclusion and not-wholly-exclusion relations abstracted from the algebra of Ladd-Franklin, with soundness and completeness of Atl proved, providing a simple and convenient tool on syllogistic reasoning. Atl depicts the empty class and the whole class differently from normal set theories, e.g. ZFC, revealing another perspective on sets and set theories. Two series of Dotterer and the theorem proved by Russinoff are re-characterized in antilogistic formulas corresponding to the square of opposition and twenty-four moods of syllogism. Then the restricted equivalence between two forms of antilogism and minimal inconsistency is built up, implying the internal connection between antilogisms and minimal inconsistency and leaving two related conjectures not proved. Besides, this paper provides a new explanation for the reason why contrariety, subcontrariety, and subalternation and the nine special moods require the non-empty assumption. [ABSTRACT FROM AUTHOR]

Recently, in 'An inquiry on Fakhr al-Dīn Rāzī's authorship of Al-manṭiq al-kab $ \bar{\iota} $ ι ¯ r (MS Aḥmad iii, no. 3401)', we refuted the quite common view among historians of Arabic logic as to attribute Al-manṭiq al-kab $ \bar{\iota} $ ι ¯ r (Major [book on] logic) to Fakhr al-dīn Rāzī; however, in that paper, we could not identify the real author of the book. In this paper, we try to show that Al-manṭiq al-kab $ \bar{\iota} $ ι ¯ r was written by Burhān al-dīn Nasafī (1203–1288), who authored another book, Sharḥ Asās al-kiyāsa whose logical part is very similar to Al-manṭiq al-kab $ \bar{\iota} $ ι ¯ r in the following significant features: the titles of chapters and sections, the style of writing, some technical as well as some non-technical terms, many sentences word by word. None of these features we find in any other Arabic logical work. So, Al-manṭiq al-kab $ \bar{\iota} $ ι ¯ r and Sharḥ Asās al-kiyāsa are so close to each other that we might most possibly identify the authors of the books as the same scholar, i.e. Burhān al-dīn Nasafī. Fortunately, this has been verified recently by two manuscripts of a medieval Arabic logical book. [ABSTRACT FROM AUTHOR]

Justification of theorems plays a vital role in any rational human activity. It is indispensable in science. The deductive method of justifying theorems is used in all sciences and it is the only method of justifying theorems in deductive disciplines. It is based on the notion of proof, thus it is a method of proving theorems. In the Warsaw School of Logic (WSL) – the famous branch of the Lvov-Warsaw School (LWS) – two types of the method: axiomatic deduction method and natural deduction method were developed and practiced. In this paper, both of these methods are briefly discussed with an emphasis on their historical, groundbreaking significance for logic. The axiomatic method by means of rejection (proposed by Jan Łukasiewicz – a co-creator of the WSL), which is the method of the so-called rejection proof (rejection/refutation method) in logical systems and the proving method of generalized natural deduction, which is a hybrid deduction–refutation method of proving theorems, are also outlined in the paper. The author discusses their historical significance. This paper also contains a brief mention of the most significant results which the application of the discussed methods introduced into contemporary scientific research, not only logical one. [ABSTRACT FROM AUTHOR]

Łukasiewicz introduced a new methodological approach to the history of logic. It consists of the use of modern formal logic in the research of the history of logic. Although he was not the first to use formal logic in his historical research, Łukasiewicz was the first who used it consistently and formulated it as a requirement for a historian of logic. The aim of this paper is to present Łukasiewicz's contribution and the history of its formulation. In addition, the paper will present its reception. There are two main themes in Łukasiewicz's work on the history of logic. He discussed Stoic logic and Aristotle's syllogistic. The second part of the paper focuses on current reception of Łukasiewicz's contribution and on the question of whether there is a difference between knowledge about his contribution to Stoic logic and to Aristotle's syllogistic, given that it has been hypothesised that Łukasiewicz's contribution is currently more known among Aristotelian scholars than among those who focus on Stoic logic. Based on the papers that have appeared in the last five years at Web of Science and Scopus this hypothesis has not been confirmed. [ABSTRACT FROM AUTHOR]

We take into account two areas of the logical research of the Lvov-Warsaw School. First, we consider a new approach to research in the history of logic introduced and practiced by Łukasiewicz and some of his followers. In this style of doing history of logic, the knowledge of original philosophical and logical texts was combined with competence in modern logic. This method resulted in many important discoveries both in history and in logic and philosophy. At the same time, we pay attention to contemporary historical research devoted to the logic created by the School itself. In this context, we present an overview of the six papers included in the special issue 'Logic and its History in the Lvov-Warsaw School'. These papers were presented at an international symposium, 'History in/of the Lvov-Warsaw School', held in October 2022 in Warsaw, and they cover various aspects of historical-logical and logical achievements of the School. They concern topics from history of ancient logic, history of modern proof theory, and the issues of applying logic to philosophy and theology in the same way as the one implemented at the Lvov-Warsaw School. [ABSTRACT FROM AUTHOR]

The paper explores the potential of Byzantine diagrams in syllogistic logic. Byzantine diagrams are originated by Byzantine scholars in the early modern period to use as tools for teaching and studying Aristotelian logic. This paper presents pioneering work on employing Byzantine diagrams for checking syllogistic validity through reduction. [ABSTRACT FROM AUTHOR]

The aim of this paper is to look at the arguments advanced by three Parisian arts masters about how to understand Prior Analytics II 4 and the more general discussion that medieval authors situate this in, revolving around the validity of various rules of inference. In particular, this paper argues that all three arts masters read Aristotle's remarks as committing him to a weak form of connexive principles where the antecedent needs to be either true or at least formally possible; this is known in the contemporary literature as a weak connexive thesis. [ABSTRACT FROM AUTHOR]

The paper is about the connection between logic and discrimination, with special focus on Plumwood's ideas in her groundbreaking article 'The Politics of Reason. Towards a Feminist Logic' (1993). Although Plumwood's paper is not focused on the notion of discrimination, what she writes is useful for illuminating some basic mechanisms of thought that are at the basis of discriminatory practices. After an introductory section about the concepts of logic and discrimination and their possible interconnections, I present Plumwood's ideas in 1993 with a special focus on their relevance for understanding the nature of discrimination. More specifically, I use examples of discriminatory practices that make the connection between logical operations and oppression envisaged by Plumwood clear. I focus especially on two questions: Can logic produce discrimination? Can logic contribute to the fight against discrimination? If so, how? [ABSTRACT FROM AUTHOR]

The paper examines the interplays between logic and politics in the Polish School of Logic starting from 1914. The Polish School of Logic flourished between 1920 and 1939. Philosophically, it was influenced by Kazimierz Twardowski (1866–1938). For Twardowski logic is fundamental for every kind of human activity, professional and private and this means that every argument should be formulated and proceed by correct inferential rules. These rules involve semiotics, formal logic and methodology of science. The paper shows how this position was shared by Twardowski's students, including Jan Łukasiewicz, Stanisław Leśniewski, Kazimierz Ajdukiewicz and Tadeusz Kotrabiński, as well as by the next generation of logicians and philosophers and especially by Alfred Tarski. These authors considered logic, philosophy and science as completely neutral with respect to politics and ideology but they also considered logical skills as indispensable in political activities. [ABSTRACT FROM AUTHOR]

This paper aims to reassess a notion in the works of the later Husserl that is both historically important and philosophically insightful, but remains understudied, namely, that of type. In opposition to a standard reading which treats Husserl's type presentations as pre-conceptual habits, this paper argues that these representations are a specific kind of concept. More precisely, it shows that Husserl's account of type presentations is akin to the contemporary prototype theory of concepts. This is historically important, since the predecessor of the prototype theory is usually said to be Wittgenstein. From a philosophical standpoint, the paper shows that Husserl has an innovative account of the connection between type concepts and their extension. Contrary to the standard view of extensions as sets and thus sharp entities, Husserl develops a correlationalist theory of concepts, according to which, for the specific characteristics in the structure of a concept, there are corresponding characteristics in the arrangement of its members, and vice versa. According to this theory, while sharp concepts lead to sharp extensions, vague concepts such as (proto)type concepts lead to vague extensions. The paper presents this understanding of Husserl in detail and explains its philosophical significance. [ABSTRACT FROM AUTHOR]

This paper argues that there are three reasons why we should regard Wittgenstein's Tractatus as a forerunner of formal semantics: Wittgenstein is convinced that we can apply formal notions to natural languages, that the meaning of a sentence is to be explained in terms of its truth-conditions and that language is compositional. These claims are also defended against the following three objections. First, the formal semantics defines truth-conditions using the language-metalanguage distinction, while Wittgenstein doesn't. He relies on the picture theory, which is not a formal notion. Secondly, the formal semanticists' 'compositionality principle' presupposes that the truth-conditions of complex sentences should be understood in terms of the truth-conditions of elementary ones, whereas Wittgenstein applies the notion of truth-conditions only to complex sentences. And, finally, that differently from the formal semanticists, Wittgenstein doesn't envisage recursive rules for the combination of the semantic primitives. The claim of this paper is that the first objection can be overcome by relating the picture theory to the pre-Tractarian principle of bipolarity, the second by relying on the famous distinction between what a sentence says and what it shows and the third by acknowledging that Wittgenstein, differently from the formal semanticists, works with propositional logic. [ABSTRACT FROM AUTHOR]

At APr 2.4 57a36–13, Aristotle presents a notorious reductio argument in which he derives the claim 'If B is not large, B is large' and calls that result impossible. Aristotle is thus committed to some form of connexivity and this paper argues that his commitment is to a strong form of connexivity which excludes even cases in which 'B is large' is necessary. It is further argued that Aristotle's view of connexivity is best understood as arising from his analysis of affirmation and negation in terms of combination and separation: a proposition that separates two terms cannot entail a proposition that combines the same two terms. In order to motivate this account of connexivity, this paper interprets Aristotle as emphasising the predicative structure, especially the copulae, of the argument's component propositions. The arguments for this are based on a consideration of the larger context of APr 2.2–4. A reconstruction of the argument using propositional variables does not fully capture Aristotle's intentions. [ABSTRACT FROM AUTHOR]

In 1817, in the preface to his Rein analytischer Beweis, Bernard Bolzano revealed that he had decided to postpone the publication of any subsequent instalment of his Beyträge zu einer begründeteren Darstellung der Mathematik because of the few and 'superficial' reviews of its first instalment, published in 1810. Bolzano's transcriptions of the only two known reviews of this book are conserved at the Literární archiv Památníku národního písemnictví / Muzea literatury, in Prague, together with another manuscript on his Beyträge, the provenance of which was unknown to Bolzano's scholars until recently. In this paper it is shown that this latter manuscript is a draft of an announcement that was published at the time and that was indeed written at least to some extent by Bolzano himself. This hitherto unknown announcement of Bolzano's Beyträge not only solves the mystery surrounding that manuscript, but also helps to date the publication of this book more precisely and provides an unusual insight into what we must take Bolzano himself to have considered most noteworthy about his work, namely his study on logic. The paper includes a transcription of the manuscript and an English translation of the announcement. [ABSTRACT FROM AUTHOR]

This paper stresses the importance of identifying the nature of an author's conception of logic when using terms from modern logic in order to avoid, as far as possible, injecting our own conception of logic in the author's texts. Sundholm (2012. “‘Inference versus consequence” revisited: Inference, conditional, implication’, Synthese, 187, 943–956) points out that inferences are staged at the epistemic level and are made out of judgments, not propositions. Since it is now standard to read Aristotelian sullogismoi as inferences, I have taken Alexander of Aphrodisias's commentaries to Aristotle's logical treatises as a basis for arguing that the premises and conclusions should be read as judgments rather than as propositions. Under this reading, when Alexander speaks of protaseis, we should not read the modern notion of proposition, but rather what we now call judgments. The point is not just a matter of terminology, it is about the conception of logic this terminology conveys. In this regard, insisting on judgments rather than on propositions helps bring to light Alexander's epistemic conception of logic. [ABSTRACT FROM AUTHOR]

In 'Many-valued Logics', a lecture broadcast over New Zealand's public radio in 1957, Arthur N. Prior (1914–1969) complained that conjunctions are put 'to something like forced labour' in Łukasiewicz's three-valued semantics, Ł3. In this paper, we discuss what Prior might have meant by this. [ABSTRACT FROM AUTHOR]

Ṣadr al-Dīn al-Dashtakī (d. 1498) has proposed a solution to the liar paradox according to which the liar sentence is a self-referential sentence in which the predicate 'false' is iterated. Discussing the conditions for the truth-aptness of the sentences with nested and iterated instances of the predicates 'true' and/or 'false', Dashtakī argued that the liar sentence is not truth-apt at all. In the tradition of Arabic logic, the central elements of Dashtakī's solution—the self-referentiality of the liar sentence and the implicit iteration of the predicate 'false'—were initially highlighted in two earlier solutions proposed by Naṣīr al-Dīn al-Ṭūsī (d. 1274) and Shams al-Dīn al-Samarqandī (d. 1322), respectively. Here I investigate all three solutions and show that Dashtakī's solution can be taken as a synthesis of the other two. None of these solutions seems to be convincing at the end of the day. Nevertheless, all of them include significant logical and philosophical insights. In particular, although Dashtakī's solution is not itself compelling, it is only a few steps away from a promising solution. The appendix to this paper includes translations of the relevant passages. [ABSTRACT FROM AUTHOR]

My first aim in this paper is to use time diagrams in the style of Brentano to analyze constructions in Brouwer's separable mathematics more precisely. I argue that constructions must involve not only pairing and projecting as basic operations guaranteed by the intuition of twoity, as sometimes assumed in the literature, but also a recalling operation. My second aim is to argue that Brouwer's views on the intuition of twoity and arithmetic lead to an ontological explosion. Redeveloping the constructions of natural numbers and systems sketched in an appendix to Brouwer's Cambridge lectures, I observe that the only plausible way he can make some elementary arithmetic in his separable mathematics is by allowing for the same canonical number to be determined by multiple separable entities, resulting in an overabundant mathematical ontology. [ABSTRACT FROM AUTHOR]

In 1672 John Eliot, English Puritan educator and missionary to New England, published The Logick Primer: Some Logical Notions to initiate the INDIANS in the knowledge of the Rule of Reason; and to know how to make use thereof (Eliot 1672) The Logick Primer: Some Logical Notions to Initiate the INDIANS in the Knowledge of the Rule of Reason; and to Know How to Make Use Thereof , Cambridge, MA: Marmaduke Johnson]. This roughly 80 page pamphlet introduces syllogistic vocabulary and reasoning so that syllogisms can be created from Biblical texts. The use of logic for proselytizing purposes is not distinctive: What is distinctive about Eliot's book is that it is bilingual, written in both English and Massachusett (Wôpanâak), an Algonquian language spoken in eastern coastal and southeastern Massachusetts. It is one of the earliest bilingual logic textbooks and it is the first, and perhaps only, textbook in an indigenous American language. In this paper, we (1) introduce John Eliot and the linguistic context he was working in; (2) introduce the contents of the Logick Primer – vocabulary, inference patterns, and applications; (3) discuss notions of 'Puritan' logic that inform this primer; and (4) address the importance of his work in documenting and expanding the Massachusett language and the problems that accompany his colonial approach to this work. [ABSTRACT FROM AUTHOR]

Wittgenstein's conception of the general form of a truth function given in thesis 6 can be presented as a sort of a trade-off: the author of the Tractatus is unable to reconcile the simplicity of his original idea of a series of forms with the simplicity of his generalisation of Sheffer's stroke; therefore, he is forced to sacrifice one of them. As we argue in this paper, the choice he makes – to weaken the logical constraints put on the concept of a series of forms, thus effectively metaphorising that concept for the sake of upholding the N-operation's role of generating the series – is unfortunate. An actual expansion of a series of truth functions as defined in 6 would require either making decisions at each step (Anscombe) or outwardly rejecting the concept of a series (Sundholm). However, neither is faithful to Wittgenstein's own fundamental intuitions regarding the nature of logic. For this reason, a different trade-off that prioritises upholding the basic features of a series of forms over the simplicity of the operation that generates that series seems to be much more reasonable. We offer such a trade-off by developing the schema already present in the Tractatus (5.101). The key element of our alternative solution is the construction of an operation that can perform the task of producing all consecutive truth functions of a given collection of atomic propositions as an invariant difference between any base and its successor throughout the series. We define it as a composition of three functions (in an algebraic sense): the first turns a symbol of a given truth function into a binary number, the second increments that number, the third turns the result back into a symbol of another truth function. We also show how the operation can be defined by means of a different notation without invoking binary arithmetic. [ABSTRACT FROM AUTHOR]

In his famous letter to A. N. Prior dated 3 September 1958, Saul Kripke suggested the use of branching time in temporal logic. In this paper, however, it is argued that Prior worked with an idea close to the notion of branching time ('the big Y') already the year before he received Kripke's letter. It is likely that Prior's findings based on this early study can explain why Prior so quickly accepted the idea of branching time when he received Kripke's letter. [ABSTRACT FROM AUTHOR]

In this paper Venn's account of probability inference and induction is examined, tracing their differences as well as how they ‘co-operate’ in inferences from particulars to particulars. We discuss the role of mathematical idealizations in making probability inferences, the celebrated rule of succession and we delve into the nature of the reference class problem arguing that for Venn it is a common problem for both induction and inference in probability. Our approach is both historical and philosophical attempting to sketch Venn's position both in the philosophy of probability and induction of his time and in relation to the twentieth-century frequentism. [ABSTRACT FROM AUTHOR]

Over the past decades, Patricia Blanchette has developed a sophisticated account of Frege's conception of logic and his views on logical consequence. One of the central components of her interpretation is the idea that Frege's conception of logical consequence is 'semantically laden' and not purely formal. The aim of the present paper is to provide precise explications of this as well as related ideas that inform her account, and to discuss their significance for the philosophy of logic in general and Frege's philosophy in particular. [ABSTRACT FROM AUTHOR]

In contemporary works on conditionals, the Ramsey test is a procedure for the evaluation of conditional sentences. There are several versions of the test, all inspired by a footnote by the British philosopher and mathematician Frank Ramsey, in his General Propositions and Causality. However, no study on Ramsey's own account of conditionals has been put forth so far. Furthermore, the footnote seems to cover indicative conditionals only, and this has led to the belief that no account of counterfactuals can be found in Ramsey's work. In this paper, I recover Ramsey's account of counterfactuals and show that it is sketched in the footnote too. The result is a well-developed account of counterfactuals that resembles many contemporary ones. But Ramsey uses the same approach also for other types of conditionals, and this casts doubts on the current criteria for the classification of this type of sentences. [ABSTRACT FROM AUTHOR]

In his Lectures on the History of Philosophy, Hegel develops a subtle analysis of Megarian paradoxes: the Liar, the Veiled Man and the Sorites. In this paper, we focus on Hegel's interpretation of the Liar. We note that in Hegel's treatment there are positive suggestions for a new analysis of the paradox. Faced with the Liar's sentence 'µ' that says '"µ" is false', Hegel's idea is that the conjunction 'µ and not µ' is to be held true, but the two conjuncts 'µ' and 'not µ', separately taken, are untrue. Other parts of Hegel's work confirm the idea that a true contradiction for him is made of two untrue sentences, which is an interesting but unusual account of inconsistency. In this paper, we explore the plausibility of the hypothesis with the lens of the contemporary theories of paradoxes. We compare Hegel's view with standard dialetheism, and we present Hegel's idea of truth which underlies the theory. [ABSTRACT FROM AUTHOR]

The article deals with the Lutheran–Catholic religious colloquy at Regensburg of 1601. It points out that the event was of importance not only for political and religious reasons but also in terms of applied logic. Analysis of samples of the colloquy minutes proves that the overall disputation method in the Acta Colloquii Ratisbonensis consists of the Multi-thread, Asking-answering and the Objection-solving paradigmatic methods and shows in which phases of the colloquy these methods were applied. Further, with quantitative precision, the paper aims to present the colloquy as an explanation of why the phenomenon of treatises on how to dispute emerged in Europe in the first half of the seventeenth century. Within that, quarrels over burden of proof and the dialectical form at Regensburg are also explicated in detail. Finally, it is inquired whether or not there was any other religious colloquy that was more significant for the rise of the handbooks genre than the Regensburg. The paper also provides four detailed tables as a ground for various proofs and for the reader's own study. [ABSTRACT FROM AUTHOR]

We present how the theory of reasoning developed by Tadeusz Czeżowski, a Polish logician and a member of the Lvov-Warsaw School (LWS) can be applied to the mediaeval texts which interpret the Bible, which we collectively call as Biblical exegesis (BE). In the first part of the paper, we characterise Czeżowski's theory of reasoning with some modifications based on remarks of Kazimierz Ajdukiewicz. On these grounds, we discuss the nature of reasoning and its different types, as well as the problem of textual representation of reasoning. In the second part, we describe the analytical nature of some BE at the end of twelfth century and in the thirteenth century by referring to the examples of Stephen Langton, Robert Grosseteste, Bonaventure, Albert the Great and Thomas Aquinas. We argue that they represented an analytical approach in BE, characterised by advanced use of logic and specific methods, including reasoning reconstruction and logical analysis. In the third part, we present selected examples to show how Czeżowski's framework helps in identifying various types of reasoning. We indicate some universal problems with the textual representation of reasoning found in the BE of the authors in question. Lastly, we point out how Czeżowski's framework enables the understanding of phenomena such as 'Special Biblical Inference'. Thanks to this experiment, we can see how a framework as advanced as that offered by LWS representatives can be put to the test using mediaeval Biblical commentaries, yielding interesting results. [ABSTRACT FROM AUTHOR]

We classify two of Bertrand Russell's theories of events within the point-free ontology. The first of such approaches was presented informally by Russell in 'The World of Physics and the World of Sense' (Lecture IV in Our Knowledge of the External World of 1914). Based on this theory, Russell sketched ways to construct instants as collections of events. This paper formalizes Russell's approach from 1914. We will also show that in such a reconstructed theory, we obtain all axioms of Russell's second theory from 1936 and all axioms of Thomason's theory of events from 1989. Russell's work certainly influenced the works of Stanisław Leśniewski, his student Alfred Tarski, and Czesław Lejewski – prominent members of the Lvov-Warsaw School (LWS). We see our work in the tradition of the research of Leśniewski and Tarski. Building on the technical tools developed in this environment and in the spirit of the traditional research of the LWS, we engage here, in particular, with two classic works by Russell on fundamental ontology. [ABSTRACT FROM AUTHOR]

The problem of precise characterisation of traditional forms of reasoning applied in mathematics was independently investigated and successfully resolved by Jaśkowski and Gentzen in 1934. However, there are traces of earlier interests in this field exhibited by the members of the Lvov-Warsaw School. We focus on the results obtained by Jaśkowski and Leśniewski. Jaśkowski provided the first formal system of natural deduction in 1926. Leśniewski also demonstrated in some of his papers how to construct proofs in accordance with intuitively correct principles. [ABSTRACT FROM AUTHOR]

Vādanyāya is one of the representative works of Dharmakīrti. It is concerned with debate logic and deals with win-or-lose reasoning rules in the broad sense of logic. In this paper, we will concentrate our discussion on Dharmakīrti’s theory of nigrahasthāna (fault) in his debate logic, a key issue in Vādanyāya. First, we point out that the justification of three logical reasons as proof conditions of debate constitutes the rational point of departure for Dharmakīrti’s debate logic. Second, we analyze the differences between Dharmakīrti’s and the Naiyāyika’s notion of debate and point out that Dharmakīrti’s ‘debate’ involves two parties (the disputant and the opponent) attempting to rationally refute the other’s opinion to persuade the other to change their wrong ideas. Last, based on the discussion of Dharmakīrti’s concept of debate logic, we identify seven types of nigrahasthāna in Vādanyāya with regard to the two parties of a debate (the disputant and the opponent). [ABSTRACT FROM AUTHOR]

In this paper, I examine Ruth Barcan Marcus's early formal work on modal systems and the deduction theorem, both for the material and the strict conditional. Marcus proved that the deduction theorem for the material conditional does not hold for system S2 but holds for S4. This last result is at odds with the recent claim that without proper restrictions the deduction theorem fails also for S4. I explain where the contrast stems from. For the strict conditional, Marcus proved the deduction theorem for S4 though restricted to arguments with necessary premises. I discuss Marcus's result and analyze her philosophical position on the significance of the deduction theorem for modal systems designed to express the notion of deducibility. [ABSTRACT FROM AUTHOR]

In Categories 12 (14b11–22), Aristotle famously claims that [1] true sentences and reality stand in a mutually implicative relationship, and that [2] reality causes the truth of sentences but not vice versa. In this paper, I first argue that Boethius’ reading of the above passage led medieval logicians to assess [1] and [2] within the framework of a theory of consequence. Then, I consider two important questions raised by Boethius and later logicians in relation to [1] and [2], and, namely, whether the implication described in [1] really satisfies the requirement for consequence, and whether the truthmaking relation posited in [2] can be boiled down to the relation of consequence. Boethius himself, I argue, answered affirmatively to both questions and thus (much like some contemporary truthmaker theorists) committed himself to an account of truthmaking as entailment. I then consider criticisms to Boethius’ account found in the writings of William of Champeaux, two anonymous authors connected to the school of Jocelyn of Soissons, Peter Abelard, and the author of the Ars Meliduna. Here, I argue that the emergence of a concern for relevance drives the need for abandoning Boethius’ account as well as his conception of truthmaking as entailment. [ABSTRACT FROM AUTHOR]

Hegel's approach to soritical arguments (as well as to paradoxes in general) can be read as a kind of conjunctive paraconsistency: the 'explosive' effect of contradictions is avoided by assuming 'the unity of the opposites', so that contradictory conjunctions are not simplifiable. The paper reconsiders what Hegel says about the Sorites and justifies the conjunctive interpretation. The first section introduces the analysis, presenting the role of the Einheit Entgegengesetzter for contemporary theories of paradoxes. In the second section, the focus is on Hegel's interpretation of the Sorites. The third section briefly considers some contemporary accounts of vagueness in the light of Hegel's view so reconstructed. The last section summarizes the main results and explores some ideas about how to formalize a Hegel-inspired conjunctive view. [ABSTRACT FROM AUTHOR]

Gotthard Günther's early work is inspired by Hegel's logic. Both share the view that the forms of 'classical logic' are insufficient to capture essential aspects of thought. However, while Hegel rules out formalization for his dialectical logic, Günther attributes this to the fact that Hegel's thought itself is still bound to the forms of a classical logic. Günther thus develops a trans-classical logic, with which he believes he can formally capture some of Hegel's insights. The paper presents Günther's critical engagement with Hegel and outlines some basic assumptions arising from his critique. [ABSTRACT FROM AUTHOR]

I give a formal model of dialectical progression, as found in Hegel and Marx. The model is outlined in the first half of the paper, and deploys the tools of a formal paraconsistent logic. In the second half, I discuss a number of examples of dialectical progressions to be found in Hegel and Marx, showing how they fit the model. [ABSTRACT FROM AUTHOR]

The aim of this paper is to lay bare the roots of dialetheism in discussions about dialectics and dialectical logic at the time of the first development of paraconsistent logics. In other words, this essay is the attempt to write the first step of a history of dialetheism. I consider, first, the logico-philosophical terrain in which dialetheism was born: the discussions on what was called at that time 'dialectical logic' and its relation to paraconsistent logic. Second, I highlight what I define a dialectical turn in Richard Routley's thought. Third, I consider Graham Priest's arrival to Australia, which goes hand in hand with the beginning of a longstanding collaboration and friendship with Routley, and provides the conditions for the introduction of the new word at the beginning of the 1980s. I conclude with some reflections about what happens when a new word enters the philosophical world: what is made possible by the new presence? But also: what can get lost, and how can what was lost be recuperated? [ABSTRACT FROM AUTHOR]

It is quite common among historians of Arabic logic to attribute MS Aḥmad iii, no. 3401, entitled Al-manṭiq al-kabīr (Major [book on] logic), to Fakhr al-Dīn Rāzī. This view is expressed explicitly and forcefully by Franziska Knobel (2015) and Turgut Akyüz and Elmin Aliyev (2020). In this paper, we try to refute this attribution through textual analysis, thereby exposing new evidence to the contrary. We show that the text has several references to Fakhr al-Dīn Rāzī himself as well as to some later logicians such as Rāzī's pupil Zayn al-Dīn Kashshī and the latter's successor Afḍal al-Dīn Khūnajī. We also show that contrary to some contemporary historians, all references to 'kitābunā al-kabīr' ('our major book') in Rāzī's Sharḥ Al-ishārāt do not refer to Al-manṭiq al-kabīr, but to Al-mabāhith al-mashriqiyya. [ABSTRACT FROM AUTHOR]

This paper aims at disentangling two distinct problems in present philosophy of logic: the a priori/a posteriori divide and the theory choice problem. A confusion of these problems is present in the heart of current anti-exceptionalism about logic, as the use of a posteriori methods is identified with theory choice. We illustrate how the division may be preserved in a version of anti-exceptionalism by discussing Carnap's approach, which had both an a priori epistemology and a pragmatic account of logical theory choice. This contributes to illuminate the claim that the current understanding is mistaken in considering Carnap as an exceptionalist, and it also helps us to address one of the difficulties of current anti-exceptionalism, to know, that, by equating a posteriori with theory choice, it requires appeal to framework-independent facts. We suggest that the pragmatic account of both Quine and Carnap to theory choice was advanced precisely to avoid that kind of difficulty. [ABSTRACT FROM AUTHOR]

In the Laws of Thought, Boole establishes a theory of secondary propositions based upon the notion of time. This temporal interpretation of secondary propositions has historically been met with wide disapproval and is usually dismissed in the modern literature as a philosophical non-starter. What was Boole thinking? This paper attempts to give an answer to this question. Specifically, it provides an account according to which Boole's temporal interpretation follows from his psychologistic conception of logic, in addition to certain background assumptions regarding the psychological necessity of the concept of time. Once Boole's psychological premises are laid bare, it becomes clearer how he might have viewed the temporal interpretation to be an essential feature of his theory of secondary propositions. [ABSTRACT FROM AUTHOR]

Reasoning with diagrams is considered to be a peculiar form of reasoning. Diagrams are often associated with imagistic representations conveyed by spatial arrangements of lines, points, figures, or letters that can be manipulated to obtain knowledge on a subject matter. Reasoning with diagrams is not just ‘peculiar’ because reasoners use spatially arranged characters to obtain knowledge – diagrams apparently have cognitive surplus: they enable a quasi-intuitive form of knowledge. The present paper analyses the issue of diagrams’ cognitive value by enquiring into the tradition of symbolic cognition developed by Leibniz, Lambert, and Kant. The proposal resulting from this enquiry is to question the idea that the cognitive value of diagrams lies solely in allowing evidence for inferences. The imaginative dimension of diagrams connects reasoning to doxastic attitudes of meditation and enquiry. [ABSTRACT FROM AUTHOR]

This paper advances a version of the theory whereby logic had deep origins in democracy, by re-reading Gorgias' Encomium of Helen. Democracy, 'the government by debate', called political (and scientific) attention to the inferential abilities of citizens and to politicians' ability of taking advantage of them. Sophists, in particular, discovered that people's inferences follow constant repeatable forms, that these forms have impact on choices and decisions concerning public good, and then by dominating them you dominate politics in democracy. With the Encomium Gorgias launched these ideas, so laying the ground for Aristotle's science of deduction. [ABSTRACT FROM AUTHOR]

The Yogācāra school of logic developed a theory of sign-inferences that has many features of the Stoic and Epicurean logical teachings with small inclusions of Aristotelian ideas. In the Nyāyabindu of Dharmakīrti, we can find the following schemes of formal reasoning: modus Barbara (Figure I) and modus Camenes (Figure IV) of the Aristotelian syllogistic, and all the inference rules of the Stoic logic: modus ponens, modus tollens, modus ponendo tollens, modus tollendo ponens I, modus tollendo ponens II. The three premises of Yogācāra inference (if p, then q; there is an example that p and q occur together; p; then q) corresponds to the Epicurean doctrine of three premises with a necessary exemplification. Thus, the paper is a comparative study of Greek and Buddhist theory of sign-inferences, showing a deep similarity between them. [ABSTRACT FROM AUTHOR]

One of the main controversies of the Logic Schools of the 12th century centered on the question: What follows from the impossible? In this paper arguments for two diametrically opposed positions are examined. The author of the 'Avranches Text' who probably belonged to the school of the Parvipontani defended the view that from an impossible proposition everything follows ('Ex impossibili quodlibet'). In particular he developed a proof to show that by means of so-called 'disjunctive syllogism' any arbitrary proposition B can be logically derived from a pair of contradictory propositions A and Not-A. The author of the Ars Meliduna instead argued that nothing follows from an impossible proposition ('ex falso nihil sequitur'). This view is supported by various counterexamples which aimed to show that the admission of impossible premises would give rise to inconsistent conclusions. Upon closer analysis these inconsistencies do not, however, have the formal structure of a real contradiction like A and Not-A, but rather the structure of two rivalling conditionals like 'If B then A' and 'If B then Not-A'. Hence these counterexamples rather have to be considered as refutations of the basic principles of 'connexive logic'. [ABSTRACT FROM AUTHOR]

A number of medieval Arabic logicians discussed inferences that combine the principles of propositional and term logic, for example: Whenever H is Z then Every J is D No D is A Whenever H is Z then Some J is not A The present paper will be devoted to discussions of the validity of mixed conditional-categorical syllogisms of this form, and purported counterexamples, from Avicenna (d. 1037) to Urmawī (d. 1283). One major problem that was discussed, related to modern discussions of the context-sensitivity of counterfactual conditionals, is that if the antecedent of the conditional premise is incompatible with the categorical premise, then there is no guarantee that the latter will combine syllogistically with the consequent of the conditional premise. Plausible formalizations of the argument reinforce the misgivings expressed by some thirteenth-century Arabic logicians. [ABSTRACT FROM AUTHOR]

Richard Kimberly Heck and Paolo Mancosu have claimed that the possibility of non-Cantorian assignments of cardinalities to infinite concepts shows that Hume's Principle (HP) is not implicit in the concept of cardinal number. Neologicism would therefore be threatened by the 'good company' HP is kept by such alternative assignments. In his review of Mancosu's book, Bob Hale argues, however, that 'getting different numerosities for different countable infinite collections depends on taking the groups in a certain order – but it is of the essence of cardinal numbers that the cardinal size of a collection does not depend upon how its members are ordered'. This paper's goal is to implement Hale's response to the Good Company problem by producing a Cantorian argument for HP. In Section 2, we present the Heck-Mancosu argument against neologicism. In Section 3, we discuss Hale's defence of Hume's Principle. In Section 4, we discuss Cantor's abstractionist definitions of number. In Section 5, we argue that good abstraction must comply with what we call 'Gödel's Minimal Account of Abstraction' (GMAA). We finally show (Sections 5 and 6) that non-Cantorian theories of cardinality fail to satisfy GMAA. [ABSTRACT FROM AUTHOR]

Bernard Bolzano offers a criterion of individuation for ideas, according to which ideas are distinct if and only if they represent different objects or are composed differently. It fails to individuate ideas that are both simple and fail to represent, in particular syncategorematic ideas and logical constants. However, Bolzano also provides the means to close this gap. He suggests that we can distinguish ideas if they are not substitutable for each other in propositions, which we can, in turn, distinguish in terms of their truth-values. This paper explicates this suggestion and develops it into an improved individuation criterion for ideas: ideas also are distinct if we cannot replace them for one another in propositions salva veritate. [ABSTRACT FROM AUTHOR]

In this paper, the connection between logicism and the principle of tolerance in Carnap's philosophy of logic and mathematics is to be presented in terms of the history of its development. Such development is conditioned by two lines of criticism to Carnap's attempt to combine Logicism and Conventionalism, the first of which comes from Gödel, the second from Alfred Tarski. The presentation will take place in three steps. First, the Logicism of Carnap before the publication of The Logical Syntax of Language will be analyzed in its main features. Second, the relationship between Logicism and the Principle of Tolerance at the time of the publication of Logical Syntax, and thirdly, in the so-called semantical phase of Carnap's thought will be examined. On the basis of the two preceding points, we will then critically analyze two interpretations of the possibility to maintain a philosophical position like that of Carnap nowadays. [ABSTRACT FROM AUTHOR]