[…] their mistake is not that they are only form, but that form is missing. (Hegel 1986, 239)1. As far as the ‘association of friends’ edition1 can be believed, Hegel makes this judgment about the...

In 1995 Slater argued both against Priest’s paraconsistent system LP (1979) and against paraconsistency in general, invoking the fundamental opposition relations ruling the classical logical square. Around 2002 Béziau constructed a double defence of paraconsistency (logical and philosophical), relying, in its philosophical part, on Sesmat’s (1951) and Blanche’s (1953) “logical hexagon”, a geometrical, conservative extension of the logical square, and proposing a new (tridimensional) “solid of opposition”, meant to shed new light on the point raised by Slater. By using (...) n-opposition theory (NOT) we analyse Beziau’s anti-Slater move and show both its right intuitions and its technical limits. Moreover, we suggest that Slater’s criticism is much akin to a well-known one by Suszko (1975) against the conceivability of many-valued logics. This last criticism has been addressed by Malinowski (1990) and Shramko and Wansing (2005), who developed a family of tenable logical counter-examples to it: trans-Suszkian systems are radically many-valued. This family of new logics has some strange logical features, essentially: each system has more than one consequence operator. We show that a new, deeper part of the aforementioned geometry of logical oppositions (NOT), the “logical poly-simplexes of dimension m”, generates new logical-geometrical structures, essentially many-valued, which could be a very natural (and intuitive) geometrical counterpart to the “strange”, new, non-Suszkian logics of Malinowski, Shramko and Wansing. By a similar move, the geometry of opposition therefore sheds light both on the foundations of paraconsistent logics and on those of many-valued logics. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Philosophy and Rhetoric 36.2 (2003) 168-172 [Access article in PDF] Logic and the Art of Memory: The Quest for a Universal Language. Paolo Rossi. Trans. Stephen Clucas. Chicago: University of Chicago Press, 2000. Pp. xxviii + 333. $32.00 cloth. Of the traditional five canons of rhetoric—inventio, dispositio, elocutio, memoria, and actio—the most circuitous and fascinating history belongs to memoria. From its propulsion of Homeric lore to its (...) grounding of rhetorical invention to its exile under print culture to its recent revival in public memory studies, the promiscuous and perplexing history of memory in the West may be one of the least appreciated, and perhaps least understood, elements of rhetorical and intellectual history. The publication in 1966 of Frances Yates's highly praised The Art of Memory drew the attention of contemporary scholars to the importance of mnemotechnics to the culture of late medieval and early modern Europe. 1 Yates persuasively argued that the art of memory is an integral element of European intellectual history, one that can enrich our understanding of everything from Dominican theology to Shakespearian theater. However, six years earlier, in 1960, the Italian intellectual historian Paolo Rossi published in Italian an important precursor to Yates's work entitled Clavis Universalis: Arti Della Memoria e Logica Combinatoria da Lullo a Leibniz. The book traces the encyclopaedic and mnemotechnical traditions from Aristotle through Cicero and Raymond Lull and into the early-modern period, arguing that the art of memory provides an important antecedent to the advent of method in seventeenth-century philosophy, especially in the works of Bacon, Descartes, and Leibniz. Yates, in her preface to The Art of Memory, acknowledges her debt to Rossi's work, and now this work has been made available in English translation. Stephen Clucas's translation, under the title Logic and the Art of Memory, will no doubt stimulate and supplement research into the mnemotechnical tradition in the English-speaking world, and perhaps lead us to reconsider the relationship between philosophy and rhetoric.Rossi argues that the neglect of the mnemotechnical tradition in its Ciceronian and Lullian strands has distorted our understanding of the "new" science and philosophy of the seventeenth-century, which is often interpreted as constituting, in a Kuhnian sense, a drastic paradigm shift from a [End Page 168] Renaissance worldview that still retained occult elements. Rossi places the work of Bacon, Descartes, and Leibniz within the historical strand of the logico-encyclopaedic and mnemotechnical traditions, suggesting that these figures culminate late medieval and early modern intellectual and cultural ambitions as much as they give rise to new ones. Rossi makes his argument by providing a history of mnemotechnics from Aristotle into the fifteenth century in chapter one; by examining the fascination with encyclopaedism, combinatoria, and memory in the sixteenth century in chapters two and three; by investigating the role of artificial memory in the works of key intellectual figures in the late sixteenth and seventeenth centuries in chapters four through six; and by tracing the impulse toward universal knowledge and its connection to mnemotechnics among seventeenth-century Cartesians, Baconians, and in the work of Leibniz, in chapters seven and eight.Chapter one, after showing the pervasiveness of Renaissance mnemotechnical literature, surveys its classical and medieval antecedents in philosophy and rhetoric. Rossi argues that Aristotle's De memoria et reminiscentia, Cicero's De oratore, Quintilian's De institutione oratoria, the Rhetorica ad Herennium, and the works of Albertus Magnus and Thomas Aquinas were each important to the mnemotechnical tradition into the seventeenth century. Fourteenth- and fifteenth-century treatises on the ars memorativa and the ars predicandi, drawing on these classical and medieval theories, emphasize the importance of memory places (loci), images (imagines), and order or arrangement (dispositio) in mnemotechnics. Additionally, they intimately link the memory to the imagination, stressing the importance of exciting and stimulating the imagination in memorization. The Italian Pietro da Ravenna, for example, attributed the might of his memory to, in his own words, turning "the images of the most beautiful virgins into memory places" (22). Such imaginative mnemonic techniques were considered to... (shrink)

It is quite common to refer to al-Ghazālī as one of the most important thinkers in the Islamic intellectual tradition. Aladdin M. Yaqub’s Al-Ghazālī’s Moderation in Belief: al-Iqtiṣād fī al-i’tiqād shows that this remark is not hyperbolic. And this volume has many characteristics of a good translation of classical texts. First of all, Aladdin M. Yaqub is very consistent with his use of terminology. He explains his preferences for Arabic philosophical terms in “Note on the Translation”. As is well (...) known, Moderation in Belief is the first text in which classical Greek logic is systematically used in Islamic theology (see the “Fourth Introduction: On explaining the methods of proof that we employ in... (shrink)

This guide accompanies the following article: ‘Logic and Divine Simplicity’. Philosophy Compass 6/4 : pp. 282–294, doi: Author’s IntroductionFirst‐order formalizations of classical theistic doctrines are increasingly used in contemporary work in philosophy of religion and philosophical theology, as a means for clarifying the conceptual structure of the doctrines and their role in inferential procedures. But there are a variety of different ways in which such doctrines have been formalized, each representing the doctrines as having different conceptual structures. Moreover, (...) the adequacy of such formalizations as such has, at least with respect to some classes of doctrines, been disputed. One reason for disputing their adequacy derives from the conceptual impact of classical theism’s doctrine of divine simplicity.Author RecommendsFrege, Gottlob ‘Begriffsschrift: a formula language of pure thought,’ trans. Michael Beany, in The Frege Reader, ed. Beany. Oxford: Blackwell, pp. 47–78. The preface contains interesting remarks about the purpose of formalization as understood by the chief pioneer of modern formal logic. These remarks are also connected by Frege to his views on the relation between thought and language more generally.Russell, Bertrand, and Whitehead, A.N. Principia Mathematica, Vol. I. Cambridge: Cambridge University Press.The preface and first section of the long introduction contain remarks on the purpose and advantages of formalization. Chapter 1 of the introduction contains what is probably one of the first formalizations ever of a theistic doctrine, and is given in terms of a definite description analysis.Suppes, Patrick ‘The Desirability of Formalization in Science,’The Journal of Philosophy, Vol. 65, No. 20, pp. 651–64.Clear and concise discussion of some of the advantages of formalization in philosophical inquiry, written by a prominent contemporary American philosopher‐logician.Nieznański, Edward ‘The Beginnings of Formalization in Theology,’ in Advances in Scientific Philosophy: Essays in Honour of Paul Weingartner, eds. Gerhard Schurz and Gregory J.W. Dorn. Amsterdam and Atlanta, GA: Ropodi, pp. 551–9.A valuable paper that narrates, among other things, the programme of formalizing theistic doctrines that emerged in Poland in the 1920s under the influence of the Lvov‐Warsaw School. Various examples of formalizations are also given.Quine, W.V.O. Mathematical Logic. Cambridge, MA: Harvard University Press.In Section 27 of this classic study, Quine offers a formalization of theistic doctrines which seeks to avoid the difficulties of earlier formalizations by means of a subtle extensional singleton set analysis. The proposal has not won many adherents, but is worthy of careful study nonetheless.Woleński, Jan ‘Theism, Fideism, Atheism, Agnosticism,’ in Logic, Ethics and All That Jazz: Essays in Honour of Jordan Howard Sobel, eds. Lars‐Göran Johansson, Jan Österberg, and Rysiek Sliwinski. Uppsala: Uppsala Philosophical Studies, pp. 387–400.A concise but lucid survey of some attempts to formalize theistic doctrines and some problems besetting these attempts. Woleński also proposes his own method of formalization, which could be described as a simplified version of Quine’s method in Mathematical Logic.Bocheński, Joseph The Logic of Religion. New York: New York University Press.The first book‐length treatment of the relation between modern logic and theism. It covers much ground, and remains very readable.Alston, William P. ‘Religious Language and Verificationism,’ in The Rationality of Theism, eds. Paul Moser and Paul Copan. London: Routledge, pp. 17–34.Identifies some problems with attempts at articulating theistic doctrines by means of subject‐predicate language. Highly relevant to formalizations of theistic doctrines, even though this topic is not dealt with explicitly.Kraal, Anders ‘Logic and Divine Simplicity,’Philosophy Compass.Offers a survey of three main methods of formalizing theistic doctrines, and of some variants of these methods. Argues that certain formalizations of theistic doctrines are bound to be rejected as conceptually inadequate by all who understand the doctrines at hand within the framework provided by the traditional doctrine of divine simplicity.Sample Syllabus Week I: The Idea of Formalization and the Project of Formalizing Theistic Doctrines Reading:Frege, Gottlob ‘Begriffsschrift: a formula language of pure thought,’ trans. Michael Beany, in The Frege Reader, ed. Beany. Oxford: Blackwell, pp. 47–78. Russell, Bertrand, and Whitehead, A.N. Principia Mathematica, Vol. I. Cambridge: Cambridge University Press. Suppes, Patrick ‘The Desirability of Formalization in Science,’The Journal of Philosophy, Vol. 65, No. 20, pp. 651–64.Nieznański, Edward ‘The Beginnings of Formalization in Theology,’ in Advances in Scientific Philosophy: Essays in Honour of Paul Weingartner, eds. Gerhard Schurz and Gregory J.W. Dorn. Amsterdam and Atlanta, GA: Ropodi, pp. 551–9. Week II: Formalizing Theistic Doctrines: Three Alternative Methods Reading:Woleński, Jan ‘Theism, Fideism, Atheism, Agnosticism,’ in Logic, Ethics and All That Jazz: Essays in Honour of Jordan Howard Sobel, eds. Lars‐Göran Johansson, Jan Österberg, and Rysiek Sliwinski. Uppsala: Uppsala Philosophical Studies, pp. 387–400.Russell, Bertrand, and Whitehead, A.N. Principia Mathematica, Vol. I. Cambridge: Cambridge University Press. Quine, W.V.O. Mathematical Logic. Cambridge, MA: Harvard University Press. Week III: Arguments for and Against Some Formalizations of Theistic Doctrines Reading:Bocheński, Joseph The Logic of Religion. New York: New York University Press. Kraal, Anders ‘Logic and Divine Simplicity,’Philosophy Compass, Vol. 6, No. 4, pp. 282–94.Focus Questions1 What do Frege, Russell and Whitehead, and Suppes understand the purpose or purposes of logical formalization to be, and why do they think formalization can achieve these purposes?2 Woleński sketches some simple ways of formalizing theistic doctrines such as ‘God exists’ or ‘God is almighty’ in terms of 1‐place predicates which he subsequently abandons in favour of other methods. What reasons lead him to abandon these more simple methods of formalization?3 What are the advantages of the definite description formalization of theistic doctrines offered by Russell and Whitehead?4 Quine offers a subtle formalization of the theistic doctrine ‘God exists’ in terms of singleton sets. What problems are Quine’s formalization intended to accommodate, and how does it seek to accommodate them?5 Which relative merits or demerits are there in Bocheński’s and Kraal’s respective arguments for and against the adequacy of certain formalizations of theistic doctrines? (shrink)

This paper undertakes an intersectional reading of visual art through theories of literary interpretation in Sanskrit poetics in close reading with Deleuze's notions of sensation. The concept of Dhvani – the Indian theory of suggestion which can be translated as resonance, as explored in the Rasa – Dhvani aesthetics offers key insights into understanding the mode in which sensation as discussed by Deleuze operates throughout his reflections on Francis Bacon's and Cézanne's works. The paper constructs a comparative framework to review (...) modern and classical art history, mainly in the medium of painting, through an understanding of the concept of Dhvani, and charts a course of reinterpreting and examining possible points of concurrence and departure with respect to the Deleuzian logic of sensation and his notions of time-image and perception. The author thereby aims to move art interpretation's paradigm towards a non-linguistic sensory paradigm of experience. The focus of the paper is to break the moulds of normative theory-making which guide ideal conditions of ‘understanding art’ and look into alternative modes of experiencing the ‘vocabulary’ of art through trans-disciplinary intersections, in this case the disciplines being those of visual art, literature and phenomenology. (shrink)

The background to the development of proof theory since 1960 is contained in the article (MATHEMATICS, FOUNDATIONS OF), Vol. 5, pp. 208- 209. Brie y, Hilbert's program (H.P.), inaugurated in the 1920s, aimed to secure the foundations of mathematics by giving nitary consistency proofs of formal systems such as for number theory, analysis and set theory, in which informal mathematics can be represented directly. These systems are based on classical logic and implicitly or explicitly depend on the assumption (...) of \completed in nite" totalities. Consistency of a system S (containing a modicum of elementary number theory) is su cient to ensure that any nitary meaningful statement about the natural numbers which is provable in S is correct under the intended interpretation. Thus, in Hilbert's view, consistency of S would serve to eliminate the \completed in nite" in favor of the \potential in nite" and thus secure the body of mathematics represented in S. Hilbert established the subject of proof theory as a technical part of mathematical logic by means of which his program was to be carried out its methods will be described below. In 1931, Godel's second incompleteness theorem raised a prima facieobstacle to H.P. for the system Z of elementary number theory (also called Peano Arithmetic, and denoted below by PA) since all previously recognized forms of nitary reasoning could be formalized within it. In any case, Hilbert's program could not possibly succeed for any system such as set theory in which all nitary notions and reasoning could unquestionably be formalized. These obstacles led workers in proof theory to modify H.P. in two kinds of ways. The rst was to seek reductions of various formal systems S to more constructive systems S 0. The second was to shift the aims from foundational ones to more mathematical ones. Examples of 1 the former move are the reductions of PA to intuitionistic arithmetic HA, and Gentzen's consistency proof of PA by nitary reasoning coupled with quanti er-free trans nite induction up to the ordinal , TI( 0), both obtained in the 1930s (cf.. (shrink)

In a time in which an exuberant, trans-classical, non-trivial machine culture redesigns terminologies, remodels logics, produces new evidence, and reorganizes semantic resources, a new, neocybernetic regime of truth is taking shape. Many of our recent self-descriptions and theory formations are coined by our media-technological condition. Nowhere is this more apparent than in the work of Niklas Luhmann, especially in his inherent narrative of the history of rationality. This essay attempts to reconstruct Luhmann’s redescription of European rationality, especially the (...) media- and machine-historical conditions that remain apparent in Luhmann’s account. The decisive issue is that Luhmann’s history of rationality reveals the technological unconscious of systems theory and indeed the epochal imaginary it belongs to. With the help of the theories of machines developed by von Foerster, Simondon and Günther, Luhmann’s oeuvre must be read as probably the most striking conceptual edifice to emerge from what could be called the 20th-century’s epochal technological shift of meaning. (shrink)

In [U. Kohlenbach, Some logical metatheorems with applications in functional analysis, Trans. Amer. Math. Soc. 357 89–128], the second author obtained metatheorems for the extraction of effective bounds from classical, prima facie non-constructive proofs in functional analysis. These metatheorems for the first time cover general classes of structures like arbitrary metric, hyperbolic, CAT and normed linear spaces and guarantee the independence of the bounds from parameters ranging over metrically bounded spaces. Recently ]), the authors obtained generalizations of these (...) metatheorems which allow one to prove similar uniformities even for unbounded spaces as long as certain local boundedness conditions are satisfied. The use of classical logic imposes some severe restrictions on the formulas and proofs for which the extraction can be carried out. In this paper we consider similar metatheorems for semi-intuitionistic proofs, i.e. proofs in an intuitionistic setting enriched with certain non-constructive principles. Contrary to the classical case, there are practically no restrictions on the logical complexity of theorems for which bounds can be extracted. Again, our metatheorems guarantee very general uniformities, even in cases where the existence of uniform bounds is not obtainable by straightforward functional analytic means. Already in the purely intuitionistic case, where the existence of effective bounds is implicit, the metatheorems allow one to derive uniformities that may not be obvious at all from a given constructive proof. Finally, we illustrate our main metatheorem by an example from metric fixed point theory. (shrink)

This revised and considerably expanded 2nd edition brings together a wide range of topics, including modal, tense, conditional, intuitionist, many-valued, paraconsistent, relevant, and fuzzy logics. Part 1, on propositional logic, is the old Introduction, but contains much new material. Part 2 is entirely new, and covers quantification and identity for all the logics in Part 1. The material is unified by the underlying theme of world semantics. All of the topics are explained clearly using devices such as tableau proofs, (...) and their relation to current philosophical issues and debates are discussed. Students with a basic understanding of classical logic will find this book an invaluable introduction to an area that has become of central importance in both logic and philosophy. It will also interest people working in mathematics and computer science who wish to know about the area. (shrink)

Semantic justifications of the classical rules of logical inference typically make use of a notion of bivalent truth, understood as a property guaranteed to attach to a sentence or its negation regardless of the prospects for speakers to determine it as so doing. For want of a convincing alternative account of classical logic, some philosophers suspicious of such recognition-transcending bivalence have seen no choice but to declare classical deduction unwarranted and settle for a weaker system; intuitionistic (...) logic in particular, buttressed by assertion-conditional semantics, is often considered to enjoy a degree of meaning-theoretical respectability unattainable by classical logic.The decision to forgo the classical inference rules is not always made lightly. Thus, Dummett: " In the resolution of the conflict between [the view that generally accepted classical modes of inference ought to be theoretically accommodated, and the demand that any such accommodation be achieved without recourse to bivalence] lies, as I see it, one of the most fundamental and intractable problems in the theory of meaning; indeed, in all philosophy. "The present article ventures to suggest that the conflict need not be irresoluble. Helping ourselves only to such conceptual resources as are standardly invoked by proponents of intuitionistic logic, we shall formulate a rudimentary meaning theory for a selection of logical constants, define a relation of valid inferability, and prove that the latter includes all of classical first-order logic. The result is essentially that reported in Sandqvist as Theorem 2.20.2. TheoryWe will be considering a standard-syntax first-order language with ⊃, ⊥ and ∀ as its only primitive logical constants. We assume countable supplies of individual constants, individual functors , and predicates , as well as a denumerably infinite set of individual variables. By a basic 1 formula we will mean one that …[Full Text of this Article]. (shrink)

An old and well-known objection to non-classical logics is that they are too weak; in particular, they cannot prove a number of important mathematical results. A promising strategy to deal with this objection consists in proving so-called recapture results. Roughly, these results show that classical logic can be used in mathematics and other unproblematic contexts. However, the strategy faces some potential problems. First, typical recapture results are formulated in a purely logical language, and do not generalize nicely (...) to languages containing the kind of vocabulary that usually motivates non-classical theories—for example, a language containing a naïve truth predicate. Second, proofs of recapture results typically employ classical principles that are not valid in the targeted non-classical system; hence, non-classical theorists do not seem entitled to those results. In this paper, we analyze these problems and provide solutions on behalf of non-classical theorists. To address the first problem, we provide a novel kind of recapture result, which generalizes nicely to a truth-theoretic language. As for the second problem, we argue that it relies on an ambiguity and that, once the ambiguity is removed, there are no reasons to think that non-classical logicians are not entitled to their recapture results. (shrink)

The essay reconstructs Gotthard Günther’s interpretation of Fichte’s philosophy. The starting point of this reconstruction are Günther’s investigations into a formal logic of reflection and their approaches in German idealism. Particular attention is given to the volitional aspect of Günther’s logic. According to Günther, Fichte is the first philosopher clearly to see and to explain the duality of reflection posed by Kant as a problem. According to Günther, the second important contribution of Fichte is the insight that thinking (...) in the double reflection is no longer a passive reflection but an action. Despite these two starting points, Fichte does not transcend the framework of classical thought. This is because of his identification of thinking and acting or willing. Their separation is finally accomplished only in Schelling’s late philosophy, in which a change of theme from being to action takes place. This allows the separation of form and content in the double reflection as well. Günther’s introduction of the will into logic is based on the distinction between logical value and ontological location. The latter is, as a floating exchange relation, an indeterminate vacancy which can be occupied by logical values. This assignment is accomplished, which represents Günther’s transference of the Fichtean theory of positing to the theory of trans-classical technique, no longer by thinking, but by way of technical construction.Der Aufsatz rekonstruiert Gotthard Günthers Interpretation der Philosophie Fichtes. Ausgangspunkt dieser Rekonstruktion sind Günthers Untersuchungen zu einer formalen Logik der Reflexion und deren Ansätzen im deutschen Idealismus. Ein besonderes Augenmerk gilt dabei dem volitiven Aspekt von Günthers Logik.Günther zufolge ist Fichte der erste Philosoph, der die von Kant als Problem aufgeworfene Doppelstufigkeit der Reflexion klar gesehen und expliziert hat. Der zweite bedeutsame Beitrag Fichtes besteht nach Günther in der Einsicht, dass in der doppelten Reflexion das Denken nicht mehr passive Widerspiegelung, sondern Handlung ist.Trotz dieser beiden Ansatzpunkte verlässt Fichte den Rahmen des klassischen Denkens aufgrund seiner Identifizierung von Denken und Handeln bzw. Wollen nicht. Deren Trennung wird erst in Schellings Spätphilosophie vorgenommen, in der sich ein Themawechsel vom Sein zur Handlung vollzieht. Dies ermöglicht die Trennung von Form und Inhalt auch in der doppelten Reflexion.Günthers Introduktion des Willens in die Logik erfolgt anhand der Unterscheidung von logischem Wert und ontologischem Ort. Letzterer ist als schwebendes Umtauschverhältnis eine unbestimmte Leerstelle, die durch logische Werte besetzt werden kann. Diese Wertbesetzung erfolgt, und das ist Günthers Übertragung der Fichteschen Theorie des Setzens auf die Theorie trans-klassischer Technik, nicht mehr durch das Denken, sondern auf dem Wege technischer Konstruktion. (shrink)

This interesting collection is the Festschrift presented to W. Britzelmayr on his seventieth birthday, and it contains several excellent papers which ought to interest the logician and philosophical analyst alike. The most exciting paper is one by Stegmüller in which a system of set theory combining ideas from Bernays and Quine is formulated; one by Kurt Schütte discusses the limitations imposed by constructive logic on the theory of trans finite arithmetic; there are papers by each of the editors: (...) the first analyzes the deduction theorem for the first order predicate calculus, while the second treats logics with predicate quantifiers. Other papers include studies by Behmann on the philosophico-logical status of identity; by Beth on the application of his semantic tableaux to classical logic; by Wilhelmy on the semantics of quantified, many-valued logics; and by E. M. Fels concerning the work of Markov and his school in the theory of canonical systems. There are still further papers which take as their topics the logical analysis of legal concepts and reasoning, the logic of questions, the semantics of implication in ordinary language, and the relation of the theory of logical types to Frege's work. In general, this is an excellent collection which affords a wide view of the logico-linguistic concerns of recent German philosophy.—P. J. M. (shrink)

Connexive logics are based on two ideas: that no statement entails or is entailed by its own negation (this is Aristotle’s thesis) and that no statement entails both something and the negation of this very thing (this is Boethius' thesis). Usually, connexive logics are contra-classical. In this note, I introduce a reading of the connexive theses that makes them compatible with classical logic. According to this reading, the theses in question do not talk about validity alone; rather, (...) they talk in part about (a property related to) the soundness of arguments. (shrink)

In Sect. 1 it is argued that systems of logic are exceptional, but not a priori necessary. Logics are exceptional because they can neither be demonstrated as valid nor be confirmed by observation without entering a circle, and their motivation based on intuition is unreliable. On the other hand, logics do not express a priori necessities of thinking because alternative non-classical logics have been developed. Section 2 reflects the controversies about four major kinds of non-classical logics—multi-valued, intuitionistic, (...) paraconsistent and quantum logics. Its purpose is to show that there is no particular domain or reason that demands the use of a non-classical logic; the particular reasons given for the non-classical logic can also be handled within classical logic. The result of Sect. 2 is substantiated in Sect. 3, where it is shown (referring to other work) that all four kinds of non-classical logics can be translated into classical logic in a meaning-preserving way. Based on this fact a justification of classical logic is developed in Sect. 4 that is based on its representational optimality. It is pointed out that not many but a few non-classical logics can be likewise representationally optimal. However, the situation is not symmetric: classical logic has ceteris paribus advantages as a unifying metalogic, while non-classical logics can have local simplicity advantages. (shrink)

We give a proof-theoretic as well as a semantic characterization of a logic in the signature with conjunction, disjunction, negation, and the universal and existential quantifiers that we suggest has a certain fundamental status. We present a Fitch-style natural deduction system for the logic that contains only the introduction and elimination rules for the logical constants. From this starting point, if one adds the rule that Fitch called Reiteration, one obtains a proof system for intuitionistic logic in (...) the given signature; if instead of adding Reiteration, one adds the rule of Reductio ad Absurdum, one obtains a proof system for orthologic; by adding both Reiteration and Reductio, one obtains a proof system for classical logic. Arguably neither Reiteration nor Reductio is as intimately related to the meaning of the connectives as the introduction and elimination rules are, so the base logic we identify serves as a more fundamental starting point and common ground between proponents of intuitionistic logic, orthologic, and classical logic. The algebraic semantics for the logic we motivate proof-theoretically is based on bounded lattices equipped with what has been called a weak pseudocomplementation. We show that such lattice expansions are representable using a set together with a reflexive binary relation satisfying a simple first-order condition, which yields an elegant relational semantics for the logic. This builds on our previous study of representations of lattices with negations, which we extend and specialize for several types of negation in addition to weak pseudocomplementation; in an appendix, we further extend this representation to lattices with implications. Finally, we discuss adding to our logic a conditional obeying only introduction and elimination rules, interpreted as a modality using a family of accessibility relations. (shrink)

In their recent article “A Hierarchy of Classical and Paraconsistent Logics”, Eduardo Barrio, Federico Pailos and Damien Szmuc present novel and striking results about meta-inferential validity in various three valued logics. In the process, they have thrown open the door to a hitherto unrecognized domain of non-classical logics with surprising intrinsic properties, as well as subtle and interesting relations to various familiar logics, including classical logic. One such result is that, for each natural number n, there (...) is a logic which agrees with classical logic on tautologies, inferences, meta-inferences, meta-meta-inferences, meta-meta-...-meta-inferences, but that disagrees with classical logic on n + 1-meta-inferences. They suggest that this shows that classical logic can only be characterized by defining its valid inferences at all orders. In this article, I invoke some simple symmetric generalizations of BPS’s results to show that the problem is worse than they suggest, since in fact there are logics that agree with classical logic on inferential validity to all orders but still intuitively differ from it. I then discuss the relevance of these results for truth theory and the classification problem. (shrink)

We offer a critical overview of two sorts of proof systems that may be said to characterize classical propositional logic indirectly (and non-standardly): refutation systems, which prove sound and complete with respect to classical contradictions, and rejection systems, which prove sound and complete with respect to the larger set of all classical non-tautologies. Systems of the latter sort are especially interesting, as they show that classical propositional logic can be given a paraconsistent characterization. In (...) both cases, we consider Hilbert-style systems as well as Gentzen-style sequent calculi and natural-deduction formalisms. (shrink)

Reasoning with conditionals is often thought to be non-monotonic, but there is no incompatibility with classical logic, and no need to formalise inference itself as probabilistic. When the addition of a new premise leads to abandonment of a previously compelling conclusion reached by modus ponens, for example, this is generally because it is hard to think of a model in which the conditional and the new premise are true.

Classical logic is often characterized through certain laws such as bi-valence and sharpness of concepts, among others. My view is that its most fundamental feature is a commitment to an objective conception of truth, which goes together with a realistic metaphysical view. Truth is objective in that it derives from the nature of reality, and is not dependent on beliefs, theories, practices, and the like. Classical logic is a theory of logical properties, logical truths, and logical (...) states of affairs. (shrink)

Western (deductive) logic originated in Greek antiquity. It found its first expression in those works of the great philosopher Aristotle (384–322 BC) which have come to be known as the Organon, i.e., ‘instrument’. Aristotle’s logic, also known as syllogistics, was unsystematically concerned with patterns of reasoning and argumentation. It remained in this rudimentary state relatively unchanged and unchallenged until the second half of the nineteenth century. At that time, logic underwent a period of unprecedented reform and modernization, (...) due in large part to the German mathematician Gottlob Frege (1848– 1925) It thus became more and more a mathematical endeavor of studying the structure and peculiarities of artificial, formal languages. In this new form, logic gave rise in the twentieth century to disciplines such as theoretical informatics and programming languages, and transformed our lives through computation, information processing, and the Internet. A formal language consists, in effect, of a particular alphabet and some precise rules of forming, and transforming, strings over this alphabet. There exist several types of formal languages analyzed in logic. Depending on their structure, they are called first-order languages, second-order languages, and so on. Today a logic is considered a theory of such a language and is, correspondingly, referred to as a first-order logic, a second-order logic, and so on. In this chapter, we shall outline a first-order logic as a paragon of deductive logic. Its full name is: “Classical, first-order predicate logic with identity”. What all these expressions mean exactly, will become clear below. The logic we shall study first is termed classical logic because the idea to create such an instrument, or ‘organon’, is rooted in Greek antiquity. Owing to its origin, it is based on three time-honored Aristotelian doctrines. For these and several other reasons that we shall discuss later in this chapter, it is also called a logic of the Aristotelian style, or an Aristotelian logic for short. (shrink)

The subject of Labelled Non-Classical Logics is the development and investigation of a framework for the modular and uniform presentation and implementation of non-classical logics, in particular modal and relevance logics. Logics are presented as labelled deduction systems, which are proved to be sound and complete with respect to the corresponding Kripke-style semantics. We investigate the proof theory of our systems, and show them to possess structural properties such as normalization and the subformula property, which we exploit not (...) only to establish advantages and limitations of our approach with respect to related ones, but also to give, by means of a substructural analysis, a new proof-theoretic method for investigating decidability and complexity of (some of) the logics we consider. All of our deduction systems have been implemented in the generic theorem prover Isabelle, thus providing a simple and natural environment for interactive proof development. Labelled Non-Classical Logics is essential reading for researchers and practitioners interested in the theory and applications of non-classical logics. (shrink)

An account of the logic of bivalent languages with truth-value gaps is given. This account is keyed to the use of tables introduced by S. C. Kleene. The account has two guiding ideas. First, that the bivalence property insures that the language satisfies classical logic. Second, that the general concepts of a valid sentence and an inconsistent sentence are, respectively, as sentences which are not false in any model and sentences which are not true in any model. (...) What recommends this approach is (1) its relative simplicity, and (2) the fact that it leaves the fundamental features of classical logic intact. (shrink)

This paper provides a defense of the full strength of classical logic, in a certain form, against those who would appeal to semantic paradox or vagueness in an argument for a weaker logic. I will not argue that these paradoxes are based on mistaken principles; the approach I recommend will extend a familiar formulation of classical logic by including a fully transparent truth predicate and fully tolerant vague predicates. It has been claimed that these principles (...) are not compatible with classical logic; I will argue, by both drawing on previous work and presenting new work in the same vein, that this is not so. We can combine classical logic with these intuitive principles, so long as we allow the result to be nontransitive. In the end, I hope the paper will help us to handle familiar paradoxes within classical logic; along the way, I hope to shed some light on what classical logic might be for. (shrink)

In this paper, we make distinctions between Classical Logic (where the propositions are 100% true, or 100 false) and the Neutrosophic Logic (where one deals with partially true, partially indeterminate and partially false propositions) in order to respond to K. Georgiev’s criticism [1]. We recall that if an axiom is true in a classical logic system, it is not necessarily that the axiom be valid in a modern (fuzzy, intuitionistic fuzzy, neutrosophic etc.) logic system.

Recently, it has been proposed to understand a logic as containing not only a validity canon for inferences but also a validity canon for metainferences of any finite level. Then, it has been shown that it is possible to construct infinite hierarchies of "increasingly classical" logics—that is, logics that are classical at the level of inferences and of increasingly higher metainferences—all of which admit a transparent truth predicate. In this paper, we extend this line of investigation by (...) taking a somehow different route. We explore logics that are different from classical logic at the level of inferences, but recover some important aspects of classical logic at every metainferential level. We dub such systems meta-classical non-classical logics. We argue that the systems presented deserve to be regarded as logics in their own right and, moreover, are potentially useful for the non-classical logician. (shrink)

In distinction from the well-known double-negation embeddings of the classical logic we consider some variants of single-negation embeddings and describe some classes of superintuitionistic first-order predicate logics in which the classical first-order calculus is interpretable in such a way. Also we find the minimal extensions of Heyting's logic in which the classical predicate logic can be embedded by means of these translations.

Typically, a logic consists of a formal or informal language together with a deductive system and/or a model-theoretic semantics. The language is, or corresponds to, a part of a natural language like English or Greek. The deductive system is to capture, codify, or simply record which inferences are correct for the given language, and the semantics is to capture, codify, or record the meanings, or truth-conditions, or possible truth conditions, for at least part of the language.

A simple method is provided for translating proofs in Grentzen's LK into proofs in Gentzen's LJ with the Peirce rule adjoined. A consequence is a simpler cut elimination operator for LJ + Peirce that is primitive recursive.

Only propositional logics are at issue here. Such a logic is contra-classical in a superficial sense if it is not a sublogic of classical logic, and in a deeper sense, if there is no way of translating its connectives, the result of which translation gives a sublogic of classical logic. After some motivating examples, we investigate the incidence of contra-classicality (in the deeper sense) in various logical frameworks. In Sections 3 and 4 we will (...) encounter, originally as an example of what (in Section 2) we call a contra-classical modal logic, an unusual logic boasting a connective (" demi-negation" ) whose double application is equivalent to a single application of the negation connective. Pondering the example points the way to a general characterization of contra-classicality (Theorems 3.3 and 4.6). In an Appendix (Section 5), we look at one alternative to classical logic as the target for such translational assimilation, intuitionistic logic, calling logics which resist the assimilation, in this case, contra- intuitionistic. We will show that one such logic is classical logic itself, thereby strengthening a result of Wojcicki's to the effect that the consequence relation of classical logic cannot be faithfully embedded by any connective-by-connective translation into that of intuitionistic logic. (What the "faithfully" means here is that not only is the translation of anything provable in the 'source' logic.. (shrink)

In the present paper we give the first proof-theoretical example of an embedding of classical logic into a quantum-like logic. This is performed in the framework of basic logic, where a proof-theoretical approach to quantum logic is convenient. We consider basic orthologic, that corresponds to a sequential formulation of paraconsistent quantum logic, and which is given by basic orthologic added with weakening and contraction, in a language with Girard's negation. In the paper we first (...) consider a convenient cut-free calculus for classical logic, in the same language; then, in a language enriched with a new kind of literals, we introduce basic orthologic with a primitive modality, where classical logic is embeddable. Similarly to Girard's negation, our modality is not a connective but conceivable as an operator defined inductively on the set of formulae. This allows us to obtain a calculus which enjoys cut-elimination. (shrink)

This is the first introductory textbook on non-classical propositional logics.

Bilateralists hold that the meanings of the connectives are determined by rules of inference for their use in deductive reasoning with asserted and denied formulas. This paper presents two bilateral connectives comparable to Prior's tonk, for which, unlike for tonk, there are reduction steps for the removal of maximal formulas arising from introducing and eliminating formulas with those connectives as main operators. Adding either of them to bilateral classical logic results in an incoherent system. One way around this (...) problem is to count formulas as maximal that are the conclusion of reductio and major premise of an elimination rule and to require their removability from deductions. The main part of the paper consists in a proof of a normalisation theorem for bilateral logic. The closing sections address philosophical concerns whether the proof provides a satisfactory solution to the problem at hand and confronts bilateralists with the dilemma that a bilateral notion of stability sits uneasily with the core bilateral thesis. (shrink)

We consider structures of the form (Z;+,C), where C is an additive cyclic order on (Z;+). We show that such structures are dp-minimal and in this way produce a continuum-size family of dp-minimal expansions of (Z;+) such that no two members of the family define the same subsets of Z.

We examine the set of formula-to-formula valid inferences of Classical Logic, where the premise and the conclusion share at least a propositional variable in common. We review the fact, already proved in the literature, that such a system is identical to the first-degree entailment fragment of R. Epstein's Relatedness Logic, and that it is a non-transitive logic of the sort investigated by S. Frankowski and others. Furthermore, we provide a semantics and a calculus for this (...) class='Hi'>logic. The semantics is defined in terms of a \-matrix built on top of a 5-valued extension of the 3-element weak Kleene algebra, whereas the calculus is defined in terms of a Gentzen-style sequent system where the left and right negation rules are subject to linguistic constraints. (shrink)

One of the most fruitful applications of substructural logics stems from their capacity to deal with self-referential paradoxes, especially truth-theoretic paradoxes. Both the structural rules of contraction and the rule of cut play a crucial role in typical paradoxical arguments. In this paper I address a number of difficulties affecting noncontractive approaches to paradox that have been discussed in the recent literature. The situation was roughly this: if you decide to go substructural, the nontransitive approach to truth offers a lot (...) of benefits that are not available in the noncontractive account. I sketch a noncontractive theory of truth that has these benefits. In particular, it has both a proof- and a model-theoretic presentation, it can be extended to a first-order language, and it retains every classically valid inference. (shrink)

Recently, Coquand and Palmgren considered systems of intuitionistic arithmetic in a finite types together with various forms of the axiom of choice and a numerical omniscience schema which implies classical logic for arithmetical formulas. Feferman subsequently observed that the proof theoretic strength of such systems can be determined by functional interpretation based on a non-constructive μ-operator and his well-known results on the strength of this operator from the 70's. In this note we consider a weaker form LNOS of (...) NOS which suffices to derive the strong form of binary König's lemma studied by Coquand/Palmgren and gives rise to a new and mathematically strong semi-classical system which, nevertheless, can proof theoretically be reduced to primitive recursive arithmetic PRA. The proof of this fact relies on functional interpretation and a majorization technique developed in a previous paper. (shrink)

The purpose of this paper is to provide a new system of logic for existence and essence, in which the traditional distinctions between essential and accidental properties, abstract and concrete objects, and actually existent and possibly existent objects are described and related in a suitable way. In order to accomplish this task, a primitive relation of essential identity between different objects is introduced and connected to a first order existence property and a first order abstractness property. The basic idea (...) is that possibly existent objects are completely determinate and that essentially identical objects are just different individuations of the same individual essence. Accordingly, essential properties are defined as properties that are invariant with respect to this kind of identity, while abstract objects are determined by being characterized by essential properties only. Once such ideas are implemented, a number of classical intuitions about objects, their essence, and their way of existence can be consistently interpreted. (shrink)

I show that it is not possible to uniquely characterize classical logic when working within classical set theory. By building on recent work by Eduardo Barrio, Federico Pailos, and Damian Szmuc, I show that for every inferential level (finite and transfinite), either classical logic is not unique at that level or there exist intuitively valid inferences of that level that are not definable in modern classical set theory. The classical logician is thereby faced (...) with a three-horned dilemma: Give up uniqueness but preserve characterizability, give up characterizability and preserve uniqueness, or (potentially) preserve both but give up modern classical set theory. After proving the main result, I briefly explore this third option by developing an account of classical logic within a paraconsistent set theory. This account of classical logic ensures unique characterizability in some sense, but the non-classical set theory also produces highly non-classical meta-results about classical logic. (shrink)

Many students ask, 'What is the point of learning formal logic?' This book gives them the answer. Using the methods of deductive logic, Nelson Lande introduces each new element in exquisite detail, as he takes students through example after example, proof after proof, explaining the thinking behind each concept. Shaded areas and appendices throughout the book provide explanations and justifications that go beyond the main text, challenging those students who wish to delve deeper, and giving instructors the option (...) of confining their course to the basics, or expanding it, when they wish, to more rigorous levels. Lande encourages students to think for themselves, while at the same time providing them with the level of explanation they need to succeed. It is a rigorous approach presented in a style that is informal, engaging, and accessible. Students will come away with a solid understanding of formal logic and why it is not only important, but also interesting and sometimes even fun. It is a text that brings the human element back into the teaching of logic. --Hans Halvorson, Princeton University. (shrink)