•  2
    A Note on Synonymy in Proof-Theoretic Semantics
    In Thomas Piecha & Kai F. Wehmeier (eds.), Peter Schroeder-Heister on Proof-Theoretic Semantics, Springer. pp. 339-362. 2024.
    The topic of identity of proofs was put on the agenda of general (or structural) proof theory at an early stage. The relevant question is: When are the differences between two distinct proofs (understood as linguistic entities, proof figures) of one and the same formula so inessential that it is justified to identify the two proofs? The paper addresses another question: When are the differences between two distinct formulas so inessential that these formulas admit of identical proofs? The questi…Read more
  •  21
    Constructive Logic is Connexive and Contradictory
    Logic and Logical Philosophy 1-27. forthcoming.
    It is widely accepted that there is a clear sense in which the first-order paraconsistent constructive logic with strong negation of Almukdad and Nelson, QN4, is more constructive than intuitionistic first-order logic, QInt. While QInt and QN4 both possess the disjunction property and the existence property as characteristics of constructiveness (or constructivity), QInt lacks certain features of constructiveness enjoyed by QN4, namely the constructible falsity property and the dual of the exist…Read more
  •  9
    Over the past ten years, the community researching connexive logics is rapidly growing and a number of papers have been published. However, when it comes to the terminology used in connexive logic, it seems to be not without problems. In this introduction, we aim at making a contribution towards both unifying and reducing the terminology. We hope that this can help making it easier to survey and access the field from outside the community of connexive logicians. Along the way, we will make clear…Read more
  •  12
    The book presents a thoroughly elaborated logical theory of generalized truth-values understood as subsets of some established set of truth values. After elucidating the importance of the very notion of a truth value in logic and philosophy, we examine some possible ways of generalizing this notion. The useful four-valued logic of first-degree entailment by Nuel Belnap and the notion of a bilattice constitute the basis for further generalizations. By doing so we elaborate the idea of a multilatt…Read more
  • Reerenz und Realität (edited book)
    with Rami A.
    mentis. 2007.
  •  25
    Logical Multilateralism
    with Sara Ayhan
    Journal of Philosophical Logic 52 (6): 1603-1636. 2023.
    In this paper we will consider the existing notions of bilateralism in the context of proof-theoretic semantics and propose, based on our understanding of bilateralism, an extension to logical multilateralism. This approach differs from what has been proposed under this name before in that we do not consider multiple speech acts as the core of such a theory but rather multiple consequence relations. We will argue that for this aim the most beneficial proof-theoretical realization is to use seque…Read more
  •  7
    On the Provable Contradictions of the Connexive Logics C and C3
    with Satoru Niki
    Journal of Philosophical Logic 52 (5): 1355-1383. 2023.
    Despite the tendency to be otherwise, some non-classical logics are known to validate formulas that are invalid in classical logic. A subclass of such systems even possesses pairs of a formula and its negation as theorems, without becoming trivial. How should these provable contradictions be understood? The present paper aims to shed light on aspects of this phenomenon by taking as samples the constructive connexive logic C, which is obtained by a simple modification of a system of constructible…Read more
  •  9
    On Synonymy in Proof-Theoretic Semantics: The Case of \(\mathtt{2Int}\)
    with Sara Ayhan
    Bulletin of the Section of Logic 52 (2): 187-237. 2023.
    We consider an approach to propositional synonymy in proof-theoretic semantics that is defined with respect to a bilateral G3-style sequent calculus \(\mathtt{SC2Int}\) for the bi-intuitionistic logic \(\mathtt{2Int}\). A distinctive feature of \(\mathtt{SC2Int}\) is that it makes use of two kind of sequents, one representing proofs, the other representing refutations. The structural rules of \(\mathtt{SC2Int}\), in particular its cut rules, are shown to be admissible. Next, interaction rules ar…Read more
  •  9
    Negation
    In Lou Goble (ed.), The Blackwell Guide to Philosophical Logic, Blackwell. 2017.
    This chapter is concerned with logical aspects of negation, i.e. with the role of negation in valid inferences and hence with the contribution negation makes to the truth and falsity conditions of declarative expressions. Negation is an important philosophical and logical concept. Often differences between logical systems can ‐ at least partially ‐ be described as differences between the notions of negation used in these logics.
  •  2
    Proofs and Expressiveness in Alethic Modal Logic
    with Maarten de Rijke
    In Dale Jacquette (ed.), A Companion to Philosophical Logic, Blackwell. 2006.
    This chapter contains sections titled: Introduction Model Theory Proof Theory Modal Predicate Logic.
  •  50
    40 years of FDE: An Introductory Overview
    Studia Logica 105 (6): 1021-1049. 2017.
    In this introduction to the special issue “40 years of FDE”, we offer an overview of the field and put the papers included in the special issue into perspective. More specifically, we first present various semantics and proof systems for FDE, and then survey some expansions of FDE by adding various operators starting with constants. We then turn to unary and binary connectives, which are classified in a systematic manner. First-order FDE is also briefly revisited, and we conclude by listing some…Read more
  •  34
    Kripke Completeness of Bi-intuitionistic Multilattice Logic and its Connexive Variant
    with Norihiro Kamide and Yaroslav Shramko
    Studia Logica 105 (6): 1193-1219. 2017.
    In this paper, bi-intuitionistic multilattice logic, which is a combination of multilattice logic and the bi-intuitionistic logic also known as Heyting–Brouwer logic, is introduced as a Gentzen-type sequent calculus. A Kripke semantics is developed for this logic, and the completeness theorem with respect to this semantics is proved via theorems for embedding this logic into bi-intuitionistic logic. The logic proposed is an extension of first-degree entailment logic and can be regarded as a bi-i…Read more
  •  21
    Varieties of entailment: introduction to the special issue
    Synthese 198 (S22): 5207-5211. 2020.
  •  93
    According to Suszko’s Thesis, there are but two logical values, true and false. In this paper, R. Suszko’s, G. Malinowski’s, and M. Tsuji’s analyses of logical twovaluedness are critically discussed. Another analysis is presented, which favors a notion of a logical system as encompassing possibly more than one consequence relation. [A] fundamental problem concerning many-valuedness is to know what it really is. [13, p. 281]
  •  34
    From the editors
    with Sergei Odintsov and Yaroslav Shramko
    Studia Logica 80 (2-3): 153-157. 2005.
  •  40
  •  28
    Preface
    with Max Urchs
    Logic and Logical Philosophy 3 (n/a): 45-46. 1995.
    Science today is an international business, of course, and there has hardly ever been a partition wall between the logical work in Poland and Germany. However, apart from long lasting personal scientific contacts there are good reasons to further intensify the relations between the German and the Polish Community of Logic and Logical Philosophy. So it was only natural to think about bringing them together at a scientific event in a friendly environment. This idea was carried out as a common init…Read more
  •  121
    The Slingshot Argument and Sentential Identity
    Studia Logica 91 (3): 429-455. 2009.
    The famous “slingshot argument” developed by Church, Gödel, Quine and Davidson is often considered to be a formally strict proof of the Fregean conception that all true sentences, as well as all false ones, have one and the same denotation, namely their corresponding truth value: the true or the false . In this paper we examine the analysis of the slingshot argument by means of a non-Fregean logic undertaken recently by A.Wóitowicz and put to the test her claim that the slingshot argument is in …Read more
  •  10
    Truth Values. Part I
    Studia Logica 91 (3): 429-455. 2009.
    The famous “slingshot argument” developed by Church, Gödel, Quine and Davidson is often considered to be a formally strict proof of the Fregean conception that all true sentences, as well as all false ones, have one and the same denotation, namely their corresponding truth value: the true or the false. In this paper we examine the analysis of the slingshot argument by means of a non-Fregean logic undertaken recently by A.Wóitowicz and put to the test her claim that the slingshot argument is in f…Read more
  •  116
    Some Useful 16-Valued Logics: How a Computer Network Should Think
    Journal of Philosophical Logic 34 (2): 121-153. 2005.
    In Belnap's useful 4-valued logic, the set 2 = {T, F} of classical truth values is generalized to the set 4 = (2) = {Ø, {T}, {F}, {T, F}}. In the present paper, we argue in favor of extending this process to the set 16 = ᵍ (4) (and beyond). It turns out that this generalization is well-motivated and leads from the bilattice FOUR₂ with an information and a truth-and-falsity ordering to another algebraic structure, namely the trilattice SIXTEEN₃ with an information ordering together with a truth o…Read more
  •  9
    The nature of entailment: an informational approach
    Synthese 198 (S22): 5241-5261. 2019.
    In this paper we elaborate a conception of entailment based on what we call the Ackermann principle, which explicates valid entailment through a logical connection between sentences depending on their informational content. We reconstruct Dunn’s informational semantics for entailment on the basis of Restall’s approach, with assertion and denial as two independent speech acts, by introducing the notion of a ‘position description’. We show how the machinery of position descriptions can effectively…Read more
  •  88
    Hyper-contradictions, generalized truth values and logics of truth and falsehood
    Journal of Logic, Language and Information 15 (4): 403-424. 2006.
    In Philosophical Logic, the Liar Paradox has been used to motivate the introduction of both truth value gaps and truth value gluts. Moreover, in the light of “revenge Liar” arguments, also higher-order combinations of generalized truth values have been suggested to account for so-called hyper-contradictions. In the present paper, Graham Priest's treatment of generalized truth values is scrutinized and compared with another strategy of generalizing the set of classical truth values and defining a…Read more
  •  10
    The paragraph starting with “By accepting condition only,...” should be read as follows
  • Knowability remixed
    In Colin R. Caret & Ole T. Hjortland (eds.), Foundations of Logical Consequence, Oxford University Press. 2015.
  •  9
    A Note on “A Connexive Conditional”
    Logos and Episteme 13 (3): 325-328. 2022.
    In a recent article, Mario Günther presented a conditional that is claimed to be connexive. The aim of this short discussion note is to show that Günther’s claim is not without problems.