Given a consequence relation in many-valued logic, what connectives can be defined? For instance, does there always exist a conditional operator internalizing the consequence relation, and which form should it take? In this paper, we pose this question in a multi-premise multi-conclusion setting for the class of so-called intersective mixed consequence relations, which extends the class of Tarskian relations. Using computer-aided methods, we answer extensively for 3-valued and 4-valued logics, focusing not only on conditional operators, but also on what we call Gentzen-regular connectives (including negation, conjunction, and disjunction). For arbitrary N-valued logics, we state necessary and sufficient conditions for the existence of such connectives in a multi-premise multi-conclusion setting. The results show that mixed consequence relations admit all classical connectives, and among them pure consequence relations are those that admit no other Gentzen-regular connectives. Conditionals can also be found for a broader class of intersective mixed consequence relations, but with the exclusion of order-theoretic consequence relations.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
Tax calculation will be finalised during checkout.
See Pogorzelski (1964) and Avron (1991) for more on the deduction theorem in relation to Łukasiewicz’s three-valued conditional. Pogorzelski shows that Łukasiewicz’s conditional satisfies a more complex form of the deduction theorem relative to consequence defined as the preservation of the value 1. Avron shows that it can satisfy the deduction theorem in standard form if the definition of logical consequence is modified in a way that rules out the above counterexample, by giving up structural contraction. We note that relative to the mixed consequence relation st (introduced below), Łukasiewicz’s conditional would satisfy the deduction theorem (but not what we call premise Gentzen-regularity, unlike with Avron’s consequence).
A recent exception is Wintein (2016) looking at 3-valued and 4-valued mixed consequence relations, but not at intersective mixed relations.
Computer-aided investigations of this kind still seem quite rare, which is striking considering that some pioneers such as Foxley (1962) had bravely started deploying them for very related tasks, when much more ingenuity was needed to compensate for the lower power of computers.
One may entertain other ways to extend an order on truth values (possibly with more properties, such as the systematic presence of infimums and/or supremums) onto a truth-relation between subsets of truth values. Below are some examples, close to descriptions in Chemla et al. (2017), but which we will not attend to specifically here: \(\gamma |\!\!\equiv \delta \) iff \(\inf (\gamma )\le \sup (\delta )\), or \(\gamma |\!\!\equiv \delta \) iff \(\exists d\in \delta : \inf (\gamma )\le d\).
Given an ordering \(\le \), an upset is a set that is closed under \(\le \), namely such that y belongs to the set whenever x belongs and \(x\le y\).
Gentzen originally stated only the right-to-left direction of those rules, but it is natural to use invertible rules.
This is not to imply that a regular connective may satisfy only one regularity rule. For instance, in reflexive logics, as in classical logic, adding a conjunct of the form \(\Gamma , A \vdash A, \Delta \) to a regularity rule produces a new rule, but it is essentially the same rule and certainly it is satisfied by the same connectives.
This conditional corresponds to a three-valued version of the so-called Gödel implication, see Hájek (1998).
Avron, A. (1991). Natural 3-valued logics: Characterization and proof theory. The Journal of Symbolic Logic, 56(1), 276–294.
Barrio, E., Rosenblatt, L., & Tajer, D. (2015). The logics of strict-tolerant logic. Journal of Philosophical Logic, 44(5), 551–571.
Belnap, N. D. (1977). A useful four-valued logic. In M. Dunn & G. Epstein (Eds.), Modern uses of multiple-valued logic (pp. 5–37). Berlin: Springer.
Blasio, C., Marcos, J., & Wansing, H. (2017). An inferentially many-valued two-dimensional notion of entailment. Bulletin of the Section of Logic, 46, 233–262.
Bonnay, D., & Westerståhl, D. (2012). Consequence mining: Constants versus consequence relations. Journal of Philosophical Logic, 41(4), 671–709.
Chemla, E., & Egré, P. (2019). Suszko’s problem: Mixed consequence and compositionality. Review of Symbolic Logic. https://doi.org/10.1017/S1755020318000503.
Chemla, E., Egré, P., & Spector, B. (2017). Characterizing logical consequence in many-valued logic. Journal of Logic and Computation, 27(7), 2193–2226.
Cobreros, P., Egré, P., Ripley, D., & van Rooij, R. (2012). Tolerant, classical, strict. Journal of Philosophical Logic, 41(2), 347–385.
Cobreros, P., Egré, P., Ripley, D., & van Rooij, R. (2015). Vagueness, truth and permissive consequence. In D. Achouriotti, H. Galinon, & J. Martinez (Eds.), Unifying the philosophy of truth (pp. 409–430). Berlin: Springer.
Cook, R. T. (2013). How to Read Grundgesetze. Appendix to G. Frege, Basic Laws of Arithmetic, ed. by P. Ebert and M. Rossberg, with C. Wright, Oxford University Press.
Foxley, E. (1962). The determination of all Sheffer functions in 3-valued logic, using a logical computer. Notre Dame Journal of Formal Logic, 3(1), 41–50.
Frankowski, S. (2004). Formalization of a plausible inference. Bulletin of the Section of Logic, 33(1), 41–52.
French, R., & Ripley, D. (2018). Valuations: bi, tri, and tetra. Studia Logica. https://doi.org/10.1007/s11225-018-9837-1.
Gentzen, G. (1935). Investigations into logical deduction. English translation in American Philosophical Quarterly, 1(4), 288–306, 1964 (Original Publication in Mathematische Zeitschrift 39 (1): 176–210).
Hájek, P. (1998). Metamathematics of fuzzy logic (Vol. 4). Berlin: Springer.
Jeffrey, R. C. (1963). On indeterminate conditionals. Philosophical Studies, 14(3), 37–43.
Kerkhoff, S., Pöschel, R., & Schneider, F. M. (2014). A short introduction to clones. Electronic notes in theoretical computer science. In Proceedings of the workshop on algebra, coalgebra and topology (WACT 2013), Vol. 303, pp. 107 – 120.
Łukasiewicz, J. (1920). On three-valued logic. English translation in J. Łukasiewicz, Selected Works, L. Borkowski ed., 1970. (Original Publication in Ruch Filosoficzny, 5, 70–71).
Malinowski, G. (1990). Q-consequence operation. Reports on Mathematical Logic, 24, 49–54.
Omori, H., & Sano, K. (2015). Generalizing functional completeness in Belnap–Dunn logic. Studia Logica, 103(5), 883–917.
Pogorzelski, W. (1964). The deduction theorem for Łukasiewicz many-valued propositional calculi. Studia Logica, 15, 8–19.
Priest, G. (1979). The logic of paradox. Journal of Philosophical logic, 8(1), 219–241.
Scott, D. (1974). Completeness and axiomatizability in many-valued logic. In Proceedings of the Tarski symposium, Vol. 25, American Mathematical Society, Providence, pp. 411–436.
Shoesmith, D. J., & Smiley, T. J. (1978). Multiple-conclusion logic. Cambridge: CUP Archive.
Shramko, Y., & Wansing, H. (2011). Truth and falsehood: An inquiry into generalized logical values (Vol. 36)., Trends in logic Berlin: Springer.
Steinberger, F. (2011). Why conclusions should remain single. Journal of Philosophical Logic, 40(3), 333–355.
Suszko, R. (1977). The Fregean axiom and Polish mathematical logic in the 1920s. Studia Logica, 36(4), 377–380.
Wintein, S. (2016). On all strong Kleene generalizations of classical logic. Studia Logica, 104(3), 503–545.
We are very grateful to Benjamin Spector for providing inspiration and support to this project. We thank two anonymous referees for detailed and helpful comments. We also thank Johan van Benthem, Denis Bonnay, Keny Chatain, Roy Cook, Christian Fermüller, João Marcos, Hitoshi Omori, Francesco Paoli, David Ripley, Lorenzo Rossi, Hans Rott, Philippe Schlenker, Jan Sprenger, Shane Steinert-Threlkeld, Heinrich Wansing for helpful conversations, as well as audiences in Regensburg (workshop “New Perspectives on Conditionals and Reasoning”, organized by H. Rott and C. Michel), Beijing (Tsinghua workshop “Logical in Theoretical Philosophy”, organized by A. Jiang, F. Liu, M. Stokhof), Bochum (Logic in Bochum IV, organized by H. Omori and H. Wansing), Dagstuhl (Dagstuhl Seminar 19032 “Conditional logics and conditional reasoning”, organized by G. Aucher, P. Egré, G. Kern-Isberner, F. Poggiolesi), and Buenos Aires (VIII Workshop on Philosophical Logic, organized by E. Barrio). The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 313610, and from the ANR program “Trivalence and Natural Language Meaning” (ANR-14-CE30-0010). We also thank the Ministerio de Economía, Industria y Competitividad, Gobierno de Espana, as part of the project “Logic and substructurality” (Grant FFI2017-84805-P), as well as grant FrontCog, ANR-17-EURE-0017 for research conducted in the Department of Cognitive Studies at ENS.
We dedicate this paper to the memory of Carolina Blasio.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Chemla, E., Egré, P. From many-valued consequence to many-valued connectives. Synthese (2019). https://doi.org/10.1007/s11229-019-02344-0
- Logical consequence
- Mixed consequence
- Many-valued logic
- Substructural logic
- Strict-Tolerant logic
- Algebraic logic
- Sequent calculus
- Deduction theorem
- Truth value