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Logical Pluralism

09.10.2023 – 10.10.2023

Idea and Motivation

Logical pluralism has received some attention in recent years. Although already Carnap’s famous principle of tolerance promises a form of logical pluralism the topic has been put into focus by Beall and Restall´s monograph. In recent years the discussion has evolved from the question of one true logic versus a plurality of logics to a diverse field of questions. These include questions of the correct formulation of logical pluralism, its purported coherence, connections to normativity and relativism.

The workshop brings together experts in the field as well as PhD students working in this area. The workshop is part of the DFG project Logics, from tolerance to pluralism.



Time Event
Monday,  October 9
09:15-09:30 Welcome
09:30-10:30 Alessandra Marra and Matteo De Benedetto: Logical norms, defeasible obligations, and pluralistic stances
10:30-10:45 Coffee Break
10:45-11:45 Hosea von Hauff: The Truth, and Nothing but the Truth
11:45-14:00 Lunch Break
14:00-15:00 Erik Stei: The Metalogic Objection to Logical Pluralism
15:00-16:00 Rodrigo Mena: Carnap´s Pluralism and the Underdetermination of Consequence Relations
16:00-16:15 Coffee Break
16:15-17:15 Martin Fischer: "The" Logic of Significance?
19:00 Workshop Dinner
Tuesday, October 10
10:00-11:00 Julien Murzi and Brett Topey: Pluralism by Convention
11:00-11:15 Coffee Break
11:15-12.15 Sophie Nagler: Meaning as Use, Use as Meaning
12:15-14:15 Lunch Break
14:15-15:15 Tyko Schuff: Logic beyond truth preservations
15:15-15:30 Coffee Break
15:30-16:30 Gil Sagi: What is and what should never be: Conventionalism and the availability of alternative logics
16:30-17:00 Discussion



Alessandra Marra and Matteo De Benedetto: Logical norms, defeasible obligations, and pluralistic stances

We start by defending a picture of logical normativity according to which the norms that logic imposes on reasoning are understood as defeasible obligations. Building upon theories of bounded rationality, our approach conceptualizes reasoning as constrained by multiple,
independent norms, logical and non-logical ones. These different norms are often in conflict with one another, to the effect that defeasible logical obligations on what to believe do not always coincide with what an agent ought to believe all things considered. From this perspective, we critically assess which forms of logical pluralism can emerge.

Hosea von Hauff: The Truth, and Nothing but the Truth

Instrumentalism about logic, as discussed in the recent literature, is the position that a logic is legitimate if it has a useful application, or has a legitimate goal, and moreover, that there is more than one such legitimate goal. This results in a form of logical pluralism that has thus far not been taken all too seriously. We want to explore a modification to this position, that, if successful, would give an interesting story on how it is possible for logic(s) to still be normative for reasoning, without ending up with a stripe of domain-relative pluralism. This will come at the cost of giving up on the idea that logic(s) need be about truth (or rather truth preservation) and nothing else.

Eric Stei: The Metalogic Objection to Logical Pluralism

Logical pluralism is the claim that there is more than one correct logic. But which of these logics may the pluralist use when engaged in metalogical reasoning – for instance, when proving that logics have a certain property, or defending the pluralist thesis itself? Critics have argued that pluralists have no convincing story to tell (Griffiths & Paseau 2023, Sereni & Sforza Fogliani 2020). In the talk, I review the metalogic objection with a focus on the justificatory challenge for logical pluralism. I argue that at least some aspects of the challenge can be met. In particular, the justification of pluralism by non-deductive means – a strategy favoured by prominent pluralists themselves – may fare better than its critics admit.

Rodrigo Mena: Carnap's Pluralism and the Underdetermination of Consequence Relations

The main goal of this presentation is to show that, contrary to some opinions from the literature, the philosophy of logic that Carnap defended in The Logical Syntax of Language (LSL) may be interpreted in a pluralistic manner. Some aspects of the notion of 'consequence relation' underlying LSL and the underdetermination of such relations provide the opportunity to describe different logics (with incompatible rules of inference) for the same logical theory in his framework and, perhaps, to other logical theories too. This means that his philosophy might not be committed to a unique logic when defining a formal language, but to the conditions of that logic to be expressed in that language. So, the introduction of different predicates describing different derivability relations in LSL and the fact that there is no other internal criterion in Carnap's philosophy to determine whether a logic is correct may be enough to consider him as a pluralist.

Martin Fischer: ‘The’ logic of significance?

Logic is supposed to provide a suitable formal model of reasoning and therefore inferences are in the focus of interest. In some discourses there is the possibility of sentences failing to express a proposition not being significant. The question of the correct logic for such discourses, preserving significance, is of great interest. Following Reinhardt 1986 the Kripkean conception of type-free truth is a special case. In the talk I will discuss the role of different logics in this context. I will argue that there is not one single 'correct’ logic, but that a plurality of logics is the most informative for an interpretation of significant reasoning.

Julien Murzi and Brett Topey: Pluralism by Convention

We assume, with Putnam, that the interpretation of a logical expression $ is fully determined by the way we use $. We then argue for two main claims: first, that such a broadly inferentialist metasemantic assumption strongly favours a broadly Carnapian form of pluralism; and, second, that it also tells against pluralist conceptions, such as the one advocated by Beall & Restall, that postulate the availability of different meanings for the same logical expressions within the same language

Sophie Nagler: Meaning as Use, Use as Meaning

In this talk, I propose an explication of ‘connective meaning’ centred around the inferential behaviour of connectives. I show how to implement this idea for the LK-family of logics, including classical, intuitionistic, dual-intuitionistic, minimal, and lattice logic. Based on Bogdan Dicher’s 2016 co-determination thesis, I systematically determine which operational or structural components of a sequent calculus can be viewed as meaning-defining. I utilise this use-theoretic account to defend a version of meaning-invariant logical pluralism. This way, I contend, we can avoid some of the potential shortcomings of Beall and Restall’s 2006 pluralism.

Tyko Schuff: Logic beyond truth-preservation

The valid inferences of classical logic preserve truth from premises to conclusion. We will argue that non-classical logics are concerned with more than just mere truth-preservation. In addition to preserving truth, they also preserve other properties from premises to conclusion. This observation raises several questions regarding meaning-variance and logical pluralism.

Gil Sagi: What is and what should never be: Conventionalism and the availability of alternative logics

Conventionalism is often presented as a form of pluralism. The most recent extensive defence of logical conventionalism is by Jared Warren, who claims that his conventionalism entails logical pluralism. In the main, first part of the talk I shall take issue with this claim. In a nutshell, Warren's naturalistic, metaphysically lightweight conventionalism is not enough to entail the demanding pluralism to which he is committed---his arguments at most show that conventionalism and pluralism are consistent. The point is significant because it bears on fundamental questions on the nature of language. In the second part of the talk, as time permits, I'll explore a different kind of conventionalism, of a more Carnapian flavor, and how it may relate to logical pluralism.



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