Logic and Logical Philosophy

On the Axiom of Canonicity

Jerzy Pogonowski — 2022-07-07

The axiom of canonicity was introduced by the famous Polish logician Roman Suszko in 1951 as an explication of Skolem's Paradox (without reference to the L\"{o}wenheim-Skolem theorem) and a precise representation of the axiom of restriction in set theory proposed much earlier by Abraham Fraenkel. We discuss the main features of Suszko's contribution and hint at its possible further applications.

Grounding and Propositional Identity: A Solution to Wilhelm’s Inconsistencies

Francesca Poggiolesi — 2022-03-09

By following a recent result of [Wilhelm, 2021], it can easily be shown that standard conditions for immediate partial grounding and relevant identity conditions for propositions are inconsistent with one another. This is an unfortunate situation for all grounding enthusiasts; however, by adopting the approach presented by Poggiolesi [2016a,b], which displays a more-fined grained use of negations, it can also be shown that consistency can be restored back.

Counterparts, Essences and Quantified Modal Logic

Tomasz Bigaj — 2022-01-10

It is commonplace to formalize propositions involving essential properties of objects in a language containing modal operators and quantifiers. Assuming David Lewis’s counterpart theory as a semantic framework for quantified modal logic, I will show that certain statements discussed in the metaphysics of modality de re, such as the sufficiency condition for essential properties, cannot be faithfully formalized. A natural modification of Lewis’s translation scheme seems to be an obvious solution but is not acceptable for various reasons. Consequently, the only safe way to express some intuitions regarding essential properties is to use directly the language of counterpart theory without modal operators.

Varieties of Relevant S5

Shawn Standefer — 2022-03-08

In classically based modal logic, there are three common conceptions of necessity, the universal conception, the equivalence relation conception, and the axiomatic conception. They provide distinct presentations of the modal logic S5, all of which coincide in the basic modal language. We explore these different conceptions in the context of the relevant logic R, demonstrating where they come apart. This reveals that there are many options for being an S5-ish extension of R. It further reveals a divide between the universal conception of necessity on the one hand, and the axiomatic conception on the other: The latter is consistent with motivations for relevant logics while the former is not. For the committed relevant logician, necessity cannot be the truth in all possible worlds.

How to Get out of the Labyrinth of Time? Lessons Drawn from Callender

Jerzy Gołosz — 2022-04-22

Callender [2017] claims that contemporary science demonstrates that there is no objective present and no objective flow of time, especially since all sensed events come from the past, our various senses need different amounts of time to react, and there are enough asymmetries in the physical world to explain our experience of time. This paper holds that, although Callender’s arguments for the subjectivity of the flow of time are unconvincing, the scientific discoveries and arguments he indicates can still be applied to improve theories of the objective flow of time. The paper develops precisely such a theory, one which introduces multiple individual proper presents for all of the objects that make up our world.

Equality and Near-Equality in a Nonstandard World

Bruno Dinis — 2022-05-21

In the context of nonstandard analysis, the somewhat vague equality relation of near-equality allows us to relate objects that are indistinguishable but not necessarily equal. This relation appears to enable us to better understand certain paradoxes, such as the paradox of Theseus’s ship, by identifying identity at a time with identity over a short period of time. With this view in mind, I propose and discuss two mathematical models for this paradox.

A Leibnizian Logic of Possible Laws

Kordula Świętorzecka — 2022-05-06

The so-called Principle of Plenitude was ascribed to Leibniz by A. O. Lovejoy in The Great Chain of Being: A Study of the History of an Idea (1936). Its temporal version states that what holds always, holds necessarily (or that no genuine possibility can remain unfulfilled). This temporal formulation is the subject of the current paper. Lovejoy’s idea was criticised by Hintikka. The latter supported his criticisms by referring to specific Leibnizian notions of absolute and hypothetical necessities interpreted in a possible-worlds semantics. In the paper, Hintikka’s interpretative suggestions are developed and enriched with a temporal component that is present in the characteristics of the real world given by Leibniz. We use in our approach the Leibnizian idea that change is primary to time and the idea that there are possible laws that characterize worlds other than the real one. We formulate a modal propositional logic with three primitive operators for change, temporal constancy, and possible lawlikeness. We give its axiomatics and show that our logic is complete with respect to the given semantics of possible worlds. Finally, we show that the counterparts of the considered versions of the Principle of Plenitude are falsified in this semantics and the same applies to the counterpart of Leibnizian necessarianism.

Fidel Semantics for Propositional and First-Order Version of the Logic of CG’3

Aldo Figallo Orellano — 2022-05-24

Paraconsistent extensions of 3-valued Gödel logic are studied as tools for knowledge representation and nonmonotonic reasoning. Particularly, Osorio and his collaborators showed that some of these logics can be used to express interesting nonmonotonic semantics. CG’₃is one of these 3-valued logics. In this paper, we introduce Fidel semantics for a certain calculus of CG’₃by means of Fidel structures, named CG’₃-structures. These structures are constructed from enriched Boolean algebras with a special family of sets. Moreover, we also show that the most basic CG’₃-structures coincide with da Costa–Alves’ bi-valuation semantics; this connection is displayed through a Representation Theorem for CG’₃-structures. By contrast, we show that for other paraconsistent logics that allow us to present semantics through Fidel structures, this connection is not held. Finally, Fidel semantics for the first-order version of the logic of CG’₃are presented by means of adapting algebraic tools.