# Southern Summer Logic Day

# 2023

With the purpose of celebrating the UNESCO World Logic Day, the Australasian Association for Logic will host a **Southern Summer Logic Day**. The event will take place on Zoom (contact Guillermo Badia at g.badia@uq.edu.au for the Zoom link). There will be two keynote presentations, one by Graham Priest and one by David Makinson. The date and time will be Thursday, 12 January 2023 at 23:00:00 (UTC) (notice that in AU/NZ this will be a Friday 13, so beware). In addition to the keynotes, there will be three invited talks: Sasha Rubin (University of Sydney), Adriane Rini (Massey) and Alba Cuenca (Monash).

**Timetable **** (in **AEDT**, Friday 13 January****): **

** **

Graham Priest (Keynote): 10AM - 11:10AM

Sasha Rubin: 11:25AM - 12:30PM

Lunch break

Adriane Rini: 1:30PM - 2:30PM

Alba Cuenca : 2:45 PM- 3:45PM

David Makinson (Keynote): 4PM - 5:10 PM

**ORGANIZERS**

Guillermo Badia (University of Queensland, Australia)

Nick J J Smith (University of Sydney, Australia)

Shawn Standefer (National Taiwan University, Taiwan)

Koji Tanaka (Australian National University, Australia)

Graham Priest (Graduate Center, CUNY)

# Jaskowski and the Jains

In 1948 Jaśkowski introduced the first discursive logic. The main technical idea was to take what holds to be what is true at some possible world. Some 2,000 years earlier, Jain philosophers had advocated a similar idea, in their doctrine of *syādvād*a. Of course, these philosophers had no knowledge of contemporary logical notions; but the techniques pioneered by Jaśkowski can be deployed to make the Jain ideas mathematically precise. Moreover, Jain ideas suggest a new family of logics: many-valued discursive logics. In this talk, I will explain all these matters.

Sasha Rubin (University of Sydney)

# The automata-logic connection

This talk is a selective history of ideas on the tight relation between recognisability by computing devices and definability by logical formulas. I will focus on one such class of results that relates finite-state automata and monadic second-order logic. I will provide a survey of the basic concepts, results, and proofs. By way of applications of this theory, I will mention how it supplies optimal solutions to (Church's) synthesis problem, i.e., the problem of computing a program realising a given logical specification, which is finding application in artificial intelligence.

This talk aims to be self-contained for an audience with a background in elementary concepts in logic and computation, as found in typical undergraduate courses.

Adriane Rini (Massey)

# A Counterfactual History of Modal Logic

What do you think of when you think of the discovery of modal logic? Is it Aristotle’s syllogistic involving necessity, possibility, and contingency? Is it CI Lewis’s criticism of *PM*? Is it Oskar Becker’s different modal systems? Maybe Ruth Barcan Marcus’s modal predicate logic leaps to mind? Or maybe you’re the sort who grumbles along with WV Quine against the whole bad business? We can accept all of those as normal answers. But it’s a pretty safe bet that among the normal answers few would include 20th century feminist thought. This is a talk about what could have been.

The history of modal* *logic provides a case study of how logic and ideology connect, and the talk will illustrate this with respect to some recent feminist thought about modal logic.

Alba Cuenca (Monash)

# Proof-theoretic approaches to Epistemic Modal Logic

Epistemology, the study of knowledge, has a long and rich tradition in philosophy. Questions about what we know can be traced to early Greek philosophers. On the other hand, the formal study of the notion of knowledge is more recent. Thanks to developments in modal logic, propositional attitudes like “a knows φ” received a formal logical analysis, making use of the relational possible-worlds semantics. Epistemic modal logic is the result of this study, the branch of modal logic that deals with knowledge. This results in the usual focus in formal studies of knowledge being in terms of semantics. In this talk, I will defend a proof-theoretical approach to Epistemic Modal Logic. In particular, I will present a labelled goal-oriented proof-system.

(University of Queensland)

# Logic without Metaphysics

The theme of this talk is that in logic, metaphysical ideas can be useful as metaphors and initial stimulants, but they should be kept at an arm’s length, never taken literally. It is illustrated by four examples, taken from Boole (indefinite symbols), Frege (senses), possible worlds semantics (startreks and dialetheism) and proof-theoretic semantics (intelim harmony). Disagreement is expected.