Date Monday, 25 May 2026 at 15:00 CEST (UTC+2) on Zoom
Speaker Yanjing Wang (Professor of Logic, Peking University)
Title Bundled Fragments of First-order Modal Logic
Abstract
First-order modal logic (FOML) provides a natural logical language for reasoning
about modal attitudes, while retaining the richness of quantification for
referring to predicates over domains. However, FOML is notoriously bad
computationally, as most of the useful fragments of the logic are undecidable,
over many model classes. Over the years, only a few fragments (such as the
monodic fragment) have been shown to be decidable under heavy restrictions on
the syntax. In this talk, I survey our recent work on the newly discovered
bundled fragments based on constructions bundling quantifiers and modalities
together. The idea came from our earlier work on epistemic logics of
know-how/why/what, and it led us to many expressive and decidable fragments of
FOML without restricting the number of variables or the arity of the predicates.
I will give an almost complete picture of the (un)decidability of all the basic
bundled fragments of FOML over increasing and constant domain models. I conclude
with some future directions.
Date Monday, 27 April 2026 at 16:00 CEST (UTC+2) on Zoom
Speaker Ana Ozaki (Associate Professor, University of Oslo)
Title Model Change for Description Logic Concepts
Abstract
The field of Belief Change studies how an agent updates its beliefs in the
presence of new information. In this work, we consider the case where beliefs
are represented as description logic concepts and the new information is in the
format of pointed interpretations. We call this setting model change, and
distinguish three main kinds of changes: eviction, which consists of only
removing models; reception, which incorporates models; and revision, which
combines removal with incorporation of models in a single operation. We
introduce a formal notion of revision and argue that it does not reduce to a
simple combination of eviction and reception, contrary to intuition. We provide
positive and negative results on the compatibility of eviction and reception for
EL and ALC description logic concepts and on the compatibility of revision for
ALC concepts.
In 2026, the Scandinavian Logic Society Symposium (SLSS 2026) and Nordic Logic Summer School (NLSS 2026) organised under the auspices of the Scandinavian Logic Society will take place in Copenhagen!
The primary aim of the Symposium is to promote research in the field of logic (broadly conceived) carried out in research communities in Scandinavia. Moreover, it warmly invites the participation of logicians from all over the world. The meeting will include invited lectures and a forum for participants to present contributed talks.
Call for Abstracts: The scope of SLSS is broad, ranging over the whole areas of Mathematical and Philosophical Logic, as well as Logical Methods in Computer Science, Artificial Intelligence, Linguistics, among others. Major topics include (but are not limited to):
Submissions: Abstracts of contributed talks, in PDF format, not exceeding two A4
(11pt font) pages, should be submitted by 17 May 2026 (AoE) through EasyChair:
https://easychair.org/conferences/?conf=sls2026
Important dates:
Confirmed Invited Speakers:
Programme Committee:
We invite everyone interested in logic and its interface with philosophy, mathematics, computer science, and AI to participate in the Summer School. The intended audience for NLSS is advanced master students, PhD-students, post-docs and experienced researchers wishing to learn the state of the art in a particular subject. As usual, this year we have an exciting lineup of five lecturers on a wide spectrum of topics.
Confirmed NLSS 2026 Lecturers:
Important dates:
Programme Committee:
Both NLSS 2026 and SLSS 2026 are sponsored by the ASL. This means that any
student who wants to attend these events can apply for an ASL Student Travel
Award, to partially cover their expenses. Please note that to do so, the student
must be an ASL member and they must send their application to ASL by May 17th at
the latest. For more information and to apply for an ASL award, please follow
this link:
https://aslonline.org/student-travel-awards/
For more information about the SLSS and NLSS, contact the chair of the local organising committee Nina Gierasimczuk at nigi[at]dtu.dk
]]>Date Monday, 16 March 2026 at 16:00 CET (UTC+1) on Zoom
Speaker Yiannis Moschovakis (Professor of Mathematics Emeritus, University of Athens and UCLA)
Title Intensional semantics for formal and programming languages
Abstract
The claim is that intensions (or meanings) can be modeled usefully by algorithms
which compute truth values, proofs (in various systems), denotations and
implementations of programs (in various programming languages), etc.. I will
discuss the nature of these ‘algorithms’ and present some unpublished results by
me and others on this topic. Most of what I will say is in the book [1] which
contains many unpublished results by Lou van den Dries, Vaughn Pratt, Anush
Tserunyan and others.
[1] Yiannis Moschovakis. Abstract recursion and intrinsic complexity, Cambridge
University Press, Volume 48 in the Lecture Notes in Logic, Association for
Symbolic Logic, 2019. (See
YM’s homepage).
Date February 23, 16.00 CET (UTC+1)
Speaker Fan Yang, Assistant professor, Utrecht U
Title Possible and impossible conditionals for logics based on team semantics
Abstract
Team semantics is a semantic framework originally introduced by Hodges (1997)
for the study of dependence and independence concepts, and later systematically
developed by Väänänen (2007). It is also independently adopted in inquisitive
logic by Ciardelli and Roelofsen (2011). In team semantics, formulas are
evaluated with respect to sets of evaluation points, called teams, rather than
single evaluation points as in standard semantics.
Logics based on team semantics are typically extensions of classical logic and thus inherit classical implication over classical formulas. However, the earliest versions of team-based logic, such as independence-friendly logic and dependence logic, do not include a conditional connective for arbitrary formulas. An adequate conditional, known as intuitionistic implication, was proposed for dependence logic by Abramsky and Väänänen (2009). This connective is also part of the syntax of inquisitive logic. Intuitionistic implication behaves well in these downward closed logics, in the sene that it preserves downward closure and satisfies both Modus Ponens and the Deduction Theorem.
In recent years, many variants of dependence logic with different closure properties have been introduced, including union closed and convex logics. In these settings, the intuitionistic implication no longer behaves well, as it either fails to preserve the relevant closure property or fails to satisfy the Deduction Theorem. In this talk, we show that this failure is unavoidable: these logics cannot be enriched with any conditional connective that simultaneously preserves the closure property and satisfies both Modus Ponens and the Deduction Theorem.
This is joint work with Fausto Barbero.
]]>There will be plenary talks by
and tutorials by
There will also be sessions for contributed talks – see Abstract submission below.
The conference will include sessions for contributed talks. The talks will be 20 min long. If you are interested in contributing a talk, please send a title and a max 2 page abstract to estc2026@helsinki.fi with the subject “Abstract”, by the deadline of March 1, 2026.
February 18: Deadline for travel support applications
March 1: Deadline for contributed talk abstracts
March: Registration opens
March 13: Notification of acceptance of contributed talks
April 1: Deadline for early registration
May 18-22: ESTC2026
Student members of the Association for Symbolic Logic (ASL) may apply for travel support at ASL. Note that such applications have to be submitted at least 3 months prior to the meeting. For precise instructions on how to apply for ASL support, please see the ASL website https://aslonline.org/student-travel-awards/
In addition to the ASL travel awards, there is also some local funding available as travel support. To apply, send a mail to estc2026@helsinki.fi with the subject “Travel support” containing a motivation letter and an estimation of the support needed.
ESTC2026 website:
https://www.helsinki.fi/en/conferences/european-set-theory-conference
Conference email:
estc2026@helsinki.fi
Date Monday, 26 January 2026 at 16:00 CET (UTC+1) on Zoom
Speaker Henry Towsner (Associate Professor, University of Pennsylvania)
Title What proofs can be
Abstract
Throughout proof theory, proofs are often taken to be well-founded (often
finite) trees of inferences. Theories of inductive definitions, among other
theories, bump up against the limitations of this perspective, and a variety of
formalisms have been used to push beyond this - Girard’s beta-proofs,
non-well-founded proofs, proofs-as-functions. We briefly describe some features
of these approaches, the way these perspectives are essentially equivalent, and
the way well-foundedness reasserts itself as a core property of proofs.
Date Monday, 15 December 2025 at 16:00 CET (UTC+1) on Zoom
Speaker Phokion Kolaitis (Distinguished Research Professor, UC Santa Cruz and Principal Research Staff Member, IBM Almaden Research Center)
Title Possible Worlds and Certain Answers
Abstract
Databases are typically assumed to have definite content so that users can pose
queries and retrieve unambiguous answers. It is often the case, however, that a
database may contain information that is incomplete, inconsistent, or uncertain.
Possible world semantics provides meaning to logic-based queries on databases
suffering from these deficiencies. Such databases are viewed as compact
representations of all their possible rectifications; by definition, the certain
answers are the query answers that hold true in every possible rectification of
a deficient database.
The goal of this lecture is to provide an overview of some of the work on certain answers as a unifying framework for coping with incompleteness, inconsistency, and uncertainty in databases. Case studies include inconsistent databases, probabilistic databases, and election databases in social choice theory.
]]>April 3 – 5, 2026, Tsinghua University, Beijing.
For a fuller description of the workshop theme and other information, see the
web site:
https://tsinghualogic.net/JRC/tllm-2026
The TLLM workshops bring together logicians, philosophers, and linguists around a specific theme of common interest. For the 2026 event, the theme is unusually wide, and we welcome contributions on any general or particular aspect of the modalities in logic or language, such as:
1 Foundations and semantics of modality: E.g. Kripke/neighborhood/possibility/topological/game-theoretic/inquisitive/team semantics.
2 Proof theory for modal logic: E.g. sequent/natural deduction/labelled/circular/display/deep inference systems.
3 Epistemic and doxastic logics.
4 Deontic logic, norms and preference.
5 Modality in natural language: E.g. epistemic/deontic/dynamic modals; weak necessity and gradability; syntax of modals; semantic-pragmatic interface; cross-linguistic typology; experimental and corpus studies.
6 Non-classical perspectives on modality: E.g. intuitionistic/linear/relevant/paraconsistent/modal bilattice frameworks; bilateralist accounts.
7 Modality in computation, verification, and AI: E.g. KR with modalities; causal and probabilistic modal models; LLMs and modal reasoning (benchmarks, neurosymbolic methods, toolkits).
8 Modality and other intensional categories: e.g. modality and tense; modality and evidentiality; modality and mood.
9 The processing and acquisition of modal expressions in natural languages
Stefan Kaufmann (University of Connecticut)
Graham Leigh (University of Gothenburg)
Paul Portner (Georgetown University)
Jeremy Seligman (University of Auckland, Tsinghua University)
Yingying Wang (Hunan University)
Logic: Jeremy Seligman
Linguistics: Stefan Kaufmann
We invite submissions of 2-page abstracts (including references) on any of the broad themes related to modality** in logic and language as suggested above. After a review procedure, authors of accepted papers will be invited to present them at the workshop, either as a contributed talk or in the poster session. The poster session is intended to provide an informal setting for discussion and to encourage participation from early-career researchers and students. After the workshop, a volume of full papers (properly refereed) will be published in the Springer LNCS – FoLLI series. Details on submission of full papers will follow.
Abstracts should be submitted via Easychair:
https://easychair.org/conferences?conf=tllm2026
Deadline for submitting abstracts: November 15, 2025
Notification of acceptance: December 15, 2025
Tutorials: April 3, 2026
Workshop: April 3–5, 2026
Student: CNY 800
Non-student: CNY 1200
Maria Aloni (University of Amsterdam)
Johan van Benthem (University of Amsterdam, Stanford Univerisity, Tsinghua University)
Jowang Lin (Academia Sinica)
Fenrong Liu (Tsinghua University)
Xiaolu Yang (Tsinghua University)
Mingming Liu (co-chair, Tsinghua University)
Larry Moss (Bloomington, Indiana)
Stanley Peters (Stanford)
Jacopo Romoli (Heinrich Heine University Düsseldorf)
Martin Stokhof (ILLC, Tsinghua University)
Frank Veltman (ILLC)
Yingying Wang (Hunan University)
Dag Westerståhl (co-chair, Stockholm University, Tsinghua University)
Tomoyuki Yamada (Hokkaido University)
Jialiang Yan (China University of Political Science and Law)
Fan Yang (University of Utrecht)
Ting Xu (co-chair, Tsinghua University)
Linmin Zhang (NYU Shanghai)
Date Monday, 27 October 2025 at 16:00 UTC+1 on Zoom
Speaker Monday, 29 September 2025 at 16:00 CEST (UTC+2) on Zoom
Title Decomposing Arrows with Parity
Abstract
The idea of articulating a propositional logic that adds a relevance-sensitive
implication connective to the usual truth-functional ones has been approached in
many ways, e.g. using axioms and derivation rules, natural deduction systems,
possible worlds or states equipped with relations or operations, algebraic
structures, consecution systems etc. None are very satisfactory. In the 1970s,
semantic decomposition trees (aka truth-trees, semantic tableaux, analytic
tableaux) were briefly considered, but they did not get far and were swept away
by the tsunami of Routley/Meyer possible worlds with ternary relations. We renew
that approach using a notion of parity for the branches of a tree or,
alternatively, an even more global one of sibling-parity for the entire tree.
There are some nice results and, above all, some big open questions.