Monday April 22nd 2013
Philosophy Department, RUC 
starting at 13:00.

13.00     Henning Christiansen:  
                Abductive reasoning made easy with logic programming with constraints (Abstract below)

13.45     Kevin Kelly: 
                A Learning Semantics for Inductive Knowledge (Abstract below)

14.30     Coffee Break

14.45     Sonja Smets and  Alexandru Baltag: 
                Paradox, Belief Change and Fixed Points: 
                or How to Avoid Unexpected Exams (Abstract below)

15.45     Wine


The four speakers are:

Kevin Kelly - 
A Learning Semantics for Inductive Knowledge
ABSTRACT:
Knowledge evidently has something to do with inquiry: the evolution of belief in light of increasing information.  Wouldn’t it be nice if the modal semantics of epistemic logic included all of those obvious components, along with an account of what inductive knowledge is?  Then its  models would not merely represent what is knowable---they would explain how it is knowable.  They would also explain whether and how one can know what is not learnable, know that one knows, know that one doesn’t know or know the consequences of what one knows.  They could also explain how teachers can transfer scientific knowledge to gullible students  and how a kernel of scientific knowledge can erupt into common scientific knowledge in a gullible community.   One of the leading ideas in the semantics is that inductive learnability is not necessary for inductive knowability.  Knowledge allows for serendipitous luck in selecting a learnable reason for believing a theory that is not itself learnable.    The talk builds upon discussions decades ago with Stig Andur Pedersen and Vincent Hendricks, so it is a pleasure to present it at Roskilde.


Henning Christiansen 
Abductive reasoning made easy with logic programming with constraints
ABSTRACT:
Abductive reasoning, or "abduction", means to find a best explanation for some unexpected observation. In a logical setting, an explanation can be a set of facts which, when added to our current knowledge base, makes it possible to prove the truth of the observation and, at the same time, is not inconsistent with the knowledge base.

Introduced by Peirce, the notion has attracted much attention in philosophy, detective stories and computer science, most notably in logic programming. Until the shift of the millennium, abduction in logic programming was realized through complex meta-interpreters written in Prolog, which may have led to a view of abduction as being some hairy, difficult stuff, far too inefficient for any realistic applications. In this talk, we demonstrate how a fairly powerful version abductive reasoning can be exercised through a direct use of Prolog, using its extension by Constraint Handling Rules as the engine to take care of abducible hypotheses.


Sonja Smets & Alexandru Baltag 
Paradox, Belief Change and Fixed Points: 
or How to Avoid Unexpected Exams
ABSTRACT:
We develop a theory of dynamic-doxastic attitudes, modeling in a qualitative manner various forms of trust/distrust in the reliability of a source of information. Formally, such attitudes correspond to doxastic transformers, i.e. ways of changing doxastic/plausibility models with any new piece of information originating in the given source. We argue that the fixed points of these transformers play a central role in solving various epistemic puzzles, such as the Surprise Exam Paradox

10 am at DTU in room 030, building 322.
Technical University of Denmark

Abstract: Dynamic Epistemic Logic (DEL) deals with the representation  and the
study in a multi-agent setting of knowledge and belief change.
It can express
in a uniform way epistemic statements about:
\begin{enumerate}
\item[(i)]
what is true about an initial situation
\item[(ii)] what is true about an
event occurring in this situation
\item[(iii)] what is true about the
resulting situation after the event has occurred.
\end{enumerate}
We
axiomatize within the DEL framework what we can infer about (iii)  given (i) and
(ii), what we can infer about (ii) given (i) and (iii),  and what we can infer
about (i) given (ii) and (iii). These three  inference problems are related to
classical problems addressed under  different guises in artificial intelligence
and theoretical computer  science, which we call respectively progression,
epistemic planning and  regression. Given three formulas $\phi$, $\phi'$ and
$\phi''$ describing respectively (i), (ii) and (iii), we also show how to build
three  formulas $\phi\otimes\phi'$, $\phi\varoslash\phi''$ and
  $\phi'\varobslash\phi''$ which capture respectively all the information  which
can be inferred about (iii) from $\phi$ and $\phi'$, all the  information which
can be inferred about (ii) from $\phi$ and $\phi''$,  and all the information
which can be inferred about (i) from $\phi'$ and $\phi''$. We show how our
results extend to other modal logics than  $\logicK$. In our proofs and
definitions, we resort to a large extent to the normal form formulas for modal
logic originally introduced by Kit  Fine.

Thursday 28 June 2012
Roskilde University
14:00

(This is joint work with Tim French, Fernando Velazquez, and Yi Wang)
We consider semantic structures and logics that differentiate between being uncertain about a proposition, being unaware of a proposition, becoming aware of a proposition, and getting to know the truth value of a proposition. We propose a unified setting to model this variety of static and dynamic aspects of awareness and knowledge. Various derived notions will be discussed: explicit knowledge, implicit knowledge, and also novel epistemic notions such as speculative knowledge (back to the motivation in Levesque's 'A Logic of Implicit and Explicit Belief', one can speculate over variables of which one is unaware, e.g. if you are unaware of p, then p v ~p is still speculatively known by you). A cornerstone of this framework is the notion of awareness bisimulation - this is the proper notion of structural similarity on the structures enriched with awareness of propositional variables proposed by Fagin and Halpern in 'Belief, awareness, and limited reasoning'. Just as bisimilarity preserves logical truth, awareness bisimilarity preserves the truth of which you are aware.

Tuesday 26 June 2012
at 13.00, Hans van Ditmarsch will give a talk on "refinement modal logic" at the Technical University of Denmark (building 305, room 053).  His visit is hosted by Thomas Bolander, Technical University of Denmark, and the trip is sponsored by the HYLOCORE project. Please see the attached pdf file for abstract and details.

Modality and Modalities  is a two day CADILLAC event on all things Modal Logical. It will be held on Tuesday, 29th May and Wednesday, 30th May at the University of Copenhagen. The keynote speakers are  Max Cresswell, Adriane Rini, and there will be a special tutorial presentation by Valentin Goranko.

All are welcome to attend, and attendance is free. But please: email us at here at CADILLAC if you plan on coming, so that we have some idea of how many to expect!

Contributors:
Martin Mose Bentzen, Patrick Blackburn, Thomas Bolander, Torben Braüner, Max Cresswell, Sebastian Enqvist, Emmanuel Genot, Justine Jacot, Mikkel Gerken, Valentin Goranko, Jens Ulrik Hansen, Klaus Frovin Jørgensen, Peter Øhrstrøm, Carlo Proietti, Rasmus K. Rendsvig, Adrianne Rini, Krister Segerberg    

Tuesday, 24 April 2012
(week17), 11.00 - 13.00
University of Copenhagen / Humanities / Southern Campus
Room 24.2.01
-------------------------
Ockham's Razors

Kevin T. Kelly and Hanti Lin
Carnegie Mellon University

Ockham's razor is perhaps the most characteristic principle of
scientific theory choice.  Ever since the principle played a major role
in the Copernican revolution, it has occasioned two perennial
questions:
 (1) what is empirical simplicity? and (2) why should someone
interested in finding true theories favor simpler theories?   We propose
new, logical answers.   We explicate simplicity in terms of the logical
structure of a question under discussion and then argue that various
versions of Ockham's razor are optimally truth-conducive, depending on
how one conceives of optimal convergence to the truth.  The resulting
Ockham's razors are similar to and yet distinct from standard theories
of belief revision.   Also, Gettier-like considerations emerge directly
from truth-conduciveness.  The talk should interest anyone concerned
with scientific method and rationality.

Jens Ulrik Hansen from Roskilde University will give a talk:

24 February 2012
11:30-13:00 in building 322, room 030, at DTU (Technical University of Denmark).

Title:  Enhancing fitness and flexibility of logic-based models of knowledge and beliefs

Abstract:  There are several inherited limitations of classical epistemic logic leading to well known paradoxes such as logical omniscience, which derives from the fact that the scenario/the epistemic possible world model is common knowledge among the involved agents. The aim of my Carlsberg project (1 year post.doc. to be carried out at ILLC, Amsterdam) is to investigate the possibility of partial versions of epistemic logic that allows for the entering of new facts and agents into possible world models. The basic idea is inspired by Dynamic Epistemic Logic, where modalities that can change possible world models are introduced. Since my project is not yet started, I do not have any final results yet. Thus the talk will mostly be a presentation of some of the ideas and different approaches, which I intend to investigate in the project.

17 Fevrier 2012
We'll be in room  27.0.47 at KUA on Njalsgade 80, 2300 KBH S.

9:00 Morning Coffee and Chat
9:15 Olivier Roy
10:15 Coffee
10:30: Pelle Guldborg Hansen
11:25 Short coffee
11:30 Rasmus K. Rendsvig
12:30 Lunch
14:00 Sine Zambach
15:00 Coffee
15:15 Jens Ulrik Hansen
16:15 Coffee
16:30 Carlo Proietti