• [2017-04-24 Mon] Jesse and Christian got their paper Revisiting Unrestricted Rebut and Preferences in Structured Argumentation. accepted for IJCAI 2017.
• [2017-04-11 Tue] Christian and Dunja gave a talk introducing the NMLFA and recent research results at the Workshop on Formal Argumentation in Online Discussions at the Institute for Computer Science, Heinrich Heine University.
• [2017-04-05 Wed] Jesse gave a talk on Reasoning by Cases in Structured Argumentation at the track on Knowledge Representation and Reasoning of the 32nd ACM SIGAPP Symposium On Applied Computing in Marrakech on 2017-04-5.
• [2017-03-06 Mon] There is a 2nd call for abstract for our forthcoming conference on Formal Models of Scientific Inquiry is out.
• [2017-03-04 Sat] Christian gave a talk on Reasoning Defeasibly by Cases at the Logics of Consequence workshop at Concordia University, Montreal. link
• [2017-03-01 Wed] The deadline for the submissions special issue on Argument Strength has been extended to March 31, 2017.
• [2017-02-03 Fri] The call for Formal Models of Scientific Inquiry is out. See link and https://easychair.org/cfp/FMSI-2017.
• [2017-01-16 Mon] The call for the Argument Strength 2016 - Special Issue in IfCoLog is out. https://easychair.org/cfp/ArgStr16-Special-Issue
• [2017-01-16 Mon] The call for Logic in Bochum III is out: here.
• [2017-01-11 Wed]–[2017-01-13 Fri] Martin Caminada (Cardiff) was a guest at our group. He gave a talk at the Colloquium of the Institute for Philosophy II on Open Research Challenges in Formal Argumentation and another talk in the research colloquium on Logic and Epistemology on A Discussion Game for Grounded Semantics.
• more changes

Welcome at the homepage of the Research Group for Non-Monotonic Logics and Formal Argumentation. We are a young research group situated at the Ruhr-University Bochum, Institute for Philosophy II. The group was started on 1st of January 2015.

The group is supported by a Sofja Kovalevskaja award in 2014 of the Alexander von Humboldt-Foundation, funded by the German Ministry for Education and Research.

You can find an outline of the broader research project of the group here.

## Members

Currently the group hosts the following researchers:

AnneMarie Borg (PhD-candidate, funded by the Humboldt-foundation, office GA 3/155)
AnneMarie has been working on Justification Logic and Sequent Calculi. Her academic profile can be found here. Her PhD is supervised by Christian and Ofer Arieli.

Jesse Heyninck (PhD-candidate, funded by the Humboldt-foundation, office GA 3/155)
He's doing a PhD under the supervision of Ofer Arieli and Christian Straßer. He's especially interested in combinations of defeasible reasoning forms and argument strength (here's a description of his research project). His homepage can be found here and his CV here.

Mathieu Beirlaen (Post-Doc, funded by the Humboldt-foundation, office GA 3/155)
Mathieu is working on ampliative reasoning (abduction, inductive generalizations), deontic logic, adaptive logic. Find more information on his homepage, including a list of publications.

Dunja Šešelja (Post-Doc, funded by RUB, office GA 3/39)
Dunja is working in the philosophy of science. She's especially interested in disagreements among scientists from an epistemological and methodological perspective. She's also a visiting professor at Ghent University. You find her CV here, her list of publications here and her list of talks here. Find more information on her academic homepage. Her speaking hours are every Wednesday from 14:00–16:00 (best write her a mail first).

Pere Pardo Ventura (Post-Doc, funded by the Humboldt-foundation, office GA 3/155)
Pere is working on applications of argumentation and dynamic epistemic logic into defeasible reasoning and deontic logic. A brief CV and list of publications can be found in his homepage https://sites.google.com/site/perepardoventura/home You can write him at pere.pardoventura@mail.ruhr-uni-bochum.de

Christian Straßer (Jun.-Prof., funded by the Humboldt-foundation, office GA 3/39)
Christian is working in non-monotonic logics, defeasible reasoning, argumentation, deontic and adaptive logics. He's also a visiting professor at Ghent University. His CV is here, his list of publications here and his talks ahere. For more information take a look at his academic homepage. His speaking hours are every Wednesday from 10:00–12:00 best write him a mail first. You can write him at christian.strasser@ruhr-uni-bochum.de

## Recent and Upcoming Events and Talks

### Upcoming Events and Talks

• [2017-04-26 Wed]
Dunja will give a talk at the MCMP on Using Abstract Argumentation for Agent-Based Modeling of Scientific Inquiry (joint work with AnneMarie Borg, Daniel Frey and Christian Straßer).
• PhDs in Logic IX (May 2-4, 2017)
The workshop is co-located with the graduate conference PhDs in Logic IX which takes place right before Logic in Bochum III (2nd-4th May 2017). Attendance is free but please register. For more info, see: http://www.ruhr-uni-bochum.de/phdsinlogicix/index.php
• Logic in Bochum III (May 5-6, 2017. Submission deadline: March 15, 2017)
The annual workshop Logic in Bochum gathers logicians from different domains for a two days workshop at Ruhr University Bochum. This year it will take place on the 5th and 6th of May. The workshop traditionally consists of two parts: the first part (day 1), devoted to a specific area of logic and the second part (day 2) devoted to a variety of topics. We invite submissions of abstracts for the first part of the workshop, which this year focuses on deontic logics. For more information see link.
• Conference "Formal Models of Scientific Inquiry" (July 18-19, 2017. Submission deadline: April 1, 2017)
Throughout the last two decades philosophical discussions on scientific inquiry have increasingly utilized formal models. This has been especially fruitful for the investigation of social aspects of scientific inquiry, such as the division of cognitive labor, social factors that influence scientific decision making, etc. To this end a variety of formal models have been developed, starting from analytical ones to agent-based models that provide computer simulations of scientific inquiry. One of the main advantages of formal approaches is that they help us to understand these issues precisely and to form normative generalizations that are difficult to obtain in view of traditional methods (such as, for example, historical case studies). Nevertheless, models frequently come with a high degree of idealization and simplification, which may impede their relevance for actual scientific practice. This poses the question, to which extent formal models can be used to provide an understanding of scientific inquiry, and to which extent they can be improved with respect to their relevance for science policy. For more information see link.

### Recent Events and Talks

• [2017-04-11 Tue]
Christian and Dunja gave a talk introducing the NMLFA and recent research results at the Workshop on Formal Argumentation in Online Discussions at the Institute for Computer Science, Heinrich Heine University.
• [2017-04-05 Wed]
Jesse gave a talk on Reasoning by Cases in Structured Argumentation at the track on Knowledge Representation and Reasoning of the 32nd ACM SIGAPP Symposium On Applied Computing in Marrakech on 2017-04-5.
• [2017-03-04 Sat]
Christian gave a talk on Reasoning Defeasibly by Cases at the Logics of Consequence workshop at Concordia University, Montreal. link
• [2017-01-12 Thu]
Martin Caminada gave a talk in the Colloquium for Logic and Epistemology on the topic A Discussion Game for Grounded Semantics.
• [2017-01-11 Wed]
Martin Caminada was guest at the Colloquium for the Institute for Philosophy II and gave a talk on Open Research Challenges in Formal Argumentation.
• [2016-11-30 Wed]–[2016-12-02 Fri]
We were organizing a workshop on Argument Strength at the Institute for Philosophy II (RUB). You find the webpage here

Workshop on argument strength

Ruhr University Bochum (RUB), October 30 – December 2, 2016

Arguments vary in strength. The strength of an argument is affected by e.g. the plausibility of its premises, the nature of the link between its premises and conclusion, and the prior acceptability of the conclusion.

The aim of this workshop is to bring together experts from the fields of artificial intelligence, philosophy, logic, and argumentation theory to discuss questions related to the strength of arguments. Such questions include:

• Which factors influence the strength of an argument?
• What are the pros and cons of different formal representations of argument strength?
• How to formally model qualifiers on the conclusions of arguments?
• How does argument strength propagate when inferences are chained?
• How do arguments accrue?
• Can weaker arguments defeat and/or defend stronger arguments?
• When do more specific arguments defeat more general arguments and vice versa?
• How do formal and informal approaches to argument strength relate?
• How do preferences assigned to premises influence the evaluation of arguments?

Authors are invited to submit abstracts (500-1000 words) related to these or any other questions on the topic argument strength to mailto:argumentstrength2016@gmail.com.

Important dates:

• [2017-05-02 Tue]–[2017-05-04 Thu]
AnneMarie and Jesse co-organize the upcoming PhDs in Logic event at RUB. More information can be found here.
• [2016-11-22 Tue]
Dunja gave a talk on Using Abstract Argumentation for a More Adequate Agent-Based Modeling of Scientific Inquiry at Leibniz Universität Hannover
• [2016-10-21 Fri]
AnneMarie, Dunja and Christian Straßer gave a talk on An argumentative agent-based model of scientific inquiry at the Workshop "Agent Based Modelling across Social Science, Economics, and Philosophy" in Bamberg, Germany
• [2016-09-23 Fri]
AnneMarie, Dunja and Christian gave a talk in Belgrade at the PSX5 on An argumentative agent-based model of scientific inquiry
• [2016-09-21 Wed]
Pere gave a talk on t-DeLP: Temporal Defeasible Logic Programming at the Workshop on Modal Logic and its Application in Computer Science in Tehran.
• [2016-09-08 Thu]
Jesse gave a talk on Reasoning by Cases in Structured Argumentation at the 14th ArgDiap: Formal Models of Reasoning and Argumentation in Poznan.
• [2016-09-06 Tue]
Dunja gave an invited talk on How much should scientific pluralists care about (in)consistency at the Workshop "The Place of Inconsistent Science in Scientific Pluralism" at UNAM in Mexico City.
• [2016-09-01 Thu]
Dunja gave an invited talk on Agent-Based Models of Scientific Inquiry: some problems and some solutions at the Second London Philosophy of Science Graduate Conference Programme, UCL Department of Science and Technology Studies
• [2016-07-26 Tue]
Dunja and Andrea Kruse gave a talk on Can Scientific Rationality be subsumed under Instrumental Rationality at the Cologne Summer School 2016 with Thomas Kelly – Rationality, Objectivity, Disagreement
• [2016-08-22 Mon]–[2016-08-26 Fri]
Mathieu and Christian gave a tutorial on Introduction to Non-Monotonic Logic at ESSLLI 2016. More info
• [2016-07-18 Mon]–[2016-07-21 Thu]
Mathieu and Christian gave a talk on A structured argumentation framework for obligation detachment at DEON 2016 in Bayreuth.
• [2016-05-13 Fri]
We gave a talk introducing our group and research themes we're working on to the other members of the Logical and Methodological Analysis of Scientific Reasoning Processes Research Network (LMASRP, more info here) which is sponsored by the Research Foundation Flanders (FWO).
• [2016-05-09 Mon]
AnneMarie gave a talk on Assumptive hypersequent-based argumentation at PhDs in Logic VIII in Darmstadt.
• [2016-04-25 Mon]
Ofer and Christian gave a presentation on Argumentative Approaches to Reasoning with Maximal Consistency at KR 2016.
• [2016-04-22 Fri]–[2016-04-24 Sun]
Jesse and Christian gave a talk on Relations between assumption-based approaches in nonmonotonic logic and formal argumentation at NMR 2016.
• [2016-03-17 Thu]
Dunja and Christian gave a talk on Scientific Controversies and Interaction Among Scientists at the workshop on "Model(ling) controversies in Science" at the National University of Singapore.
• [2016-01-22 Fri 10:00]–[2016-01-23 Sat 20:00]
Logic Boot Camp 2016
Daniel Skurt, Christian and Jesse organised a two day intensive course for our bachelor and master students.
• [2016-01-09 Sat]–[2016-01-10 Sun]
Dunja and Christian give lectures at the weekend school entitled The Inconsistency of Science at Oxford University on the following topics:

• Christian talks on An Introduction to Paraconsistent Logics
• Dunja talks on Consistency as a methodological standard
• This winter semester Dunja is organising a special module within the optional area of RUB on Conflicting Ideas and Conflicting Interests: Science and Society (Link). In one part of the program guest speakers present insights into conflicts in their respective domains. In the other, practical, part of the program, students have the opportunity to obtain a training in debating.
• [2015-12-17 Thu] Dunja and Christian gave a talk on "Some philosophically relevant considerations in the history of peptic ulcer disease" at the Kolloquium für Wissenschaftstheorie und -geschichte at the Institute for Philosophie I, RUB
• [2015-12-09 Wed]
Christian gave a talk on Detaching Obligations: An Argumentative Approach at ILIAS at the University of Luxembourg

We present a general framework for dealing with the detachment of conditional obligations. Given some facts and conditional obligations, the question whether an unconditional obligation holds is determined by considering reasons for and against its detachment. For this, we use a Dung-style argumentation-theoretical semantics. This part of the talk is joint work with Mathieu Beirlaen (RUB). In the second part of the talk I will present a dynamic proof theory for the system. This part of the talk is based on joint work with Jesse Heyninck (RUB).

• [2015-12-01 Tue] Dunja gave a talk at University of Bayreuth on "Modelling the Division of Cognitive Labor: A Critical Outlook"
• [2015-11-27 Fri] Dunja gave a talk on "Agent Based Models and Interaction Among Scientists – A Critical Look" at the LogiCIC Workshop 2015 "Reasoning in social context", November 26-28, 2015, Amsterdam.
• [2015-11-24 Tue]
Mathieu talked on Deontic logic as structured argumentation at the Venice seminar "Deontic Logic and Ethics"
• [2015-11-10 Tue]
Mathieu and Christian talked on Deontic logic as structured argumentation at the Heinrich-Heine-Universität Düsseldorf.

We present a general framework for dealing with the detachment of conditional obligations. The framework is grounded in an argumentation-theoretical semantics. Detachable obligations are selected in terms of the arguments leading up to them. Whether an obligation is detachable is determined by the attack relations defined among the other obligations in conjunction with a set of facts. Attacks occur when (part of) an argument is conflicted, overridden, or violated by the facts at hand. We show how our proposal adequately handles a wide range of benchmark examples from deontic logic.

• [2015-11-04 Wed 18:00]
Guest talk by Jan Broersen (Utrecht University) at the colloquium of the Institute for Philosophy II. Topic: Semantic choices in modeling responsibility
• [2015-09-28 Mon]
Rune Nyrup (Durham University, Department of Philosophy) gave a talk on Justifying the pursuit of scientific theories: a decision-theoretic perspective
• [2015-09-22 Tue 15:30]
Guest talk by Vlasta Sikimic (University Belgrade). Topic: On expressivity of some structurally “enriched” calculi

Enriching the standard Gentzen calculus with structural connectives and rules may be motivated by philosophical (e.g. unique characterization of logical connectives) or technical reasons (e.g. smoother cut elimination proof). In the talk, we will briefly present some of these reasons and stress the higher expressivity of structurally enriched calculi for capturing a wider array of non-classical logics. We will approach the question of system's expressivity in light of display, higher-level and hypersequent calculi.

• [2015-09-23 Wed]–[2015-09-26 Sat]
Some of us were present at EPSA 2015 in Düsseldorf.

• Mathieu and Bert Leuridan gave a talk on A Logic for the Discovery of Causal Regularities

In the past decades a large number of search algorithms for causal discovery has been developed. Perhaps the most influential theoretical framework for developing such search algorithms is the causal Bayes’ nets framework which has given rise to, among many others, the IC- and IC∗ -algorithms by Pearl (2000, 2009) and the SGS-, the PC- and the IG-algorithms by Spirtes et al. (2000). As is well-known, these algorithms are based on a number of axioms, to wit the Causal Markov Condition and the Faithfulness Condition (which is also known as Stability).1

These conditions or axioms are not absolute. In the words of Spirtes et al. (2000, 9): “The Markov Condition is not given by God; it can fail for various reasons […]. The reliability of inferences based upon the Condition is only guaranteed if substantive assumptions obtain. But the Condition is weak enough that there is often reason to think it applies.”2 One domain in which the Causal Markov Condition fails, comprises deterministic causal structures (Baumgartner, 2009, 72). Such deterministic structures may also violate Faithfulness (Spirtes et al., 2000, 81ff).

In our paper we present a logic, called ELIMr, for the discovery of deterministic causal regularities starting from empirical data. It is an adaptive logic (we shall shortly explain what this means) that is inspired by Mackie’s theory of causes as inus-conditions.

Mackie’s theory of causes as inus-conditions is not probabilistic. It focusses on deterministic causal relations at the generic or type level. From Mill, Mackie borrows the idea that causation is seldom, if ever, an invariable sequence or regularity between a single antecedent (e.g. a short circuit) and a single consequent (e.g. a fire). Instead, it is often the case that the effect P occurs when some conjunction of factors (e.g. ABC; a short circuit, the presence of oxygen, the presence of inflammable materials) occurs, but not when any of these conjuncts fails to occur. Moreover, alternative conjunctions of factors (e.g. the conjunctions DGH and JKL) may also be followed invariably by P. A, in this example, is an insufficient but non-redundant part of an unnecessary but sufficient condition for P. In short, using the first letters of the italicized words, it is an inus-condition for P.

Mackie stresses the fact that our knowledge of complex causal regularities is seldom, if ever, complete. “What we know are certain elliptical or gappy universal propositions.” (Mackie, 1974, 66) Moreover, he writes that “the elliptical character of causal regularities as known is closely connected with our characteristic methods of discovering and establishing them: it is precisely for such gappy statements that we can obtain fairly direct evidence from quite modest ranges of observation.” (Mackie, 1974, 68)

The logic to be presented in this paper will serve as an explication for Mackie’s views on these ‘characteristic methods’. As we will show, the gappy or elliptical character of our causal universal propositions gives the discovery of such propositions an interesting dynamics for which adaptive logics are wellsuited.

Adaptive logics are tools for formalizing defeasible reasoning. They have been used to model a wide variety of reasoning patterns including explanatory reasoning, inductive generalization, and reasoning in the presence of inconsistencies. Moreover, Pearl’s IC-algorithm has served as the basis for ALIC, an adaptive logic for causal discovery (Leuridan, 2009). These patterns are nonmonotonic: conclusions drawn from a set of premises may be withdrawn in the light of additional information (new premises). Adaptive logics are particularly suitable for capturing the non-monotonicity of defeasible reasoning. For a general introduction to adaptive logics, see Batens (2001, 2007).

The logic ELIMr consists of two preliminary logics: ELIr and Mr. ELIr allows to derive logical equivalences — of a particular, Mackie-style type — from empirical data. Mr then serves to minimize these equivalences; intuitively, Mr serves to throw out redundant factors.

During our presentation, we will not spend too much time on the technicalities of our approach. Instead, we will focus on:

1. giving a brief overview of Mackie’s theory of causes as inus-conditions with a special emphasis on the gappy or elliptical nature of our causal knowledge (and corresponding discovery methods);
2. giving a general overview of the preliminary logics ELIr and Mr and the resulting logic for the discovery of causal regularities, ELIMr ;
3. discussing the relation between our logic ELIMr and one recent and very interesting such discovery procedure for deterministic causation that also starts from Mackie’s theory, viz. the Boolean algorithm for coincidence analysis (CNA) proposed by Baumgartner (2009); and
4. discussing the relations between our logic ELIMr and some recent work on qualitative explications of inductive generalization and abductive or explanatory inference, viz. Batens (2011); Beirlaen & Aliseda (2014); Meheus & Batens (2006).

References

• Batens, D. (2001). A general characterization of adaptive logics. Logique & Analyse, 173–175:45–68.
• Batens, D. (2007). A universal logic approach to adaptive logics. Logica Universalis, 1:221–242.
• Batens, D. (2011). Logics for qualitative inductive generalization. Studia Logica, 97:61–80.
• Baumgartner, M. (2009). Uncovering deterministic causal structures: a Boolean approach. Synthese, 170(1):71–96.
• Beirlaen, M. and Aliseda, A. (2014). A conditional logic for abduction. Synthese, 191(15):3733–3758.
• Leuridan, B. (2009). Causal discovery and the problem of ignorance. An adaptive logic approach. Journal of Applied Logic, 7(2):188–205.
• Mackie, J. L. (1974). The Cement of the Universe: A Study of Causation. Clarendon Press, Oxford.
• Meheus, J. and Batens, D. (2006). A formal logic for abductive reasoning. Logic Journal of the IGPL, 14:221–236.
• Pearl, J. (2000). Causality. Models, Reasoning, and Inference. Cambridge University Press, Cambridge.
• Pearl, J. (2009). Causality. Models, Reasoning, and Inference. Cambridge University Press, Cambridge, 2nd edition.
• Spirtes, P., Glymour, C., and Scheines, R. (2000). Causation, Prediction, and Search. MIT Press, Cambridge, Massachusetts.

Footnotes

1 For the Causal Markov Condition, see Spirtes et al. (2000, 54) and Pearl (2000, 30); for the Faithfulness Condition or Stability, see Spirtes et al. (2000, 56) and Pearl (2000, 48) respectively.

2 In this quote they discuss the Markov Condition, but their claim applies to the Causal Markov Condition as well.

• Dunja gave a talk on Is interaction conducive of scientific objectivity

A point often made in the literature on scientific pluralism is that interaction among scientists is a necessary condition for scientific objectivity. This stance has been challenged by Kevin Zollman. In view of a game-theoretic model Zollman has argued that reliable scientific knowledge requires either a restriction of the information flow among scientists or the scientists to have extreme beliefs regarding their pursued hypotheses. In this paper I challenge some basic ideas underlying Zollman’s model by showing that it is based on unwarranted assumptions about how scientists evaluate their hypotheses and how they respond to new evidence.

## Previous Talks

• [2014-09-23 Tue 16:45]
Talk by Dunja and Christian at the Workshop on Norms of Reasoning. Topic: The Normative Role of Evaluative Stances in Scientific Disagreements
• [2014-12-09 Tue 16:00]
Talk by Dunja at the Colloquium for Logic and Epistemology at Ruhr-University Bochum. Topic: Can Scientific Rationality be Subsumed under Instrumental Rationality?
• [2014-12-10 Wed 18:00]
Talk by Christian at the Colloquium of the Institute for Philosophy II, Ruhr-University Bochum. Topic: Sequent-Based Logical Argumentation (co-authored with Ofer Arieli).
• [2015-02-03 Tue 16:00]
Talk by Mathieu at at the Colloquium for Logic and Epistemology at Ruhr-University Bochum. Topic: A Recipe for Safe Detachment.
• [2015-03-09 Mon 16:00]
Invited talk by Dunja at the University of Zurich. Topic: Scientic Disagreements: Epistemological and Methodological Considerations
• [2015-04-02 Thu 14:00]
Jan Potters from Ghent University visited us and presented a talk on
Disputes about Reality: A Practice-Based Approach to Naturalistic Metaphysics and Interpretation in Science.
• [2015-04-14 Tue 17:30]
Talk by all of us at the Celebration of the Institute for Philosophy II at the Ruhr-University Bochum. Topic: Investigating an argumentative approach to defeasible reasoning at the RUB: the Kovalevskaja-workgroup
• [2015-05-07 Thu]
We point your attention to the workshop on Explanation and Abduction: Logico-Philosophical Perspectives organised by our friends at the CLPS at Ghent University. It is the first workshop in a series of workshops on the topic Logic, Reasoning, and Rationality (see http://www.lrr.ugent.be/).
• [2015-05-07 Thu]
Mathieu and Bert give a talk on Discovering Causal Regularities: A Formal Explication.
• [2015-05-14 Thu]
Talk by Jesse at PhDs in Logic VII in Vienna. Topic: Combining Different Forms of Defeasible Reasoning in Abstract Argumentation: Integrating Mechanisms from Adaptive Logics.
• [2015-06-03 Wed 19:00]
Invited talk by Christian at the Institutskolloquium at University Leipzig. Topic: Sequent-Based Logical Argumentation (co-authored with Ofer Arieli)

Defeasible reasoning is indispensable when dealing with a world full of uncertainties: we constantly draw conclusions that we may reject later in view of new information. Examples are numerous: induction, abduction, inferences on the basis of expert opinion, etc. An intuitive perspective on defeasible reasoning is an argumentative one: an inference is retracted if and only if it cannot be defended against counterarguments.

In my talk I will present joint work with Ofer Arieli (Tel Aviv) in which we introduce a general approach for representing and reasoning with argumentation-based systems. In our framework arguments are represented by Gentzen-style sequents, attacks (conflicts) between arguments are represented by sequent elimination rules, and deductions are made according to the skeptical or credulous semantics developed in the tradition of abstract argumentation. This framework accommodates different languages and logics in which arguments may be represented, allows for a flexible and simple way of expressing and identifying arguments, supports a variety of attack relations (including those that reflect relevance or quantitative considerations), and is faithful to standard methods of drawing conclusions by argumentation frameworks.

If time allows, I will also highlight some recent developments in this line of research such as applications in deontic logic and I will show that argumentation theory may benefit from incorporating proof theoretical techniques inspired by the dynamic proofs of adaptive logics.

TITLE
Sequent-Based Logical Argumentation
PRESENTED BY
Christian Straßer
AUTHORS
Christian Straßer and Ofer Arieli
• [2015-06-04 Thu]
Christian gives a talk in a seminar in the master program at University Leipzig on Dynamic Proof Theories as Structured Argumentation.

In this talk I will survey some new developments on the integration of dynamic proofs and structured argumentation. This way I will relate two traditions in the formal modeling of defeasible reasoning: the tradition in formal argumentation and the tradition of adaptive logics.

On the one hand, this concerns work with Ofer Arieli (Tel Aviv) in which we develop dynamic proof theories for sequent-based argumentation. On the other hand, based on work with Jesse Heyninck (Bochum), I show how adaptive logics define a class of structured argumentation frameworks. We translate adaptive logics in the standard format and several generalisations (such as lexicographic, colexicographic adaptive logics, etc.) into the ASPIC-framework or the assumption-based argumentation framework. Finally, if time allows, I will present a new framework of dynamic proofs that are highly expressive, whose retraction mechanism is based on argumentative attacks and that overcomes some limitations of proofs in adaptive logics.

TITLE
Dynamic Proof Theories as Structured Argumentation
PRESENTED BY
Christian Straßer
AUTHORS
this is work in progress based on co-operations with Ofer Arieli (Tel Aviv) and Jesse Heyninck (Bochum)
SLIDES
• [2015-06-08 Mon]
Christian and Jesse give a talk in the Doktorandenkolloquium organised by Tobias Schlicht and Helmut Pulte in which they introduced the Workgroup on Nonmonotonic Logic and Formal Argumentation and the Kovalevskaja Research Project. They also presented some newer developments in argumentative dynamic proof systems.
• [2015-06-10 Wed]–[2015-06-12 Fri]
Talk by Dunja on Is interaction conducive of scientific objectivity? at the 8th Munich-Sydney-Tilburg (MuST) Conference on "Objectivity in Science" at Tilburg University
• [2015-06-18 Thu]–[2015-06-20 Sat]
Talk by Mathieu on A Logic for the Discovery of Causal Regularities (Workhop 'Causal and Probabilistic Reasoning', Munich; with Bert Leuridan)

We present a logic for the discovery of deterministic causal regularities starting from empirical data. Our approach is inspired by Mackie's theory of causes as inus-conditions and makes use of the adaptive logics framework. Our knowledge of deterministic causal regularities is, as Mackie noted, most often gappy or elliptical. The adaptive logics framework is well-suited to explicate both the internal and the external dynamics of the discovery of such gappy regularities. After presenting our logic, we consider some criticisms of the inus-account and how they affect our approach; and we compare our logic with a recent algorithm by Michael Baumgartner.

• [2015-06-22 Mon]–[2015-06-23 Tue]
Some of us will give talks at the workshop Logic - Bochum 1 in Bochum.

• Mathieu presents joint work with Matthieu Fontaine (UNAM, Mexico City) on Inconsistency-Adaptive Dialogical Logic, or How to Dialogue in the Presence of Inconsistencies.

In Batens' inconsistency-adaptive approach, all rules of classical logic are applicable to those parts of our premise set which we can safely consider untainted by inconsistency, without having to specify beforehand which parts of our premises behave consistently.

In order to bring this dynamic approach to paraconsistency closer to our actual argumentative practice, we use its machinery to extend the paraconsistent approach to dialogical logic as developed by Rahman and Carnielli. This way, we obtain a very powerful formalism for the systematic study of dialogues in which two parties exchange arguments over a central claim, in the possible presence of inconsistent information.

TITLE
Inconsistency-Adaptive Dialogical Logic, or How to Dialogue in the Presence of Inconsistencies
AUTHORS
Mathieu Beirlaen and Matthieu Fontaine (UNAM, Mexico City)
WHEN
[2015-06-22 Mon]–[2015-06-23 Tue]
WHERE
Workshop Logic Bochum 1, RUB
• Dunja talks on Concerning Peter Vickers's Recent Treatment of ‘Paraconsistencitis’ (cancelled due to illness)
• Christian and Jesse talk on Dynamic Proof Theories as Structured Argumentation

In this talk we will relate two traditions in the formal modeling of defeasible reasoning: on the one hand the tradition in formal argumentation (1) and on the other hand the tradition of adaptive logics (2,3). We show how adaptive logics define a class of structured argumentation frameworks. We translate adaptive logics in the standard format and several generalisations (such as lexicographic (4), colexicographic adaptive logics, etc.) into the ASPIC-framework (5) or the assumption-based argumentation framework (6). Moreover, we show how stages of adaptive dynamic proofs can be associated with gradually growing attack diagrams. Finally, we define a new family of dynamic proofs that are highly expressive and whose retraction mechanism is based on argumentative attacks.

1. Dung, P. M. (1995). On the acceptability of arguments and its fundamental role in nonmonotonic reasoning, logic programming and n-person games. Artificial Intelligence, 77, 321–358.
2. Batens, D. (2007). A universal logic approach to adaptive logics. Logica Universalis, 1, 221–242.
3. Christian Straßer (2014). Adaptive logic and defeasible reasoning. applications in argumentation, normative reasoning and default reasoning. Springer.
4. Van De Putte, F., Straßer, C. (2013). Three formats of prioritized adaptive logics: a comparative study. Logic Journal of the IGPL, 2(21), 127–159.
5. Prakken, H. (2011). An abstract framework for argumentation with structured arguments. Argument & Computation, 1(2), 93–124.
6. Dung, P., Kowalski, R., & Toni, F. (2009). Assumption-based argumentation. Argumentation in Artificial Intelligence, 199–218.

TITLE
Dynamic Proof Theories as Structured Argumentation
AUTHORS
Christian Straßer and Jesse Heyninck
• [2015-06-25 Thu]–[2015-06-30 Tue]
• [2015-06-25 Thu]–[2015-06-30 Tue]
Talk by Mathieu on A Recipe for Safe Detachment at UNILOG in Istanbul, Turkey.

$$\def\OOs{{\sf O}}$$ $$\def\nc{\mathop{\mid\!\sim}}$$ Let the unconditional obligation $$\OOs B$$ denote It ought to be that $$B$$; and let the conditional obligation $$\OOs(B\mid A)$$ denote If $$A$$, then it ought to be that $B$'. Unconditional obligations $$\OOs B$$ can be rewritten as conditional obligations the condition of which vacuously holds, i.e.\ $$\OOs (B\mid\top)$$.

For $$n\geq 2$$ the following detachment rule permits the derivation of an unconditional obligation from one or more conditional obligations:

$$A_1,\OOs(A_2\mid A_1),\OOs(A_3\mid A_2),\ldots,\OOs(A_n\mid A_{n-1}) \nc \OOs A_n\tag{D}$$

(D) is intended as a rule for safe detachment. That is, an agent deriving a number of unconditional obligations via (D) is meant to be able to jointly fulfill these obligations given the circumstances. Note that applications of the more common rules of factual detachment (from $$A$$ and $$\OOs(B\mid A)$$ to infer $$\OOs B$$) and deontic detachment (from $$\OOs A$$ and $$\OOs(B\mid A)$$ to infer $$\OOs B$$) are special instances of (D). (To see how (D) encompasses the deontic detachment rule, note that the latter is equivalent to from $$\OOs (A\mid\top)$$ and $$\OOs (B\mid A)$$ to infer $\OOs B$'.)

The special turnstile $\nc$' is there to warn the reader that (D) is a defeasible rule. Despite its intuitive appeal, it has been argued that (D) fails in a number of cases, including (but not restricted to) the following:

1. Violations. If the obligation $$\OOs p$$ is violated, i.e.\ if $$\neg p$$ is the case, then we do not want to infer $$\OOs p$$ from $$\OOs (p\mid q)$$ and $$q$$.
2. Specificity cases. Of the two obligations $$\OOs (p\mid q)$$ and $$\OOs (\neg p\mid q\wedge r)$$, the latter is more specific: whereas the former is triggered whenever $$q$$ is the case, the latter is triggered only in the more specific context $$q\wedge r$$. In such more specific contexts, we want to detach only the more specific obligation $$\OOs \neg p$$, and not the less specific obligation $$\OOs p$$.
3. Irresolvable conflicts. Consider the obligations $$\OOs (p\mid q)$$ and $$\OOs (\neg p\mid r)$$, none of which is more specific than the other. Then if both $$q$$ and $$r$$ are the case, we wish to detach neither $$\OOs p$$ nor $$\OOs \neg p$$, since we cannot possibly fulfill both of these obligations.

Although cases like (1.)-(3.) have been well-studied in isolation, what is lacking is a good general account which tells us when exactly it is safe to detach an obligation in the possible presence of violations and conflicting (possibly more specific) obligations. In such a more general setting, a number of new and interesting problems arise, giving rise to different strategies for the defeasible application of (D). Consider, for instance, the set $$\{\neg p,r,s,\OOs(p\wedge q\mid r\wedge s), \OOs(\neg q\mid r)\}$$. The two obligations in this set are in conflict, as we cannot jointly fulfill both. $$\OOs(p\wedge q\mid r\wedge s)$$ is more specific than $$\OOs(\neg q\mid r)$$, but the former obligation is violated in view of $$\neg p$$. Given this set of formulas, one way to proceed is to detach neither of these obligations. A slightly less cautious strategy is to first remove violated obligations, and next to apply (D) in view of the remaining obligations (in the absence of further conflicts). The latter strategy would permit the detachment of $$\OOs \neg q$$, whereas the former would not.

Taking into consideration a wide number of existing and new examples, I present a number of strategies for applying (D) in such a way that all and only unproblematic obligations are detached, so that all detached obligations can be jointly fulfilled by the agent.

• [2015-08-03 Mon]–[2015-08-08 Sat]
We'll all be present at the CLMPS (Congress for Logic, Methodology and Philosophy of Science) in Helsinki. Here's our schedule:

• Mathieu and Christian organize the special colloquium on the Foundations of Defeasible Reasoning. Invited speakers: Niki Pfeifer, Leila Amgoud, and Aldo Antonelli.
• Jesse and Christian give a talk on An assumption-based logic for the analysis of inconsistent premises.

In our talk we present a paraconsistent system based on classical logic. An inspiration comes from the traditional idea in Rescher & Manor (1970) that a necessary condition for being a consequence is to be derivable from a consistent subset of the premises. However, in many applications this criterion is too restrictive because of the resulting syntax-dependency (where different but equivalent formulations of the premise set lead to different conclusions). To overcome this problem our systems are equipped with inference rules that allow for the analysis of the premises. Moreover, unlike traditional systems, consistency assumptions are integrated in a dynamic proof theory. The idea is to protocol significant assumptions about the consistency of formulas that are used in crucial inference steps (such as resolution and aggregation). When these assumptions are violated, the inference gets retracted. This way of integrating consistency assumptions is, for instance, crucial in a predicative setting where no effective test for consistency is available. We will show that depending on what assumptions are protocolled one can obtain either a credulous or skeptical notion of consequence.

We will provide an argumentation-based semantics that is adequate relative to the dynamic proof theory and present meta-theoretic properties of the system. Finally, we compare our logic with similar systems known from the literature such as Quasi-Classical Logic (Besnard & Hunter 2000), the argued consequence (Benferhat et al. 1997), AN(A) (Meheus 2000), CL$$^-$$ (Batens & Provijn 2001), inconsistency-adaptive logics (Batens 2007), and the argumentation systems based on classical logic by Besnard & Hunter (2009).

At the end of the talk we will indicate how by enhancing the system with a non-classical conditional we obtain an interesting variant of default logic.

TITLE
An assumption-based logic for the analysis of inconsistent premises
AUTHORS
Jesse Heyninck and Christian Straßer
• Dunja gives a talk on Can Scientific Rationality be Subsumed under Instrumental Rationality?
• Mathieu gives a talk on Justifying Deductive Inference

There is a tension between the usefulness of deductive inference on the one hand, and its legitimacy on the other. For a deductive inference to be legitimate, the process of recognizing the premises as true must already have accomplished whatever is needed for the recognition of the truth of the conclusion. For a deductive inference to be useful, a recognition of its truth need not actually have been accorded to the conclusion when it was accorded to the premises (M. Dummett, The Justification of Deduction, 1973). Not all inferences we make are deductive: we often reason from true premises to a conclusion that is not guaranteed true. Examples of such ampliative inference patterns include inductive generalization and inference to the best explanation. The power (and use) of ampliative inference lies in its jumping to conclusions. Conclusions reached by these non-deductive methods are not guaranteed true, but they are not completely random either; they are in most cases very likely.

Many ampliative inference patterns permit a deductive reconstruction. For instance, if we know that p entails q and we are looking for an explanation for q, then we may conjecture that p (ampliative (abductive) inference). If p were true, then we obtain the explanandum q by modus ponens (deductive reconstruction). I will argue that, once we acknowledge that inference involves more than mere deduction, we can dissolve the tension between the use and legitimacy of deductive inference as follows. The best way to convince someone of an (ampliative) argument's truth is to present its deductive reconstruction, conjecturing that the premises are true. Deductive logic, then, remains perfectly legitimate, and is useful as a method of exposition because of this legitimacy, i.e. because once we accept the premises are true, we must accept the conclusion.

• [2015-08-31 Mon]–[2015-09-04 Fri]
Tutorial by Christian on Non-monotonic Reasoning as part of the TRS Reasoning School in Natal, Brazil.

Defeasible reasoning is indispensable when dealing with a world full of uncertainties: we constantly draw conclusions that we may reject later in view of new information. For instance, when noticing that the streets are wet, I infer that it has been raining. However, once I discern that the roofs are not wet, I retract my previous inference. In situations like this, we make inferences from premises that do not warrant that our conclusions holds: they only warrant that the a conclusion is sufficiently likely. Defeasible reasoning is not restricted to everyday contexts. It is also abundant in the (pure and applied) sciences and in expert reasoning. E.g., when diagnosing a patient, John, who shows signs that best fit hyperthyroidism, a physician may conclude that John should be tested further for this condition. However, as soon as our physician is informed that John's thyroid has been removed, she will retract her previous inference. As these examples indicate, defeasible reasoning comes in many forms: we reason from effect to cause (abduction), we make generalizations (induction), we reason on the basis of what is normally or typically the case (default reasoning), we infer on grounds of the information our senses give us about our environment, etc. In order to explicate and evaluate such reasoning processes, formal methods were developed: nonmonotonic logics. In this tutorial we will discuss some central approaches in nonmonotonic logic.

TITLE
Tutorial on Non-monotonic Reasoning as part of the TRS Reasoning School in Natal, Brazil
PRESENTED BY
Christian Straßer
WHEN
[2015-08-31 Mon]–[2015-09-04 Fri]
WHERE
Natal, Brazil

## Recent Publications

### 2017

• Jesse Heyninck and Christian Straßer, Revisiting Unrestricted Rebut and Preferences in Structured Argumentation., IJCAI 2017.
• Jesse Heyninck, Peter Verdée and Albrecht Heeffer, Handling Inconsistencies in the Early Calculus An Adaptive Logic for the Design of Chunk and Permeate Structures, Journal of Philosophical Logic (2017). 10.1007/s10992-017-9436-z. link
• Mathieu Beirlaen, Jesse Heyninck, and Christian Straßer, Reasoning by Cases in Structured Argumentation forthcoming in KRR/SAC 2017.
• Ofer Arieli, Annemarie Borg, and Christian Straßer, Argumentative Approaches to Reasoning with Consistent Subsets of Premises in proceedings of IEA/AIE'2017, Lecture Notes in Artificial Intelligence series, Springer
• Annemarie Borg, Daniel Frey, Dunja Seselja and Christian Straßer, An argumentative agent-based model of scientific inquiry, in proceedings of IEA/AIE'2017, Lecture Notes in Artificial Intelligence series, Springer (poster paper)
• Jesse Heyninck, Peter Verdée and Albrecht Heeffer, Handling inconsistencies in the Early Calculus: An Adaptive Logic for the Design of Chunk and Permeate Structures. forthcoming in the Journal of Philosophical Logic

### 2016

• Hans van Ditmarsch, Jan van Eijck, Pere Pardo, Rahim Ramezanian, Epistemic protocols for dynamic gossip, forthcoming in the Journal of Applied Logic, online first
• Mathieu Beirlaen, Jesse Heyninck, and Christian Straßer, Reasoning by Cases in Structured Argumentation forthcoming in KRR/SAC. pdf
• Ofer Arieli and Christian Straßer, Deductive argumentation by enhanced sequent calculi and dynamic derivations, Electronic Notes in Theoretical Computer Science, 323, 21–37 (2016).
• Jesse Heyninck and Christian Straßer, Relations between assumption-based approaches in nonmonotonic logic and formal argumentation, in NMR2016. pdf
• Ofer Arieli and Christian Straßer, Argumentative Approaches to Reasoning with Maximal Consistency in KR16.
• Mathieu Beirlaen and Christian Straßer, A structured argumentation framework for detaching conditional obligations, in DEON 2016
• Mathieu Beirlaen and Matthieu Fontaine, Inconsistency-Adaptive Dialogical Logic, forthcoming in Logica Universalis
• Christian Straßer and Frederik Van de Putte, Proof Theories for superpositions of adaptive logics, forthcoming in Logique et Analyse

### Selected publications, 2014–2015

For a complete list of publications of the members of the group see their respective homepages.

• Realization Theorems for Justification Logics: Full Modularity, Proceedings of Tableaux 2015 (Wroclaw, Poland) by Roman Kuznets and AnneMarie Borg
• Normative Reasoning by Sequent-Based Argumentation in Journal of Logic and Computation (special issue on the DEON 2014 conference), by Christian Straßer and Ofer Arieli
• Nonmonotonic Logic, Stanford Encyclopedia of Philosophy, 2014, by Aldo Antonelli and Christian Straßer.
• Concerning Peter Vickers’ Recent Treatment of ‘Paraconsistencitis’: Review article of Peter Vickers, Understanding Inconsistent Science. Oxford: Oxford University Press, 2014. xii + 273 pp., by Dunja Šešelja and Christian Straßer.
• Ofer Arieli, Christian Straßer, Dynamic Derivations for Sequent-Based Deductive Argumentation, Computational Models of Argument (Ed. S. Parsons, COMMA14) in the series Frontiers in Artificial Intelligence and Applications, IOS Press, pp. 89–100, 2014
• Christian Straßer, Ofer Arieli, Sequent-Based Argumentation for Normative Reasoning, Deontic Logic and Normative Systems (Ed. Fabrizio Cariani, Davide Grossi, Joke Meheus, Xavier Parent) in the series Lecture Notes in Computer Science, Springer, pp. 224–240, 2014
• Christian Straßer, Adaptive Logic and Defeasible Reasoning. Applications in Argumentation, Normative Reasoning and Default Reasoning, Trends in Logic-series on Springer, Volume 38, 2014

## Teaching

### Winter Term 2016 / 2017 @ RUB

• Arguments in Action! Wednesday 16:00–18:00, 18:00–20:00
• Philosophische Logik Tuesdays 12:00–13:30
• Übung zur Philosophischen Logik Tuesdays 14:30–16:00
• Logic: Introductory Course Thursdays 10:00–12:00
• Doktorandenkolloquium (together with Helmut Pulte) Thurdays 14:00–16:00
• Colloquium for Logic and Epistemology (together with Heinrich Wansing) Thursdays 16:00–18:00

### Summer Term 2016 @ RUB

• Prädikatenlogik: Logik II

Dieser Kurs bietet eine Einleitung in die Prädikatenlogik an. Die Sprache der Prädikatenlogik umfasst Quantoren und Prädikate. So ist es möglich, Schlüsse wie den folgenden zu formalisieren:

• Alle Menschen sind sterblich.
• Sokrates ist ein Mensch.
• Folglich ist Sokrates sterblich.

Zunächst wird im Kurs die klassische Prädikatenlogik erster Stufe diskutiert, in der über Individuen quantifiziert wird. Dieses auf Frege, Peirce und Russell zurückgehende System ist das zentrale System der formalen Logik mit Anwendungsbereichen weit über die Philosophie hinaus, etwa die Informatik, die Mathematik, oder die Linguistik. Oft, wenn eindeutige und präzise Definitionen gefordert sind, greifen Wissenschaftler auf die formale Sprache der Prädikatenlogik zurück. Einige der wichtigsten Resultate der formalen Logik wurden im Kontext der Prädikatenlogik erster Stufe erzielt. Manche dieser Resultate, wie die Vollständigkeits- und Unvollständikeitstheoreme von Gödel, oder das Theorem von Löwenheim und Skolem werden im Kurs erklärt und hinsichtlich ihrer philosophischen Relevanz diskutiert.

Neben der Semantik werden Beweissysteme vorgestellt, wie semantische Tableaus und das natürliche Schließen. Die Anwendung dieser Techniken wird in der begleitenden Übungsveranstaltung intensiv geübt.

Je nach Interessenslage der Teilnehmer/innen und sofern Zeit dafür bleibt, bietet sich an, auf etwa folgende weiterführende Themen einzugehen:

• Prädikatenlogik zweiter Stufe, die Quantifizierung über Eigenschaften bzw. Mengen von Individuen zulässt;
• Freie Logik, in der nicht-referierende Terme und leere Diskursdomänen zugelassen sind;
• parakonsistente Prädikatenlogik, in der das Prinzip des Ex Falso Quodlibet aufgegeben wird.

Voraussetzung für den Kurs ist Grundwissen in der Aussagenlogik (etwa die Absolvierung des Grundkurses Logik). Der Kurs soll Studenten/innen ansprechen, die Spass und Interesse an formalen und präzisen Methoden haben.

• Übung zur Prädikatenlogik: Logik II

Namen der Tutoren   Termine   Raum
Dominik Lenze   Di 14-16   GABF 04/511
Kevin Friedrich   Do 16-18   GC 03/46
Jonas Jakubowski   Fr 12-14   GA 03/46
Christian Straßer   Mi 10-12   GA 03/46
Daniel Skurt   Di 16-18   GA 03/46
Jesse Heyninck   Mi 10-12   GA 3/39
• Nonmonotonic logic

Non-monotonic logics aim to capture patterns of defeasible reasoning (DR). DR is indispensable when dealing with a world full of uncertainties: we constantly draw conclusions that we may reject later in view of new information. Moreover, most of human reasoning is defeasible. For instance, when noticing that the streets are wet, I infer that it has been raining. However, once I discern that the roofs are not wet, I retract my previous inference. In situations like this, we make inferences from premises that do not warrant that our conclusion holds: they only warrant that the conclusion is sufficiently likely.

DR is not restricted to everyday contexts. It is also abundant in the (pure and applied) sciences. When observing time after time again that metals, unlike water, do not expand when solidified, it makes sense to accept the generalization that no metal expands when solidified. However, this conclusion had to be rejected once Gallium was discovered. DR is also an indispensable tool in expert reasoning. When hearing about a patient, John, who shows signs that best fit hyperthyroidism, a physician may conclude that John should be tested further for this condition. However, as soon as our physician is informed that John's thyroid has been removed, he will retract his previous inference.

As these examples indicate, DR comes in many forms: we reason from effect to cause (abduction), we make generalizations (induction), we reason on the basis of what is normally or typically the case (default reasoning), we infer on grounds of the information our senses give us about our environment etc. Given that DR is central for human reasoning, this urges us to study DR with exact formal methods. Only in this way are we able to explicate and evaluate reasoning processes in a precise way and to assist and correct people in reasoning.

In this seminar we will cover several important formal accounts of DR including the domains of default reasoning, reasoning on the basis of inconsistent information, abductive reasoning, etc.

The literature for the course will be announced during the first sessions.

Students can get points by giving talks, writings essays, or by means of a written and/or oral test.

• [2016-08-22 Mon]–[2016-08-26 Fri]
Mathieu and Christian will give a tutorial on Introduction to Non-Monotonic Logic at ESSLLI 2016

### Winter Term 2015/ 2016 @ RUB

• Vorlesung: Grundkurs Logik I (Material befindet sich auf Blackboard)

Die Vorlesung "Grundzüge der Logik" bietet eine elementare Einführung in die klassische Aussagen- und Prädikatenlogik. Die Syntax der Aussagen- und Prädikatenlogik wird motiviert und eingeführt. Das Konzept einer modelltheoretischen Semantik wird erörtert und die Wahrheitsbedingungen der klassischen Junktoren und der Quantoren werden erläutert. Ein besonderes Augenmerk wird auf das Problem der Kompositionalität der Bedeutung angesichts variablenbindender Operatoren gelegt. Die Ausdrucksstärke der klassischen Aussagenlogik wird eingehend behandelt. In die Beweistheorie der klassischen Logik wir durch ein System des Baumkalküls eingeführt. Die Begriffe der Korrektheit und Vollständigkeit eines Beweissystems werden erklärt.

The study of logic raises interesting philosophical questions and puzzles about knowledge, meaning, rationality, and reality. Why should we accept an inference as valid? When and how is deduction justified? How do we decide what counts as a logical connective and what does not? Besides classical logic, what are the alternative conceptions of logical inference? What, if anything, does logic tell us about the world out there? This course is intended to familiarize students with these questions by means of a number of classic essays in the field, which are carefully selected in terms of their significance, clarity, and accessibility. Most of the texts will be short and non- technical, although a basic understanding of propositional logic is recommended. The seminar will be taught in English. Below is a preliminary selection of texts to be included in the literature list for this course.

### Other teaching in 2015

• Tutorial on Non-monotonic Reasoning as part of the TRS Reasoning School in Natal, Brazil (Aug 31-Sep 4, 2015).

Defeasible reasoning is indispensable when dealing with a world full of uncertainties: we constantly draw conclusions that we may reject later in view of new information. For instance, when noticing that the streets are wet, I infer that it has been raining. However, once I discern that the roofs are not wet, I retract my previous inference. In situations like this, we make inferences from premises that do not warrant that our conclusions holds: they only warrant that the a conclusion is sufficiently likely. Defeasible reasoning is not restricted to everyday contexts. It is also abundant in the (pure and applied) sciences and in expert reasoning. E.g., when diagnosing a patient, John, who shows signs that best fit hyperthyroidism, a physician may conclude that John should be tested further for this condition. However, as soon as our physician is informed that John's thyroid has been removed, she will retract her previous inference. As these examples indicate, defeasible reasoning comes in many forms: we reason from effect to cause (abduction), we make generalizations (induction), we reason on the basis of what is normally or typically the case (default reasoning), we infer on grounds of the information our senses give us about our environment, etc. In order to explicate and evaluate such reasoning processes, formal methods were developed: nonmonotonic logics. In this tutorial we will discuss some central approaches in nonmonotonic logic.

### Summer Term 2015 @ RUB

Adaptive logics offer a framework for the formal modeling of defeasible reasoning. When we reason defeasibly, our conclusions do not necessarily follow from our premises, but just likely or usually. One of the first applications of adaptive logics was reasoning on the basis of inconsistencies. The usefulness of Classical Logic is limited for this task since it allows one to derive just any formula when confronted with an inconsistent premise set. Inconsistency-adaptive logics, on the other hand, adapt themselves to a premise set in the following sense: they isolate inconsistencies and at the same time allow for the full power of Classical Logic for consistent parts of the premise set. The idea of letting a logic 'adapt itself to the premise set' has since been applied to many other forms of defeasible reasoning such as abductive reasoning (deriving explanations: think of Sherlock Holmes), inductive generalizations (to derive from 'some X are A' that 'all X are A'), normative reasoning in view of conflicting norms ('You shall not kill, but if you do, do it gently.'), default reasoning ('Tweety is a bird, thus she flies.'), and many others. In this seminar we will study adaptive logics, their dynamic proof theory, their semantics, and some of their applications. If time allows we will also investigate links to other central formal frameworks for defeasible reasoning. The literature will be announced in the first meeting. A basic understanding of propositional logic is advisory.

• Normative Reasoning and Deontic Logics, Thursdays, 12-14, GABF 04/609: see here for more information and exercises.

Deontic logic offers a formal explication of reasoning with normative notions such as obligations and permissions. It forms a subclass of modal logic. We start off with standard deontic logic which has the virtue of simplicity. However, it has its limitations. One such limitation concerns normative conflicts (for instance, when you make two promises that you cannot both fulfill), another one concerns conditional norms (for instance, think of a sign which says "Parents are allowed only if accompanied by children"). We will also study several alternative systems that were devised to tackle these problems, such as input/output logic, defeasible deontic logic, default logic, STIT-logic, etc. For the seminar no previous knowledge of modal logic is required though a basic understanding of propositional logic is advisory. Participants have the opportunity to familiarize themselves with central mechanisms in modal logic such as standard Kripkean relational (possible worlds) semantics and generalizations thereof such as neighborhood semantics. The literature will be announced in the first meeting.

• Scientific Pluralism, Tuesdays, 14-16, GABF 04/358

In this seminar we will discuss different conceptions of scientific pluralism proposed in the recent literature, with a special focus on the relation between pluralism and cognitive goals of science, such as scientific objectivity. While a plurality of scientific inquiries in a given domain is often considered fruitful for scientific progress, disagreements among scientists advocating rivaling theories can also pose a threat to scientific objectivity. This motivates the question: which epistemic and methodological norms should guide scientists working in a domain that has a plurality of inquiries and theories? Depending on which cognitive goals and standards are prioritized, this question has been answered in different ways. While some have argued for a critical interaction among disagreeing scientists, others have argued for a restricted information flow between the rivaling camps. Moreover, the role of noncognitive values (such as social, political, ethical or idiosyncratic values) in scientific practice introduces additional problems to normative accounts of scientific pluralism.

Literature:
The exact course material will be provided during the course. The relevant literature includes the following:

• Carrier, M. (2013). Values and objectivity in science: Value-ladenness, pluralism and the epistemic attitude. Science & Education, 22, 2547-2568.
• Chang, H. (2012). Is Water H2O? Evidence, Pluralism and Realism. Springer. Kellert, S. H., Longino, H. E., & Waters, C. K. (Eds.) (2006). Scientific pluralism. Minneapolis: University of Minnesota Press.
• Rolin, K. (2011). Diversity and dissent in the social sciences: The case of organization studies. Philosophy of the Social Sciences, 41 , 470-494.
• Solomon, M. (2006). Groupthink versus the wisdom of crowds: The social epistemology of deliberation and dissent. The Southern Journal of Philosophy, 44
• Zollman, K. J. (2010). The epistemic benefit of transient diversity. Erkenntnis, 72 , 1735.

### Spring Term 2015 @ Ghent University

• Adaptive Logics applied to the Philosophy of Science, block and video sessions by arrangement. The homepage for the course is situated here.
• Discovery and Creativity, block and video sessions by arrangement

### Winter Term 2014/ 2015 @ RUB

• Introducing defeasibility into formal logics: a survey of nonmonotonic logics

Defeasible reasoning is indispensable when dealing with a world full of uncertainties: we constantly draw conclusions that we may reject later in view of new information. Moreover, most of human reasoning is defeasible. For instance, when noticing that the streets are wet, I infer that it has been raining. However, once I discern that the roofs are not wet, I retract my previous inference. In situations like this, we make inferences from premises that do not warrant that our conclusion holds: they only warrant that the conclusion is sufficiently likely. Defeasible reasoning is not restricted to everyday contexts. It is also abundant in the (pure and applied) sciences. When observing time after time again that metals, unlike water, do not expand when solidified, it makes sense to accept the generalization that no metal expands when solidified. However, this conclusion had to be rejected once Gallium was discovered. DR is also an indispensable tool in expert reasoning. When hearing about a patient, John, who shows signs that best fit hyperthyroidism, a physician may conclude that John should be tested further for this condition. However, as soon as our physician is informed that John's thyroid has been removed, he will retract his previous inference. As these examples indicate, DR comes in many forms: we reason from effect to cause (abduction), we make generalizations (induction), we reason on the basis of what is normally or typically the case (default reasoning), we infer on grounds of the information our senses give us about our environment etc. Given that DR is central for human reasoning, this urges us to study DR with exact formal methods. Only in this way, are we able to explicate and evaluate reasoning processes in a precise way and to assist and correct people in reasoning. In this seminar we will cover several important formal accounts of defeasible reasoning including the domains of default reasoning, reasoning on the basis of inconsistent information, abductive reasoning, etc. The literature for the course will be annouced during the first sessions. Students can get points by giving talks, writings essays, or by means of a written and/or oral test.

• Eine Einführung in die formale Argumentationstheorie

In den 1970ern formierte sich eine kritische Bewegung von ArgumentationsTheoretikern/innen bzw. sog. Informalen Logikern/innen. Diese stellten Unzulänglichkeiten der formalen Logik heraus hinsichtlich der Analyse von lebensnahen Argumenten und Schlußweisen jenseits des sterilen Logik-Labors. Ein zentrales Merkmal von vielen Argumenten ist, dass diese auf unterschiedliche Arten kritisierbar sind. Dies zieht nach sich, dass hier die rein deduktive Analyse der klassischen formalen Logik an ihre Grenze stößt, der zufolge die Akzeptierbarkeit der Prämissen die Akzeptierbarkeit der Conclusio (notwendigerweise) nach sich zieht. Neuere Ergebnisse in der formalen Argumentationstheorie und im Bereich der NichtMonotonen Logiken stellen in Aussicht, dass sich die beiden Bereiche der formalen und informalen Logik annähern. Dies ist philosophisch signifikant, da sich damit die Domäne der formal präzisen Methoden erweitert. Entsprechend floriert die formale Argumentationstheorie im Bereich der Künstlichen Intelligenz. Nicht nur ist eine formale Argumentationstheorie nützlich zur Analyse von einem Austausch von Argumenten zwischen mehreren beteiligten Personen. Neueste Einsichten in der Kognitionspsychologie deuten an (und bestätigen damit eine ältere Einsicht Platons), dass ein argumentatives Modell auch angemessen ist zum Verständnis des Schlussfolgerns einer Person im Sinne einer unilateralen Argumentation mit sich selbst. Im Rahmen dieses Seminars werden verschiedene Entwicklungen in der formalen Argumentationstheorie vorgestellt. Credits können erworben werden mit Hausarbeiten und Vorträgen. Die Literatur wird im Seminar bekanntgegeben. Falls Studenten/innen teilnehmen, die nicht flüssig im Deutschen sind, wird das Seminar in Englisch gehalten.

• The Problem of Theory Choice

The problem of theory choice is traditionally considered one of the central problems of philosophy of science and scientific methodology. Answering the question how scientists (are to) choose among a number of rivaling theories is of direct relevance for the way in which we understand scientific rationality. The topic became the subject of heated debates in the twentieth century philosophy of science especially after Kuhn (Kuhn (1962), Kuhn (1977)) had challenged the view that the growth of scientific knowledge is cumulative. While a lot has been written on the criteria underlying theory choice, the idea that scientists choose only one of the rivals, while discarding others as epistemically futile, has been criticized from a pluralist point of view (e.g. Chang (2012)). This poses the question: what does “theory choice” precisely mean when applied to scientific practice? What do scientists exactly choose, to which end do they make such a choice, and in view of which criteria? In this course we will analyze this problem, and discuss the above questions in view of the relevant literature. We will begin by relating the notion of theory choice to the distinction between the context of discovery and the context of justification (Reichenbach (1938)), and to critical analyses of frequent interpretations of this distinction (Nickles (1980), HoyningenHuene (2006)). This will help us to distinguish between different types of theory choice. We will then examine the role of these notions in particular historical case studies. The course material will be provided during the course.

References:

• Chang, H. (2012). Is Water H2O? Evidence, Pluralism and Realism. Springer. Hoyningen-Huene, P. (2006). Context of discovery versus context of justification and Thomas Kuhn. In J. Schickore, & F. Steinle (Eds.), Revisiting Discovery and Justification: Historical and philosophical perspectives on the context distinction (pp. 119–131). Netherlands: Springer.
• Kuhn, T. (1962). Structure of Scientific Revolutions. (3rd ed.). Chicago: The University of Chicago Press.
• Kuhn, T. (1977). The Essential Tension: selected studies in scientific tradition and change. Chicago: University of Chicago press.
• Nickles, T. (1980). Introductory essay: Scientific discovery and the future of philosophy of science. In T. Nickles (Ed.), Scientific Discovery: Case Studies (pp. 1–59). Dordrecht: D. Reidel Publishing Company.
• Reichenbach, H. (1938). Experience and Prediction. An Analysis of the Foundations and the Structure of Knowledge. University of Chicago Press.

## Internal Meetings

We have regular meetings in which members present in a very concise form recent and/or relevant papers. Here's an overview on the papers in the queue.

• In the winter term of 2015 we also had a regular reading group on Gärdenfors Conceptual Spaces (organised by Nina Poth).
• In the summer term of 2015 we had a reading group on disagreements.

## Contact

We are situated at

Ruhr-University Bochum
Universitätsstraße 150
44801 Bochum
Building GA
Office 3/39 (Christian and Dunja)
Office 3/155 (AnneMarie, Jesse, Mathieu, and Pere)
Tel.: +49234-3224721 (office 3/39) and +49234-3228714 (office 3/155)
Email: christian dot strasser at rub dot de

Created: 2017-04-24 Mon 23:34

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