The investigation of computational models of argument is a rich, interdisciplinary, and fascinating research field with two ultimate aims. A theoretical goal is to understand argumentation as a cognitive phenomenon by modelling it in computer programmes, while a practical goal is to support the development of computer-based systems able to engage in argumentation-related activities with human users or among themselves. These ambitious research goals involve the study of natural, artificial, and theoretical argumentation and, as such, requires openness to interactions with a variety of disciplines, such as philosophy, cognitive science, linguistics, communication studies, formal logic, game theory and mathematical graph theory.

The computational study of argumentation has two main historic origins. In 1987 John Pollock published his seminal paper Defeasible reasoning, in which he stressed the importance of reasons in the construction of arguments and gave the first systematic formal account of the evaluation of arguments given their internal structure and their relation with counterarguments. And in 1995 Phan Minh Dung’s paper On the acceptability of arguments and its fundamental role in nonmonotonic reasoning, logic programming and n-person games initiated the study of so-called abstract argumentation frameworks, which leave the nature of arguments and their relations unspecified but still allow for a rich theory of argument evaluation. This paper was in 2018 awarded the AI Journal Classic Paper Award, to recognise its role in making argumentation a mainstream research topic in artificial intelligence.

Since 2006 the biennial International Conference on Computational Models of Argument (COMMA) has provided a dedicated forum for presentation and discussion of the latest advancements in this interdisciplinary field, covering both basic research and innovative applications. The first COMMA was supported by the EU 6th Framework Programme project ASPIC and was hosted by the University of Liverpool in 2006. After the event, a steering committee promoting the continuation of the conference was established and, since then, the steady growth of interest in computational argumentation research worldwide has gone hand in hand with the development of the conference itself and of related activities by its community. Since the second edition, organized by IRIT in Toulouse in 2008, plenary invited talks by world-leading researchers and a software demonstration session became an integral part of the conference programme. The third edition, organized in 2010 by the University of Brescia in Desenzano del Garda, saw the addition of a best student paper award. The same year, the new journal Argument and Computation, closely related to the COMMA community, was started. Since the fourth edition, organized by the Vienna University of Technology in 2012, an Innovative Application Track and a section for Demonstration Abstracts were included in the proceedings. At the fifth edition, co-organized in 2014 by the Universities of Aberdeen and Dundee in Pitlochry, the main conference was preceded by the first Summer School on Argumentation: Computational and Linguistic Perspectives. The same year also saw the launch of the first International Competition on Computational Models of Argumentation (ICCMA). Since COMMA 2016, hosted by the University of Potsdam, the COMMA proceedings are Open Access. This COMMA was also the first that included additional satellite workshops in the programme. COMMA 2018 was hosted by the Institute of Philosophy and Sociology of the Polish National Academy of Sciences in Warsaw, Poland. It included an industry afternoon bringing together businesses, NGOs, academics and students interested in practical applications of argument technologies in industry.

This year COMMA is in Italy for the second time, now hosted by the University of Perugia. It is preceded by the 4th Summer School on Argumentation: Computational and Linguistic Perspectives (SSA 2020), and features a demonstrations session and three satellite workshops. The International Workshops on Systems and Algorithms for Formal Argumentation (SAFA), initiated at COMMA 2016, has its third edition, while there is a new Workshop on Argument Visualization. Finally, the well-known Workshop on Computational Models of Natural Argument, established in 2001, has its 20th edition at COMMA 2020.

Despite these continuing traditions, COMMA 2020 is different from all preceding COMMAs in one respect: because of the coronavirus pandemic that hit the world early 2020, the entire conference and its preceding summer school have to take place online. This is, of course, a huge disappointment for the local organisers and for all participants, who had been looking forward to a great conference in the beautiful city of Perugia. Nevertheless, going online secures the continuation of the COMMA conference series, allowing the presentation and discussion of the latest research results and their publication in these proceedings.

The COMMA 2020 programme reflects the interdisciplinary nature of the field, and its contributions range from theoretical to practical (although most are theoretical). Theoretical contributions include new formal models, the study of formal or computational properties of models, designs for implemented systems and experimental research. Practical papers include applications to medicine, law, crime investigation, chatbots and online product reviews. The conference respects its historic origins by providing both abstract and structured accounts of argumentation. Some papers propose formal argument schemes for specific forms of argument. Many papers focus on the evaluation of arguments or their conclusions given a body of arguments, with a continuation of a recent trend to study gradual (e.g. probabilistic) notions of evaluation. Other papers focus on the dialogical processes by which argumentation proceeds, sometimes from a game-theoretical point of view. The focus on argument mining, which first appeared at COMMA 2016, is continued while an emerging trend this year is the use of argumentation for explainable AI.

The three invited talks also reflect the diverse nature of the field. Professor Catarina Dutilh Novaes from the Free University Amsterdam discusses the role of adversariality in argumentation from a social-epistemology perspective. Professor John Horty of the University of Maryland gives a logical analysis of defeasible reasoning about open-textured predicates in natural language and legal theory. Finally, Professor Chris Reed of the University of Dundee covers a broad spectrum from philosophical foundations via algorithmic research to technological applications.

Finally, we acknowledge the work of all those who have contributed in making the conference and its satellite events a success. We would like to thank IOS Press for publishing these proceedings and continuing to make them Open Access. As local and international sponsors of the conference, we would like to thank in random order Fondazione Cassa di Risparmio di Perugia, Gruppo Nazionale per il Calcolo Scientifico (GNCS-INdAM), the Artificial Intelligence Journal (funding scheme for promoting AI research), the Department of Mathematics and Computer Science (University of Perugia), the University of Perugia, Confcommercio Umbria, Associazione Nazionale Imprese ICT (Assintel), and iter innovazione terziario. We also thank the Italian Association for Artificial Intelligence (AIxIA), which supported the best student paper award. We thank the invited speakers Catarina Dutilh Novaes, John Horty and Chris Reed for their insightful and inspiring talks. We acknowledge steady support and encouragement by the COMMA Steering Committee, and are very grateful to the Programme Committee and additional reviewers, whose invaluable expertise and efforts have led to the selection of 28 full papers and 13 short papers out of a record total of 78 submissions, and 13 demonstration abstracts. The submission and reviewing process has been managed through the Easychair conference system, which we acknowledge for supporting COMMA since the first edition. Our thanks also to the COMMA 2020 workshop organisers Jodi Schneider, Matthias Thimm, Fabian Sperrle and their co-organisers, and to the summer school programme chair Massimiliano Giacomin. Last but not least, we thank all the authors and participants for contributing to the success of the conference with their hard work and commitment.

Henry Prakken (Programme chair)

Stefano Bistarelli (Conference chair)

Francesco Santini (Conference co-chair and demo chair)

Carlo Taticchi (Publicity chair)

Utrecht/Perugia, July 2020