Douglas Neil (Doug) Walton, a Canadian philosopher, was born in Hamilton, Ontario, on June 2, 1942; he died in Windsor, Ontario, on January 3, 2020. He contributed extensively and influentially to the field of informal logic and the theory of argumentation. His work inspired many by its broad and deep coverage of key themes in the field, such as the nature and classification of fallacies, of argumentation schemes, and of dialogue types. Any attempt by us to detail the various themes and subjects studied and shaped by Walton is bound to be incomplete because of the sheer abundance of his publications: We counted thus far 519 publications (62 books—among them 44 monographs, 275 journal articles, 59 contributions to books, 56 contributions to conference proceedings, and 67 reviews). In all of his works he combined a philosophical, logical, and theoretical point of view with a keen interest in real world practices and occurrences, expressing his insights in a down-to-earth way, and illustrating them by many attractive examples and case studies.

Walton studied at the University of Waterloo (1962–1964), where he was a teaching fellow in philosophy (1963–1964) and received his bachelor’s degree with honors in 1964. He was granted permission to enter a PhD program at the University of Toronto without having taken a master’s degree. There he held a Province of Ontario fellowship (1964–1967) and a Canada Council doctoral fellowship (1967–1969), as well as the positions of tutor at Victoria College (1965–1967), junior fellow at Massey College (1967–1968), and instructor at Scarborough College (1967–1968). In 1972, he received a doctorate from the University of Toronto after having completed a PhD thesis entitled The Meaning of ‘Can’: A Study in the Philosophy of Language (supervisor was John Woods; advisers were Barron Brainerd, Hans G. Herzberger, and Jordan Howard Sobel).

Earlier, in 1969, Walton had taken up a position as lecturer at the University of Winnipeg, where he became assistant professor in 1971, associate professor in 1976, and full professor in 1982, the position he held until his retirement in 2008. From 1977 until 1986 he also held a chair as adjunct professor at the faculty of graduate studies of the University of Manitoba. After his retirement from the University of Winnipeg, Walton moved to the University of Windsor (Ontario) to take up the posts of Assumption University Chair in Argumentation Studies (until 2013) and Distinguished Research Fellow at the Center for Research in Reasoning, Argumentation, and Rhetoric (CRRAR). From 2012 to his untimely death in 2020, he was also adjunct professor in the Department of Philosophy of the University of Windsor.

Walton was a much-respected scholar who received many grants, fellowships, and awards. We mention some of these: In 1987, he received the prestigious Killam Research Fellowship; in 1988 the Erica and Arnold Rogers Award for Excellence in Scholarship and Research; in 1990 he was the winner at the first presentation of an ISSA Award, a prize awarded by the International Society for the Study of Argumentation for outstanding scholarship in the field of argumentation studies; in 1991 he received a grant from the Social Sciences and Humanities Research Council of Canada, the first of several such grants; in 1995 a discretionary grant from the University of Winnipeg, followed up by more such grants; in 1998 he received a J. William Fulbright Foreign Scholarship; in 2009, at the University of Windsor, he received the Faculty of Arts and Social Sciences Dean’s Special Recognition Award for excellence in research, scholarly activity, and creativity. Among his fellowships abroad, we mention two research stays in New Zealand (University of Wellington, 1975–1976, University of Auckland 1983), two periods as fellow-in-residence at the Netherlands Institute for Advanced Study in the Humanities and Social Sciences (NIAS, 1987 and 1989–1990), stays as research associate at the University of Western Australia (1996) and at the Oregon Humanities Center (1997), and as a Fulbright senior fellow at Northwestern University (1999), visiting professorships at the University of Arizona (2001) and at the University of Lugano, Switzerland (2007, 2009), and a Ferdinand Braudel fellowship at the European University Institute at Florence, Italy (2011).

The scope of Walton’s national and international activities and contacts in the field of argumentation studies surfacing from this list is confirmed by an even longer list of his participations in various scholarly committees, such as program committees for conferences and editorial boards. To these one must add his educational activities, which included, besides the writing of textbooks, the teaching of numerous courses at various levels, in Canada and abroad, as well as the supervision or examination of many PhD students in a number of different countries. Some of these PhD students later became his co-authors of articles and books. But Walton’s greatest drive was for research and writing.

Walton’s first publication dates from 1971: “The Modal Auxiliary Verb ‘Can’,” published in the Proceedings of the Linguistic Circle of Manitoba and North Dakota. At that time, he was, one might say, at square one but he was not going to stay there for long. The next year, he and John Woods published a paper ‘On Fallacies,’ which prepared the stage for a series of publications that would later be referred to as the Woods-Walton Approach to the study of fallacies (see the papers assembled in Woods and Walton 1989 and also their textbook Argument: The Logic of the Fallacies, 1982). In these papers Woods and Walton, inspired by Hamblin (1970), diligently studied many of the traditional fallacies, making ample use of various then recent formal developments in philosophical logic. They did not aim to present a unified account of the fallacies, but showed for each case separately how formal methods could be profitable.

While these papers on fallacies show that Walton was early in his career as an author already much involved with the study of argumentation, there were also other themes he wrote about. We saw that his first publication, as well as his PhD dissertation, was concerned with the semantics of modal terms, and there were to follow more papers on the philosophy of logic and language, but also on other philosophical subjects, such as action theory, free will and determinism, omnipotence, death, and (medical) ethics. After having published two co-edited volumes, one on action theory and one on omnipotence, the first book he authored appeared in 1979: On Defining Death, followed the next year by Brain Death: Ethical Considerations. Two other books, both on medical ethics, followed soon: Ethics of Withdrawal of Life-Support Systems: Case Studies on Decision-Making in Intensive Care (1983) and Physician–Patient Decision-Making: A Study in Medical Ethics (1985). In 1986, he published another book in moral philosophy: Courage: A Philosophical Investigation. By that time Walton had already started a series of monographs within the field of argumentation theory of which the first was Topical Relevance in Argumentation (1982). Many more books on argumentation were yet to follow: Among colleagues, it was said that “while we all try to write papers, Doug writes books.”

One theme of primary importance in all of Walton’s work is the study of argumentation in contexts of dialogue. This was naturally connected with an interest in dialogue games as studied by formal dialectic. Walton’s increasing interest in formal dialectic, which was already present in the Woods-Walton papers, came particularly to the fore in a monograph devoted to the role of dialogue games in the study of fallacies: Logical Dialogue-Games and Fallacies (1984) and in his editing of, and contributing to, a special issue of Synthese (63 (3), 1985) entitled ‘The Logic of Dialogue’. In 1987 he started, with Erik Krabbe, to work on a project on the role of commitment in dialogues, in which the two developed a typology of dialogues consisting of six main types (published in Walton and Krabbe, Commitment in Dialogue: Basic Concepts of Interpersonal reasoning, 1995). Fallacies were associated with illicit shifts from one type to another. Walton used this typology and variants of it in many of his books and wrote extensively about each type of dialogue in The New Dialectic: Conversational Contexts of Argument (1998).

Walton’s interest in contexts of dialogue was matched by an interest in the pragmatics of argumentation. It is therefore not surprising that he noticed and appreciated the work of the Dutch pragma-dialecticians. Especially at and after the first ISSA conference in Amsterdam (1986), they had a fruitful intellectual relationship. Walton was obviously influenced by many pragma-dialectic points of view. The pragma-dialecticians read and discussed Walton’s work noticing that he was getting close to them, but not yet there…

Guided by these interests in dialectics and pragmatics, Walton diligently devoted monographs to many of the core subjects of argumentation theory. In 1996, for instance he published a book on argumentation schemes and one on argument structures (Argumentation Schemes for Presumptive Reasoning, and Argument structure: A pragmatic Theory). By the way, in the same year he published two more books and seven papers.

On fallacy theory, he not only wrote a monograph (A Pragmatic Theory of Fallacy, 1995) but also a great number of books each of which focused on patterns of argument connected with a particular type of fallacy. The first of these was Arguer’s Position: A Pragmatic Study of Ad Hominem Attack, Criticism, Refutation, and Fallacy (1985), the last one, written with Fabrizio Macagno, Interpreting Straw Man Argumentation (2017). In these books it is time after time shown how patterns of argument that are traditionally judged fallacious can have non-fallacious uses. Each use of such a pattern needs to be carefully analyzed and evaluated in the particular context in which it occurs. Consequently, Walton illustrated his books by numerous interesting case studies. Walton’s fallacy books constitute by themselves an impressive oeuvre. Yet some of his most influential books are to be found elsewhere.

Judging by his citations as collected on Google Scholar,Footnote 1 Walton’s most influential publications (some of which were already mentioned above) are, besides Commitment in Dialogue (with Erik Krabbe, 1995), the two books he wrote about argumentation schemes (Argumentation Schemes for Presumptive Reasoning, 1996, and Argumentation Schemes, with Chris Reed and Fabrizio Macagno, 2008), Informal Logic: A Handbook for Critical Argument (1989), and The New Dialectic: Conversational Contexts of Argument (1998). And indeed these belong to his most guiding works, exposing his ideas on the, not necessarily formal, but always systematic study of argumentative patterns as they can be observed in actual contexts and dialogues. In these books we meet with the typology of dialogues, the use of argumentation schemes with critical questions, and the potential of informal logic, all of them central and influential themes in Walton’s research.

A bit lower on the list, but still highly cited (250 +), we see books on the study of fallacies (A Pragmatic Theory of Fallacy, 1995, which we mentioned before, and Ad Hominem Arguments, 1998) and on specific forms of reasoning (Appeal to Expert Opinion: Arguments from Authority, 1997, Abductive Reasoning, 2004, Plausible Argument in Everyday Conversation, 1992). All publications in the top 20 are books, except one, which is a journal paper: `The Carneades Model of Argument and Burden of Proof’, published in Artificial Intelligence 171 (2007), co-written with Tom Gordon and Henry Prakken. The Carneades model contains a theory of argumentation, of critical questions, and of burden of proof, provided with computer support and a diagram format. The high ranking of this paper provides a good example of how Walton’s work was picked up not only in the humanities, but also in computer science and artificial intelligence.

Walton was a collaborative scholar. It is true that he wrote most of his monographs all by himself but also that many of his publications were the result of a joint effort. He had a keen interest in the views of his colleagues in the field of argumentation studies, which also extended to approaches by researchers in other disciplines and actually, in daily life, to what he could learn from people working in all kinds of craft or trade.

Throughout his career Walton had a taste for interdisciplinary research. This bent for interdisciplinary cooperation can be nicely exemplified by his invited lecture at the International Conference on Formal and Applied Practical Reasoning (FAPR 1996, Bonn). There he explained to a crowd of researchers in artificial intelligence, philosophy, psychology, linguistics, software engineering, intelligent systems, and industrial applications (see the blurb of the conference proceedings) how important it is to study logic in an applied form, with an eye for the pragmatic, situated, communicative context of reasoning. He also spoke of the opportunities provided by software developed in order to support critical thinking and argumentation, a topic that he later engaged in extensively (for instance in collaboration with Chris Reed and Tom Gordon, both present at that conference). In the (extensive but imperfect) lists we consulted of titles of his books and papers, we found a first occurrence of terms like `computer science’ and `computational’ in the year 2000 (`The Place of Dialogue Theory in Logic, Computer Science and Communication Studies’ Synthese 123 (3)) and the last occurrence as late as 2019 (`How Computational Tools Can Help Rhetoric and Informal Logic with Argument Invention’ with Thomas Gordon, Argumentation 33 (2)). In the meantime, Walton published many papers in the interdisciplinary journal Argument & Computation. His paper `Using Argumentation Schemes to Find Motives and Intentions of a Rational Agent’ appeared posthumously in Argument & Computation 10 (3). He had submitted corrections to the proofs some days before he died.

Early in this long interdisciplinary involvement with computation, Walton was one of the participants of the Bonskeid House Symposium on Argument and Computation (Pitlochry, Scotland, 2000), where a group of researchers interested in the philosophical and/or computational study of argument gathered, on invitation by Chris Reed and Tim Norman. The week’s aim was not so much to present and discuss papers as to produce, on the spot, a book on the topic, which must have been right up Walton’s alley. At the symposium, Walton and others briefly presented their ideas from which much interaction ensued between the quite different approaches of philosophy and computer science. Food was awful, but an outline was planned, work divided, and drafts of chapters were produced in small groups. There was also time to climb Ben Vrackie and to visit a distillery. The book indeed appeared, be it a few years later (Argumentation Machines: New Frontiers in Argument and Computation, Chris Reed and Tim Norman (Eds.), 2003).

Walton’s extensive efforts into bridging philosophy and computer science gained him much appreciation in the field of computational argumentation, as may be for instance apparent from his contributing to the 2009 handbook Argumentation in Artificial Intelligence (edited by Iyad Rahwan and Guillermo Simari), for which he wrote the first chapter `Argumentation Theory: A Very Short Introduction’.

Walton, who wrote a book about legal argumentation (Legal Argumentation and Evidence, 2002), became also involved in the interdisciplinary field of Artificial Intelligence and Law, where philosophical, computational, and legal insights are combined. Because of the prominence of argumentation and dialogue in the practice of legal problem solving and conflict resolution, Walton’s methods found much resonance. Walton, in turn, was inspired by the tools and examples of this interdisciplinary field. One example is the application of argumentation schemes and their critical questions in the context of legal evidence, which Walton developed together with Floris Bex, Henry Prakken and Chris Reed (‘Towards a Formal Account of Reasoning about Evidence: Argumentation Schemes and Generalisations’ Artificial Intelligence and Law 11 (2–3), 2003). Another is the already mentioned work on Carneades. Walton also developed case studies, such as on the Popov v Hayashi court case about the ownership of a valuable baseball (in a Salomon-like judgment, the California court, ruled that the ball had to be sold, and its value split) (‘A Carneades Reconstruction of Popov v Hayashi’ with Thomas Gordon, Artificial Intelligence and Law 20 (1), 2012). Walton collected his contributions in the books Argumentation Methods for Artificial Intelligence in Law (2005) and Witness Testimony Evidence: Argumentation, Artificial Intelligence and Law (2008).

Doug Walton will be remembered by his friends and colleagues, not only as the erudite and influential scholar and prolific author he certainly was but foremost as the friendly and cooperative man, with a subtle, often unnoticed, dry sense of humor, who shared so much of his intellectual wealth with us. Doug was survived by his wife Karen Walton, née Jacklyn, known by many in the research community as her husband’s dedicated companion on numerous national and international academic trips. They had been together for 52 years.