Doug Walton, who died in January 2020, was a prolific author whose work in informal logic and argumentation had a profound influence on Artificial Intelligence, including Artificial Intelligence and Law. He was also very interested in interdisciplinary work, and a frequent and generous collaborator. In this paper seven leading researchers in AI and Law, all past programme chairs of the International Conference on AI and Law who have worked with him, describe his influence on their work.

: This paper is about the nature of practical reasons. More specifically, my primary goal is to explore when an agent has a justifying reason for action¾that is, a reason that can be used for justifying an action that has been done or that the agent is planning to do. This concept of reason is central to ethics and to practical philosophy in general. I defend an account of reason according to which a piece of practical reasoning gives an agent (...) a reason for action if he has a reason for its premises and a warrant for holding that these premises logically support the conclusion. That is roughly to say that justifying reasons are closed under logical entailment. To achieve this aim, I shall discuss the components of such reasons. Section 2 presents a principle of closure for justifying reasons and clarifies two important clauses of this principle. In the last section, I show how my account can sidestep the regress problem in practical reasoning. (shrink)

This article offers an analysis of normative practical reasoning. Reasoning of this type includes at least one normative belief and it has a practical conclusion (roughly, a conclusion about what to do). The principal question I am interested in is whether this type of practical reasoning can be logically conclusive. This issue has received remarkably little philosophical discussion despite the central role this reasoning plays in our everyday discourse about action and in the resolution of ethical problems. I distinguish three (...) kinds of normative reasons. Quasi -normative reasoning, I maintain in Section 1, can only be valid if it is in fact theoretical reasoning, despite appearance to the contrary. In Section 2, I argue that there are two kinds of genuine normative reasoning (purely normative reasoning and hybrid reasoning) that can be logically conclusive. This article also shows that practical arguments are non-trivially ambiguous (which has been largely ignored in the literature) because they can at the same time express different pieces of practical reasoning that have a different logical status. (shrink)

Since Aristotle it has been common among philosophers to distinguish between two fundamental types of reasoning, theoretical and practical. We do not only want to work out what is the case but also what we ought to do. This article offers a logical analysis of instrumental reasoning, which is the paradigm of practical reasoning. In the first section I discuss the major types of instrumental reasoning and show why the accounts of most authors are defective. On the basis of this (...) discussion, I demonstrate in the second section that different types of normative conclusions are derivable from instrumental arguments and I show that it is an argument’s logical structure that determines what type of conclusion this is. (shrink)