Douglas N. Walton

Canadian academic and author (1942–2020)

A special issue of the journal Informal Logic surveyed Walton's contributions to informal logic and argumentation theory up to 2006.

Walton earned his PhD from the University of Toronto in 1972.

Walton's work represents a distinctive approach built around a set of practical methods to help a user identify, analyze, and evaluate arguments in specialized areas such as law and science, as well as arguments of the kind used in everyday conversational discourse. Walton has called this approach logical argumentation, and as a method it has twelve defining characteristics, shown below in a simplified list. The method analyzes and evaluates argumentation concerning a contestable claim, one where there is evidence for the claim as well as against it. The claim is tested evidentially by the pro and con arguments that support or attack it. The procedure for examining and criticizing the arguments on both sides forms a dialogue structure in which two sides, the claimant and its opponent, take turns putting forward speech acts (for example, asking questions and putting forward arguments). The dialogue has rules for incurring and retracting commitments that are activated by speech acts. For example, when a participant makes an assertion (claim), he or she becomes committed to the proposition contained in the assertion. The method uses the notion of commitment (acceptance) as the fundamental tool for the analysis and evaluation of argumentation rather than the notion of belief. The reason is that belief is held to be a psychological notion internal to an agent that can only be determined indirectly, by inference to the best explanation of the agent's speech and actions. The method assumes a database of commonly accepted knowledge that, along with other commitments, provides premises for arguments. The knowledge base is set in place at the opening stage, but can be revised as new relevant information comes in. The method comprises the study of explanations as well as arguments, including the form of argument called inference to the best explanation or abductive reasoning. The dialogue system is dynamic, meaning that it continually updates its database as new information comes in that is relevant to an argument being considered. The arguments advanced are (for the most part) defeasible, meaning that they are subject to defeat as new relevant evidence comes in that refutes the argument. Conclusions are accepted on a presumptive basis, meaning that in the absence of evidence sufficient to defeat it, a claim that is the conclusion of an argument can be tentatively accepted, even though it may be subject to later defeat. The dialogue uses critical questioning as a way of testing plausible explanations and finding weak points in an argument that raise doubt concerning the acceptability of the argument. The method uses standards of proof. Criteria for acceptance are held to depend on standards that require the removal of specifiable degrees of reasonable doubt. The method is based on argumentation schemes, such as argument from expert opinion, that represent commonly used types of arguments that are defeasible. In the method, schemes work as heuristic devices that only offer presumptive support of a claim that may have to be withdrawn as new evidence comes in. The schemes connect arguments together into sequences, often called chaining, by taking the conclusion of one argument as a premise in a subsequent argument. Some common schemes are argument from goal based reasoning, argument from negative consequences, argument from positive consequences, inference to the best explanation (abductive reasoning), argument from sign, argument from analogy, argument from precedent, argument from an established rule, argument from evidence to a hypothesis, argument from cause to effect, argument from correlation to cause, argument from sunk costs, argument from threat, argument from perception, argument from witness testimony, argument from expert opinion, argument from ignorance, argument from commitment, direct ad hominem argument, argument from inconsistency of commitments, slippery slope argument.