Argument between Form and Content

Abstract

Cogency is the central normative concept of contemporary informal logic: argument is good when acceptable (A) and relevant (R) premises provide sufficient (S) grounds for the conclusion. In classical formal logic, inference is necessarily truth-preserving: if the premises are true, so is the conclusion because of the logical form of the sentences involved. We get broad logical form when some (or all) repeated content expressions are replaced with variables. The conclusion follows in a broad sense if a schematic universal conditional – whose antecedent is the conjunction of the argument’s premises and whose consequent is the argument’s conclusion – is acceptable (I employ David Hitchcock's approach to material consequence). The conditional claims that it is not possible (in some narrower and defeasible sense) that premises are acceptable and the conclusion is not. The broad consequence captures the RSA criterion: patterns of broad logical form preserve acceptability, and the sufficiency of premises guarantees that the connection between premises and the conclusion is modally stable (in a certain defeasible and qualified way). The so-called “informal” logic based on the RSA criterion is nevertheless logic even if the broad consequence differs from classical logical consequence and deductive validity.