Informal logic studies the identification, analysis, evaluation, criticism and construction of arguments. An argument is a set of one or more interlinked premiss-illative-conclusion sequences. Premisses are assertives, not necessarily asserted by anyone. Conclusions can be assertives, directives, declaratives, commissives or expressives. Each can be expressed either in language or by visual images or physically. Two arguments can be linked either by having a conclusion of one as a premiss of the other or by having one as a premiss of the other. A box-arrow system for diagramming arguments thus conceived is illustrated with reference to three expressed arguments; the diagrams show that the diagramming system can handle conditional proof, argument about an arbitrary instance as a proof of a universal generalization, argument by cases, and reductio ad absurdum. A final section lists issues in informal logic and gives some indication of the range of positions taken on these issues.
Hitchcock, D. (2017). Informal Logic and the Concept of Argument. In Argumentation Library (Vol. 30, pp. 447–475). Springer Nature. https://doi.org/10.1007/978-3-319-53562-3_29