---
bibtex: @InCollection{sep-logic-informal,
author = {Groarke, Leo},
title = {Informal Logic},
booktitle = {The Stanford Encyclopedia of Philosophy},
editor = {Edward N. Zalta},
howpublished = {\url{https://plato.stanford.edu/archives/spr2020/entries/logic-informal/}},
year = {2020},
edition = {Spring 2020},
publisher = {Metaphysics Research Lab, Stanford University}
}
---
Informal logic is the attempt to build a logic suited to ... understand and improve thinking, reasoning, and argument as they occur in real life contexts
Informal logic is usually understood narrowly, as a contemporary field of study which emerged in the last half century, when many philosophers and logicians turned their attention to the analysis, evaluation and improvement of real life argument.
Blair 2015 identifies two key tasks for informal logic: the attempt to develop ways to identify (and “extract”) arguments from natural language discourse and the attempt to develop methods and guidelines for assessing their cogency.
- Sophists on Logos
- Aristotle on Rhetoric & Logic
- The Port Royal Logic (Arnauld & Nicole 1662)
- Elements of Logic and Elements of Rhetoric (Whately 1826, 1830)
- Toulmin’s The Uses of Argument (1958)
- Hamblin’s Fallacies (1970)
- Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life, Kahane 1971
- Little 1980
- Critical Thinking Movement (Siegel 1988)
- Logical Self-Defense (Johnson and Blair 1977)
- Informal Logic
- Argumentation
- Philosophy and Rhetoric
- Argumentation and Advocacy
- Teaching Philosophy
- Inquiry: Critical Thinking Across the Disciplines
- Cogency and Argument and Computation
- ProtoSociology
- Studies in Logic, Grammar, and Rhetoric
Informal logic is “informal” insofar as it studies arguments as they occur in natural language discourse rather than formal languages of the sort that characterize propositional logic, the predicate calculus, modal logic, etc. (languages which have rigorously specified syntax, semantics and grammar, and clearly defined proof procedures).
Within informal logic, the general idea that logic should focus on the logical form of an argument rather than its specific content manifests itself in the common notion that informal logic should assess ordinary arguments by treating them as instances of different argument schemes (schemes that include standard deductive forms of argument like modus ponens, modus tollens and disjunctive syllogism).
- Johnson 1996 ... “dissatisfaction with formal logic as the vehicle for teaching skill in argument evaluation and argument formation” and “A desire to provide a complete theory of reasoning that goes beyond formal deductive and inductive logic.” (p11)
Informal logic understands arguments in the evidentiary sense as collections of premises and conclusions. The premises provide the evidence that supports the conclusion. Hitchcock 2007 defines an argument as “a claim-reason complex” consisting of (1) an act of concluding, (2) one or more acts of premising (which assert propositions in favour of the conclusion), and (3) a stated or implicit inference word that indicates that the conclusion follows from the premises. This makes arguments intentional acts that incorporate (1), (2) and (3).
Hitchcock’s account of argument accommodates ... the possibility that premises and conclusions may be speech acts of different sorts. In particular, it allows a premise to be forwarded by any communication act which asserts a proposition (including, e.g., suggesting, hypothesizing, insulting and boasting); and allows a conclusion to be a request for information (“You were there, so what was it like?”); a request to do something (“The children are shivering, so please close the door.”); a commissive (“I know it matters to you, so I promise to go tomorrow.”), an expressive (“What we did was inexcusable, so we apologize.”) or a declarative (“The evidence shows that you committed an assault, so I find you guilty as charged.”). This broadening of the notion of argument is an essential way to recognize and distinguish the diverse roles that argument and inference actually play in real life contexts.
Arguments need not be language based
Kjeldsen 2015 provides a comprehensive overview of the study of visual arguments – arguments which employ non-verbal visuals (which may include photographs, film, art, cartoons, graphs, diagrams, and architecture)
One might compare the expansion of informal logic to account for such arguments to the attempt to expand formal logic to allow visual deductions (see Barwise and Etchemendy 1998).
As Hitchcock notes, “a poster with a giant photograph of a starving emaciated child and the words ‘make poverty history’ can reasonably be construed as an argument”.
Within informal logic, Gilbert 1997, 2014 (cf. Carozza 2007) was the first to suggest that there are different modes of arguing that need to be distinguished in a theoretical analysis of argument.
Groarke 2015 expands the realm of argument to include, not only visuals, but tastes, smells, musical notes and other non-verbal phenomenon.
EG
On battlefields, for example, doctors have traditionally diagnosed infections using a mode of arguing that can be described as “argument by smell.” In such cases, the scent they smell functions as evidence (as an olfactory premise) for the conclusion that the infection is (or is not) anaerobic.
Extending the notion of argument so that it encompasses different modes of arguing can be done without giving up the evidentiary notion of argument or the idea that evidence is presented in a set of premises that support some conclusion
See also
Gilbert (1997, 2014) develops his account by recognizing argument as it is traditionally conceived as the “logical” mode of argument, and by adding to it “emotional,” intuitive (“kisceral”), and physical (“visceral”) modes of argument. According to this account, a hug, a forlorn look, or tears may count as argument. In real life situations, this underscores the point that they may be a more effective method of resolving disagreement than premises as they have been traditionally conceived.
- identifying the various parts of an argument.
As Blair 2015 has emphasized, the ultimate goal of informal logic is normative. Its aim is an account of argument that can be used to decide when arguments are strong and weak; good and bad; and plausible and implausible.
the strength of an argument is a function of two things: (i) the viability of its premises, and (ii) the strength of the inference from these premises to its conclusion.
The simplest criteria for this is AV (Acceptability & [informal] Validity)
Following Johnson & Blair (1977, 1994) is ARS (Acceptability, Relevance, Sufficiency)
The premises of an argument count as relevant to its conclusion when they provide some support for the conclusion and sufficient when they provide enough support to establish it as plausible.
Because real life arguing tends to take place in contexts characterized by uncertainty which make it difficult to make judgments of truth or falsity .... Informal logic favors acceptability over truth as a criteria for judging premises for other reasons as well.
NLD is another approach ...
Govier (1987) “Natural Language Deductivism” (NLD) ... maintains that all informal arguments can best be interpreted as attempts to create deductively valid inferences, and should be analyzed and assessed accordingly.
In general, a deductive conclusion is as certain as the premises it is founded on.
In dealing with arguments which are not explicitly deductive, the NLD approach interprets an argument as a deductive argument by attributing it implicit premises that make it so.
Because NLD reconstructs informal arguments as deductively valid arguments, Govier describes it as a theory of “reconstructive” deductivism. It makes argument assessment a two step process which (i) reconstructs an argument (by adding implicit premises) to make it a clearly deductive inference, and (ii) then evaluates the argument by assessing the strength of its (explicit and implicit) premises.
Argument Schemes describe common patterns of reasoning (both justified and fallicious)
Walton, Reed & Macagno 2008 provide a significant compendium of 96 schemes.
One way to understand schemes is as moves in argument which are backed by the warrants implied by the critical questions that accompany them.
Groarke & Tindale 2013 use traditional fallacies as a basis for a set of schemes, treating ad hominem, guilt by association, appeals to ignorance, two wrongs reasoning, etc. not as fallacies, but as legitimate patterns of reasoning. .... On this account of schemes, fallacies turn out to be deviations from an inherently correct norm.
Dove 2016 has discussed the application of argument schemes to cases of visual argument, showing how this is easily accomplished. He suggests one scheme, “argument from fit” as a uniquely visual scheme that applies to arguments in which the borders of two objects are visually inspected to determine whether the objects are part of a larger whole