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Informal logic (or, occasionally, non-formal logic) is the study of arguments as presented in ordinary language, as contrasted with the presentations of arguments in an artificial, formal, or technical language (see formal logic). It quickly became affiliated with the Thinking Skills Movement[1] and especially with critical thinking (see below). Later still it became affiliated with the interdisciplinary inquiry known as Argumentation theory.
The precise nature and definition of informal logic are matters of some dispute. Ralph H. Johnson and J. Anthony Blair define informal logic as "a branch of logic whose task is to develop non-formal standards, criteria, procedures for the analysis, interpretation, evaluation, criticism and construction of argumentation in everyday discourse."[2] This definition reflects what had been implicit their practice and what others[3][4][5] were doing in their informal logic texts.
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To appreciate this switch in focus from formal to informal logic, one must set aside stock examples such as: "All men are mortal, Socrates is man, therefore Socrates is mortal." This is not the sort of matter people choose to argue about in their everyday lives; there is nothing to argue about, since the conclusion necessarily follows from the premises. (It is a paradigm of a certain kind of reasoning, called a syllogism). In the wider world, people argue about which party should form the government, how to deal with global warming, the morality of capital punishment, or the effects of television, subjects that do not lead to answers that have only a single "truth", or "falseness", as do statements within formal logic. In informal logic, argument is distinguished from implication and entailment, argument being construed as activity or discourse in which reasons are given to persuade rationally.
The following is an example of such an argument.
| “ | Senator Paul Martin was well known for extolling the virtues of his hometown of Windsor, Ontario (Canada). On this occasion, Senator Martin rose to defend Windsor against a slur contained in Arthur Hailey's novel about the auto industry, Wheels. Hailey wrote of "grimy Windsor" across the border from Detroit, "matching in ugliness the worst of its U.S. senior partner." According to press reports, Martin responded: "When I read this I was incensed ... Those of us who live there know that (Windsor) is not a grimy city. It is a city that has one of the best flower parks in Canada. It is a city of fine schools, hard working and tolerant people." | ” |
Martin is defending the claim that Windsor is not grimy by offering his reasons. But the conclusion has to be extricated from the text; and Martin makes no claim about the strength of his argument, which is typical. His argument makes use of assumptions that need to be unearthed—as is also typical of arguments as they occur in daily life. And there are problems of interpretation, i.e. what he meant by "grimy." This example is typical of the sorts of argument dealt with by informal logic and presents a contrast with the Socrates example. In (2000), Johnson and Blair modified their definition, and broadened the focus now to include the sorts of argument that occurs not just in everyday discourse but also disciplined inquiry—what Weinstein (1990) calls "stylized discourse." The following is Anselm’s ontological argument—an attempt to persuade the receiver of the truth of the proposition that God exists.
| “ | We have the concept of a being than which no greater can be conceived. Such a being must exist, for if such a being fails to exist, then a greater being — namely, a being than which no greater can be conceived, and which exists — can be conceived. But this would be absurd: nothing can be greater than a being than which no greater can be conceived. So a being than which no greater can be conceived — i.e., God — exists.[6] | ” |
To understand this definition above, one must understand "informal" which takes its meaning in contrast to its counterpart "formal." (This point was not made for a very long time, hence the nature of informal logic remained opaque, even to those involved in it, for a period of time.) Here it is helpful to have recourse to Barth and Krabbe (1982:14f) where they distinguish three senses of the term "form." By "form1," Barth and Krabbe mean the sense of the term which derives from the Platonic idea of form—the ultimate metaphysical unit. Barth and Krabbe claim that most traditional logic is formal in this sense. That is, syllogistic logic is a logic of terms where the terms could naturally be understood as place-holders for Platonic (or Aristotelian) forms. In this first sense of "form," almost all logic is informal (not-formal). Understanding informal logic this way would be much too broad to be useful.
By "form2," Barth and Krabbe mean the form of sentences and statements as these are understood in modern systems of logic. Here validity is the focus: if the premises are true, the conclusion must then also be true also. Now validity has to do with the logical form of the statement that makes up the argument. In this sense of "formal," most modern and contemporary logic is "formal." That is, such logics canonize the notion of logical form, and the notion of validity plays the central normative role. In this second sense of form, informal logic is not-formal, because it abandons the notion of logical form as the key to understanding the structure of arguments, and likewise retires validity as normative for the purposes of the evaluation of argument. It seems to many that validity is too stringent a requirement, that there are good arguments in which the conclusion is supported by the premises even though it does not follow necessarily from them (as validity requires). An argument in which the conclusion is thought to be "beyond reasonable doubt, given the premises" is sufficient in law to cause a person to be sentenced to death, even though it does not meet the standard of logical validity.
By "form3," Barth and Krabbe mean to refer to "procedures which are somehow regulated or regimented, which take place according to some set of rules." Barth and Krabbe say that "we do not defend formality3 of all kinds and under all circumstances." Rather "we defend the thesis that verbal dialectics must have a certain form (i.e., must proceed according to certain rules) in order that one can speak of the discussion as being won or lost" (19). In this third sense of "form", informal logic can be formal, for there is nothing in the informal logic enterprise that stands opposed to the idea that argumentative discourse should be subject to norms, i.e., subject to rules, criteria, standards or procedures. Informal logic does present standards for the evaluation of argument, procedures for detecting missing premises etc.
Some dissent from the view that informal logic is not a branch or subdiscipline of logic.[7][8][9] Massey criticizes the study on the grounds that it has no theory underpinning it. Informal logic, he says, requires detailed classification schemes to organize it, whereas in other disciplines the underlying theory would provides this structure. He maintains that there is no method of establishing the invalidity of an argument aside from the formal method, and that the study of fallacies may be of more interest to other disciplines, like psychology, than to philosophy and logic.[7]
Logic is the normative study of reasoning (q.v.). Wherever there is reasoning, there is a logic that seeks to articulate the norms for that type of reasoning. Informal logic differs from formal logic not only in its methodology but also by its focal point. That is, the social, communicative practice of argumentation can and should be distinguished from implication (or entailment)—a relationship between propositions—which is the proper subject of formal deductive logic; and from inference—a mental activity typically thought of as the drawing of a conclusion from premises. Informal logic may thus be said to be a logic of argument/ation, as distinguished from implication/inference.[10]
Since the 1980s, informal logic has been partnered, in the minds of many, with critical thinking and indeed some seem to equate the two. Still, it is clear that they are different, though related. Critical thinking is, in the first instance, a kind of activity, or mental practice, whereas informal logic is a kind of inquiry or theory. Critical thinking also designates an educational ideal that emerged with great force in the 80s in North America as part of an ongoing critique of education as regards the thinking skills not being taught. The precise definition of "critical thinking" is a subject of much dispute[11] but there is agreement that in order to think critically one must be able to process arguments. That is where informal logic comes into play. Critical thinking, according to Johnson, is the evaluation of an intellectual product (an argument, an explanation, a theory) in terms of its strengths and weaknesses.[11] While much of critical thinking will focus on arguments (because one has to grapple with reasons for and reasons against) and hence require skills of argumentation, critical thinking requires additional abilities not supplied by informal logic: the ability to obtain and assess information, to clarify meaning. Also many believe that critical thinking requires certain dispositions.[12] Many succumb to the temptation to conflate critical thinking with problem solving. Johnson takes these issues to be part of the Network Problem[13] and to require, for their proper settlement, a theory of reasoning.
"Argument" is not the same as "argumentation" but scholars do not agree on just how these terms should be used. In the approach taken here, argumentation refers to a social and cultural practice whose chief components are the process of arguing and the product—the argument—which may emerge from that process. But, Pragma-dialecticians, for example, use "argumentation" where many would use "argument".[14] Argumentation theory (or the theory of argumentation) has come to be the term that designates the theoretical study of argumentation. This study is interdisciplinary in the sense that no one discipline will be able to provide a complete account understanding. A full appreciation of argumentation requires insights from logic (both formal and informal), rhetoric, communication theory, linguistics, psychology, and, increasingly, computer science. Since 1970s, there has been significant agreement that there are three basic approaches to argumentation theory: the logical, the rhetorical and the dialectical. According to Wenzel,[15] the logical approach deals with the product, the dialectical with the process, and the rhetorical with the procedure. Thus, informal logic is one contributor to this inquiry, being most especially concerned with the norms of argument.