Informal logic, intuitively, refers to the principles of logic and
logical thought outside of a formal setting. However, perhaps because
of the "informal" in the title, the precise definition of "informal
logic" is a matter 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." This definition reflects what had been implicit in
their practice and what others were doing in their informal logic
Informal logic is associated with (informal) fallacies, critical
thinking, the thinking skills movement and the interdisciplinary
inquiry known as argumentation theory.
Frans H. van Eemeren writes
that the label "informal logic" covers a "collection of normative
approaches to the study of reasoning in ordinary language that remain
closer to the practice of argumentation than formal logic."
2 Proposed definitions
4 Relation to critical thinking
5 Relation to argumentation theory
6 See also
Special journal issue
9 External links
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Informal logic as a distinguished enterprise under this name emerged
roughly in the late 1970s as a sub-field of philosophy. The naming of
the field was preceded by the appearance of a number of textbooks that
rejected the symbolic approach to logic on pedagogical grounds as
inappropriate and unhelpful for introductory textbooks on logic for a
general audience, for example Howard Kahane's
Logic and Contemporary
Rhetoric, subtitled "The Use of
Reason in Everyday Life", first
published in 1971. Kahane's textbook was described on the notice of
his death in the Proceedings And Addresses of the American
Philosophical Association (2002) as "a text in informal logic, [that]
was intended to enable students to cope with the misleading rhetoric
one frequently finds in the media and in political discourse. It was
organized around a discussion of fallacies, and was meant to be a
practical instrument for dealing with the problems of everyday life.
[It has] ... gone through many editions; [it is] ... still in print;
and the thousands upon thousands of students who have taken courses in
which his text [was] ... used can thank Howard for contributing to
their ability to dissect arguments and avoid the deceptions of
deceitful rhetoric. He tried to put into practice the ideal of
discourse that aims at truth rather than merely at persuasion.
(Hausman et al. 2002)" Other textbooks from the era taking this
approach were Michael Scriven's Reasoning (Edgepress, 1976) and
Logical Self-Defense by Ralph Johnson and J. Anthony Blair, first
published in 1977. Earlier precursors in this tradition can be
considered Monroe Beardsley's Practical
Logic (1950) and Stephen
Toulmin's The Uses of
The field perhaps became recognized under its current name with the
First International Symposium on Informal
Logic held in 1978. Although
initially motivated by a new pedagogical approach to undergraduate
logic textbooks, the scope of the field was basically defined by a
list of 13 problems and issues which Blair and Johnson included as an
appendix to their keynote address at this symposium:
the theory of logical criticism
the theory of argument
the theory of fallacy
the fallacy approach vs. the critical thinking approach
the viability of the inductive/deductive dichotomy
the ethics of argumentation and logical criticism
the problem of assumptions and missing premises
the problem of context
methods of extracting arguments from context
methods of displaying arguments
the problem of pedagogy
the nature, division and scope of informal logic
the relationship of informal logic to other inquiries
David Hitchcock argues that the naming of the field was unfortunate,
and that philosophy of argument would have been more appropriate. He
argues that more undergraduate students in North America study
informal logic than any other branch of philosophy, but that as of
2003 informal logic (or philosophy of argument) was not recognized as
separate sub-field by the World Congress of Philosophy. Frans H.
van Eemeren wrote that "informal logic" is mainly an approach to
argumentation advanced by a group of US and Canadian philosophers and
largely based on the previous works of
Stephen Toulmin and to a lesser
extent those of Chaïm Perelman.
Alongside the symposia, since 1983 the journal Informal
Logic has been
the publication of record of the field, with Blair and Johnson as
initial editors, with the editorial board now including two other
colleagues from the University of Windsor—
Christopher Tindale and
Hans V. Hansen. Other journals that regularly publish articles on
informal logic include
Argumentation (founded in 1986),
Argumentation and Advocacy (the journal of the American
Forensic Association), and Inquiry: Critical Thinking Across the
Disciplines (founded in 1988).
Johnson and Blair (2000) proposed the following definition: "Informal
logic designates that branch of logic whose task is to develop
non-formal2 standards, criteria, procedures for the analysis,
interpretation, evaluation, critique and construction of argumentation
in everyday discourse." Their meaning of non-formal2 is taken from
Barth and Krabbe (1982), which is explained below.
To understand the 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. 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. This type of argument, based on
accumulation of evidence rather than pure deduction, is called a
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.
Johnson and Blair (2000) noticed a limitation of their own definition,
particularly with respect to "everyday discourse", which could
indicate that it does not seek to understand specialized,
domain-specific arguments made in natural languages. Consequently,
they have argued that the crucial divide is between arguments made in
formal languages and those made in natural languages.
Fisher and Scriven (1997) proposed a more encompassing definition,
seeing informal logic as "the discipline which studies the practice of
critical thinking and provides its intellectual spine". By "critical
thinking" they understand "skilled and active interpretation and
evaluation of observations and communications, information and
Some hold the view that informal logic is not a branch or
subdiscipline of logic, or even the view that there cannot be such a
thing as informal logic. Massey criticizes informal logic
on the grounds that it has no theory underpinning it. Informal logic,
he says, requires detailed classification schemes to organize it,
which in other disciplines is provided by the underlying theory. 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.
Relation to critical thinking
See also: Critical thinking
Since the 1980s, informal logic has been partnered and even
equated, in the minds of many, with critical thinking. The precise
definition of "critical thinking" is a subject of much dispute.
Critical thinking, as defined by Johnson, is the evaluation of an
intellectual product (an argument, an explanation, a theory) in terms
of its strengths and weaknesses. While critical thinking will
include evaluation of arguments and hence require skills of
argumentation including informal logic, critical thinking requires
additional abilities not supplied by informal logic, such as the
ability to obtain and assess information and to clarify meaning. Also,
many believe that critical thinking requires certain dispositions.
Understood in this way, "critical thinking" is a broad term for the
attitudes and skills that are involved in analyzing and evaluating
arguments. The critical thinking movement promotes critical thinking
as an educational ideal. The movement 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.
Relation to argumentation theory
The social, communicative practice of argumentation can and should be
distinguished from implication (or entailment)—a relationship
between propositions; 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 argumentation, as
distinguished from implication and inference.
Argumentation theory is interdisciplinary in the sense that no one
discipline will be able to provide a complete account. A full
appreciation of argumentation requires insights from logic (both
formal and informal), rhetoric, communication theory, linguistics,
psychology, and, increasingly, computer science. Since the 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, 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.
Informal inferential reasoning
Philosophy of language
^ See Johnson 1999 for a survey of definitions.
^ Johnson, Ralph H., and Blair, J. Anthony (1987), "The Current State
of Informal Logic", Informal Logic, 9(2–3), 147–151. Johnson &
Blair added "... in everyday discourse" but in (2000), 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
^ Resnick, 1989
^ a b
Frans H. van Eemeren (2009). "The Study of Argumentation". In
Andrea A. Lunsford; Kirt H. Wilson; Rosa A. Eberly. The SAGE handbook
of rhetorical studies. SAGE. p. 117.
^ a b c d David Hitchcock,
Informal logic 25 years later in Informal
Logic at 25: Proceedings of the Windsor Conference (OSSA 2003)
^ JSTOR 3218569
^ Fisher (2004) p. vii
J. Anthony Blair and Ralph H. Johnson (eds.), Informal Logic: The
First International Symposium, 3-28. Pt. Reyes, CA: Edgepress
^ Johnson and Blair (2000), p. 100
^ As Johnson (1999) does.
^ Johnson and Blair (2000), p. 95
^ a b Massey, 1981
^ Woods, 1980
^ Woods, 2000
^ Johnson (2000) takes the conflation to be part of the Network
Problem and holds that settling the issue will require a theory of
^ a b Johnson, 1992
^ Ennis, 1987
^ Johnson, 1999
^ Wenzel (1990)
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Johnson, R. H. & Blair, J. A. (2000). Informal logic: An overview.
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Woods, J. (2000). How Philosophical is Informal Logic? Informal Logic
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