Nature of Fallacy:
Formal and Informal Fallacies in Argumentation
Abstract: A fallacy is a mistake in reasoning: an argument which
either does not prove, or does not provide evidence for, its conclusion.
The history, nature, and classification of informal and formal fallacies is
defined, characterized, and discussed.
- Main Approaches to Argumentation Studies
- The Standard Treatment of Informal Fallacies
- Some Difficulties with the Standard Treatment of Informal Fallacies
- What is a Fallacy?
- Paralogisms, Sophisms, and Paradoxes
- Three Basic Types of Fallacies: Informal,
Deductive, and Inductive:
- Chart of Fallacies
- Final Comments and Cautions on Fallacies
- Readings on Fallacies
Main Approaches to Argumentation Studies
Apart from formal deductive logic and inductive logic, the main
approaches for the study of argumentation include these overlapping
fields which are perspectives by which arguments can be viewed:
(1) informal logic (including critical thinking), (2) dialectical logic (including
pragma-dialectical discourse analysis and pragmatic argumentation theory), and (3)
rhetoric (including debate and persuasion).
- Informal Logic is the normative study of natural
language arguments (as opposed to the formal or abstract
methods of deductive logic) which seeks to develop standards
of use and methods of evaluation of ordinary language
Some informal arguments can be properly translated into
formal logic. Formal logic uses symbolism and formal methods
to evaluate arguments as valid or not; whereas, informal
arguments not translatable into formal deductive or inductive
arguments can be evaluated as evidentially relevant and
sufficient if they are “good” arguments. Researchers
disagree on the place of informal logic with respect to
formal logic and argumentation theory. The Canadian school
of informal logic, for example, holds that the study emphasizes
arguments in everyday discourse not analyzable by formal
logic. Informal logic is seen in these notes as the examination of
the justification of arguments in context rather examination of the
persuasiveness of arguments.
Critical thinking differs from informal logic in that
this educational reform movement emphasizes the study of various
intellectual activities for problem solving in accordance with
rational criteria, whereas informal logic is narrower
in focus and emphasizes traditional argument interpretation
and evaluation of argumentative everyday language, dialogue, and
J. Anthony Blair and Ralph H. Johnson point out, informal
logic aspires to be a theory-based subject; whereas, critical
thinking is an activity utilizing informal logic and other
methods of problem solving. These other
methods include creative thinking, inquiry, information
processing, and reasoning within different subject matters.
- Dialectical Logic approaches argumentation as shared
argumentative discourse between or among participants with
opposing points of view. Pragma-dialectical discourse sets rules
for rational critical discussion, and the speech acts which
violate these rules are viewed as fallacies. In this manner,
fallacies are viewed as statements that impair the progress of
the dialogue. Pragmatic logical
argumentation evaluates defeasible normative reasoning within
a dialectical context by means of argumentation schemes, mappings,
and appropriate contextual standards of proof. Often dialectical
arguments are responses to oppositional counter-arguments. Dialectical
logic is viewed here as a study of the persuasiveness of arguments
rather that a study of the justification of arguments. Dialectical
logic intends consensus as a surrogate for truth.
- Rhetoric emphasizes the effectiveness of emotive significance and argument used
for the persuasion of changing attitudes toward a standpoint or
point of view. Often the arguments are shaped to appeal to the
attitudinal outlook of a specific audience such that truth per
se is not specifically sought. Rhetoric can still be evaluated
in terms of formal logic, but, for example, Chaïm Perelman
and Lucie Olbrecht-Tyteca, emphasize rhetoric's purpose in terms
of the effects of audience value preferences. Although rhetoric
is eschewed by some formal logicians, the cornerstone of the
rhetorical approach is that emotively neutral logical arguments,
by themselves, rarely influence audience opinion. As a form of
nonanalytic thinking, value-judgment hierarchies replace reason
- These lecture notes emphasize informal and formal logic.
Ordinary language arguments will often be translated with the principle of charity into
conventional deductive and inductive arguments. Currently,
most researchers in the argumentation field seem to agree with
F. H. van Eemeren's appraisal:
“[T]he 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.”
- Some researchers maintain accurate translation of many
natural language arguments into formal logic is not possible
given their vagueness, ambiguity, and incompleteness. Thus,
it is thought, on this view, formal logic is not useful
for these kinds of argumentation since a neutral observer's
objective point of view is not possible. However, if adequate
clarification of what is stated is not possible, then it is
doubtful that reliable understanding of what is stated in
argumentation is possible outside of interpretation or
- G.C. Goddu has argued that informal logic cannot meaningfully
be defined in terms of the logic of real arguments, i.e.
the logic of natural or ordinary everyday arguments, since there
is no clear demarcation between real arguments and other kinds
In this regard, Gottlob Frege writes:
”Of course we have to be able to count on a meeting
of minds, on others’ guessing what we have in mind. But all
this precedes the construction of a system and does not
belong within a system. In constructing a system it must be
assumed that the words have precise meanings and that we
know what they are.”
For communication to be possible for all statements, a regulative
principle is implicitly adopted that a sentence which states
something can be translated into a different statement or statements
which recognizably express the same thought.
The Standard Treatment of Fallacies
The traditional or standard treatment of informal fallacies is
currently developing along divergent lines of inquiry.
- In 1970 C.L. Hamlin pointed out that the standard treatment
of fallacies remained much the same as the thirteen fallacies
pointed out by Aristotle in his Sophistical Refutations.
Hamlin decries the standard treatment:
“[I]n most cases, I think it should be admitted, is
as debased, worn-out and as dogmatic a treatment as could
be imagined — incredibly tradition-bound, yet lacking
in logic and historical sense alike, and almost without
connection to anything else in modern logic at
And Douglas Walton cautions:
“Indeed, it has been shown that many of the so-called
‘fallacies’ are, in some instances, not incorrect
arguments at all, but reasonable kinds of argument or reasonable
kinds of criticisms of arguments.”
Currently, defeasible reasoning
and informal fallacies are analyzed in accordance with argumentation
schemes and pragmatic theories of dialogue. Moreover, on many occasions,
some supposed “traditional informal fallacies” can be set
out and explained as acceptable (inductive) arguments.
- Many traditionally-defined informal fallacies such as ad
hominem, ad verecundiam, tu quoque,
ad ignorantiam, slippery slope, composition, division,
and others can be contextually effective and legitimate arguments when the
conclusion follows from the premises with some degree of probability.
- For example, the basis of ad hominem argument
depends on the relevance of the relationship between what is said
and the character of the person who said it. Reliable authorities
are more likely to state good arguments concerning their field
of expertise than are non-authorities in that field. The relevance
of a disputant's personal information must be established on a
case-by-case basis. Obvious specialized expertise provides inductive
evidential relevance for rendering conclusions drawn in that field
more reasonable. In general, weak arguments can be distinguished
from a fallacious argument.
- Decades ago, F.H. van Eemeren and R. Grootendorst pointed out:
“Referring to mitigating circumstances which make a
fallacy no fallacy after all, however, does not solve anything.
… [T]he detection and identification of fallacies
becomes very much ad hoc: Each case has to be examined
on its own merits … an adequate theory of fallacies is
then out of the question.
The claim that some informal fallacies are not fallacies on occasion
appears to be simply a verbal statement rather than a factual
statement. E.g. the “mitigating circumstance”
distinguishing between a fallacious ad hominem
argument and a credible ad hominem is the
essential aspect of the definition of the fallacy: viz., the
relevance or the irrelevance of the disputant's
character with respect to what the disputant states.
- Mistakes in arguments present in monotonic
logic disputes are not limited to the errors of invalidity
and unsoundness, but, also errors can arise from improbability of
the inference based on the meaning of, or semantic content in,
the statements used.
- The legitimacy of informal logic as a separate discipline is
grounded on the presupposition that not all instances of ordinary
language reasoning can be accurately translated into the abstract
formal structures of deductive or inductive logic. The conclusions
of those arguments can be altered by new information.
- If this is the case, the possibility of informal logic as an
independent logical theory may well be based on the rejection of Sir
William Hamilton's logical postulate as he applied it to formal
“The only postulate of Logic which requires an articulate
enouncement is the demand, that before dealing with a judgment or
reasoning expressed in language, the import of its terms should be
fully understood; in other words, Logic postulates to be allowed to
state explicitly in language all that is implicitly contain in the
Some argumentation theorists today seem to disagree with this thesis.
For them, the early Ludwig Wittgenstein's optimistic statement …
“Everything that can be thought at all can be
thought clearly. Everything that can be said can be said
does not take account of the tacit vagueness, ambiguity, and
inexplicitness, as noted above.
- J. Anthony Blair summarizes the popular current view as to why informal
logic is not reducible to formal logic:
“The idea that arguments can be adequately analyzed
and evaluated outside the contexts or situations of their
use is more or less dead among all but the most isolated
philosophers and logicians.”
Even so, there still remain logicians who see the need for
formal-reconstruction in the interpretation of much or all of informal
- Some logicians, e.g., Peter Ramus, , Francis
among others, did not assay the treatment of informal fallacies
because they emphasized that logic is concerned with correct
reasoning. Some current logic textbooks in do not cover the
topic of informal fallacies.
Yet, unless we are aware of some of the mistakes that are
likely to be made, i.e., unless we know how to avoid
typical mistakes in thinking, we are unlikely reason well.
Some Difficulties with the Standard Treatment
No one is particularly satisfied with the traditional treatments
of fallacies — many fallacies cannot be categorically
- Thus, it may well be impossible to give a systematic treatment
of fallacies, in part because different methods of logic have
been adopted and in part because the nature of errors in reasoning
are not always due to grammatical structures and forms of
- Augustus De Morgan writes in his Formal Logic:
“There is no such thing as classification of
the ways men arrive at an error: it is much to be doubted
whether there ever can be.”
- H.W.B. Joseph says in his Introduction to Logic:
“Truth may have its norm, but error is infinite in its
aberrations, and they cannot be digested in any classification.
The same inconclusive argument may often be referred at will
to this or that head of fallacies.”
- As an example of a fallacy which may be identified in either
of two ways, consider the fallacy of the ambiguous middle term in syllogistic logic,
also termed the four term fallacy,
and normally described as a formal fallacy. The same
argument can also be identified as a fallacy of equivocation
which is an informal fallacy. Augustus De Morgan
provides this example of a four term fallacy with equivocation
of the term “criminal action”:
“All criminal actions ought to be punished by law.
The form of this fallacy is illustrated as:
Prosecutions for theft are criminal actions.
Therefore prosecutions for theft ought to be punished by
All CA is PL
Although the terms for CA and CA’ appear to
be the same, they have different meanings. The first occurrence
of the phrase “criminal action” refers to “the
commission of a crime” and the second refers to a “legal
proceeding.” Either fallacy, formal or informal, can be
cited as the reason the argument is fallacious depending on whether
the structure of the argument or the content of the argument is
All PT are CA’
All PT are PL
- No unified theory of fallacy has been proposed, except in
an exceedingly superficial manner by negative definition.
I.e., a fallacy is said to be incorrect reasoning. This
negative definition of course depends upon having a complete
and consistent explication of the meaning of proper reasoning.
- However, most logicians do not consider just any
error in reasoning a fallacy per se; the term
“fallacy” is reserved by many logicians for
recognizable errors of a specific kind. Even so, some accounts
of informal fallacies are cluttered with countless minor
variations of traditional fallacies.
- Specific informal fallacies often are not definable in terms
of some specific or common trait but are instead characterized
by various family resemblances. For this reason, the completion of
the development of a standard taxonomy of informal fallacies is
- So, most likely, what we call ‘fallacy’ has no
common single meaning, and the characterization of the uses of
this word fits Ludwig Wittgenstein's notion of “family
resemblance” — where “we see a complicated
network of similarities overlapping and criss-crossing; sometimes
overall similarities, sometimes similarities of
- Francis Bacon wrote in a similar regard:
But these small wares and petty points of cunning are infinite;
and it were a good deed to make a list of them, for that
nothing doth more hurt in a state than that cunning mean pass for
But most fallacies and related infelicities of persuasion occurring
in everyday discourse overlap so much in their complexities that
attempting to name as many as possible proves unprofitable.
- Even though there exists no agreed upon theory of fallacy, informal
fallacies in this course are more or less organized traditionally. An
attempt is made to incorporate the standard treatment of fallacies with
a practical view toward everyday reasoning.
What is a Fallacy?
- Historically, fallacies have been defined in many different
ways, not all of which are consistent with the usages in contemporary
logic. Following Richard Whately, the first English logician to
base the subject of fallacies on logical principles by dividing
fallacies into logical or formal and material, many logicians
define “fallacy” as some form of deceptive reasoning.
Richard Whately writes:
“By a ‘Fallacy’ is commonly meant
‘any deceptive argument or apparent-argument, whereby
a man is himself convinced, — or endeavors to convince others
— of something which is not really proved.’”[emphasis
And Jeremy Bentham writes:
By the name fallacy it is common to designate any argument
employed, or topic suggested, for the purpose, or with a probability,
of producing the effect of deception …
Indeed, the conventional definition of “fallacy” expressed
in the Oxford English Dictionary is “A deceptive or
misleading argument, a sophism.”
- The traditional view of fallacy, closely related to this
view, is the oft-used contemporary definition: “an
argument which seems to be valid, but really is not.” However,
several serious problems with this definition for logic are
- The definition is psychological; it turns on whether
an individual happens to be misled by an argument. William
Spalding points out deception is not essential to the
definition of fallacy:
“The name is sometimes … used to deceive.
But the intention is a point of secondary
importance in the theory of fallacies …
- What could count as something being unqualifiedly
“deceptive”? E.g. consider this oft-used
fallacy of equivocation in several 18th century books:
Nothing is better than Heaven;
Since few persons would regard the argument as valid, on
the above definition of “fallacy,” the
syllogism would not be treated as fallacious because it
is not deceptive. Nevertheless, the fallacy committed
here is formally the syllogistic four term fallacy and informally
the fallacy of equivocation. The middle term
“nothing” is being used in two different senses
of the word: a positive sense in the first premise
and a negative sense in the second premise.
But a Penny is better than nothing;
∴ A Penny is better than Heaven.
- The notion of validity is normally applied to deductive
arguments only. So the above proposed definition of
“fallacy” would not address the incorrectness
or unacceptibility of inductive, probabilistic, or informal
- Moreover, in the case of petitio
principii (circular reasoning), its fallacious aspect is
not its deductive invalidity, but instead its deceptiveness. This
is one reason many argumentation theorists argue that some informal
fallacies are not necessarily viewed as arguments per se
but instead viewed as deceptive techniques or rule violations.
Additionally, the fallacy of complex
question (the fallacy of many questions) is not prima
facie an argument — it couches an unwarranted
presupposition within a question.
- So a fallacy is simply a mistake in reasoning which is
often misleading or deceptive. A useful short definition is
provided by J. Weldon:
“A Fallacy is a violation of logical principle
disguised under a show of validity.”
A fallacious argument either does not prove, or does not
provide sufficient evidence for, its conclusion.
- The definition of fallacy is assumed here as a working
definition, even though the definition is inadequate insofar as
it presupposes a set of known, agreed-upon rules for all forms
of systematic reasoning.
- Some logicians maintain that informal fallacies must occur
with some frequency to count as fallacy. The view
taken here is any error in reasoning is a fallacy no matter
how seldom it occurs, but such fallacies are not usefully
designated with a stipulative definition.
- This definition is not consistent with the pragma-dialectical
definition of “fallacy” as ”systematically
connected with the rules for critical discussion.”
Pragma-dialectic stipulates rules of behavior rather than describes
rules of what constitutes a logical mistake per se.
- These notes follow the traditional logical practice
of regarding fallacies as occurring in arguments but not
occurring in statements, premises, or beliefs.
- Single false or misleading statements are said to be
fallacies in everyday discourse, but in these notes we will
restrict the term, for the most part, to arguments. So, we
will follow a precising definition
of fallacy where a false, disparaging, or emotively significant
statement or belief is not a fallacy.
- For example, even in the U.S. electoral milieu of
“insult politics,” name-calling per se,
in an argumentative context, is not necessarily the
commission of an ad hominem fallacy unless
the proffered abusive attack on the opponent is cited as a
reason or ground for the truth of some putative conclusion.
Consider this abridged argument by presidential candidate
Donald Trump in 2016:
“This election is also about, so importantly to me,
African-American and Hispanic-American people whose
communities have been plunged into crime, poverty and
failing schools by the policies of crooked Hillary
Clinton. Believe me, she's crooked. … I say to
the African-American community, what the hell do you have
to lose? I will fix it. I will fix it. I will make it
good. I'll bring back our jobs. We'll have good education.
We'll have great safety in the inner city.”
In this argument, Mr. Trump is arguing that he will provide
safety for the inner city because it is important to him. The
personal attack on presidential candidate Hillary Clinton is
assertive, but not argumentative, consequently not a fallacy.
Even though the offensive and unsupported comment is rudely
gratuitous and violates a norm of civility, it is not a
fallacious argument with respect to the topic at issue of
inequitable issues in inner city communities. It is rather
plainly a contextually unsupported assertion. An ad
hominem insult does not always function as an ad
- In the evaluation of arguments, logicians now recognize
that each argument need be evaluated in terms of the statements in
the argument together with the context of the dialogue in which it
The evaluation of an argument apart from its context can often
result in misinterpretation of the argument.
- The framework for various kinds of fallacies depends upon a
theory of argument — e.g., what kinds of arguments
are rule-based. No matter how logic in general is described, a
fallacy can be thought of as a violation of a logical-rule
in one or more of its kinds or divisions. Whether or not
there is only one type of correct logic is a matter of some
- Different logics are such that what is fallacious in
one logic might not be fallacious in different logic. This is
not necessarily a problem since different logics are put to
different purposes. E.g.
any correct inductive argument in science is analyzable as
an invalid deductive argument in formal logic.
- Stephen Toulmin, Richard Rieke, and Allan Janik state:
“[A]rguments that are fallacious in one context
may turn out to be sound in another context.”
(The notion of “sound” for Toulmin, et al.
has to do with differing standards of evidence for different
fields of inquiry not (necessarily) with validity and truth
- In current practice, the notion of fallacy in argumentation
is interpreted in several different ways:
- In formal logic, language syntax is formulated into
argument structures with logical validity defined in terms
of rules for those structures. Validity is a necessary
condition for normative logical correctness. In semantical,
formal deductive logical theories, “fallacy”
is defined in terms of a violation of formal logical rules;
for instance, the fallacy of
the undistributed middle term occurring in Aristotelian
syllogistic logic can be interpreted as the fallacy
of affirming the consequent in symbolic
or mathematical logic.
- However, it is essential to point out that not all
violations of formal logical rules are fallacies, since
an argument might be valid on other grounds — viz.,
its semantic content. An argument might not be formally
valid but its validity might be due to an analytical
relationship in the meanings of the statements in the
argument (i.e., the what is said). Consider the
Some raptors are birds.
Formally, this argument commits the fallacy of the
undistributed middle term (as described above). Nevertheless,
the meaning of the word “hawk” includes the
notion of being a bird, so if someone understands what
the premises mean, then the conclusion of this argument
necessarily follows from reasons other than its form. It's
to be wondered if such semantic interpretations are to
be termed “arguments” at all.
Some hawks are raptors.
∴ Some hawks are birds.
- Rolf George points out that understanding an argument
involves more than just understanding its statements:
“[T]here is a further act of understanding,
viz. ‘understanding the argument.’”
And understanding the argument includes understanding its
structure, formal or informal.
- In pragmatic and dialogical argumentation theory,
a fallacy is defined as the violation of a normative
rule or conversational maxim occurring in a dialogue
or critical conversation. For instance, evading the
burden of proof in an argument or providing irrelevant
arguments both count as incorrect moves in a critical
- Presently, several significant accounts of pragmatic
dialogical norms or rules have been proposed, and in
general in those accounts a fallacy is defined as a
violation of the variously determined norms, rules, or
- Nevertheless, as these rules are not universalizable,
the notion of fallacy comes to mean different dialogue
rule infractions in different dialogue games: “[W]hat
constitutes a fallacy in one game of dialogue does not
need to constitute a fallacy in another (it could be
just a blunder, or even be entirely all right).”
- In other critical reasoning contexts, an informal fallacy
is been defined in terms of a false premise or dubious statement or
presupposition in an argument (often as an intentional deception).
Richard Whately, who revived Aristotelian logic in the nineteenth
century explains his fallacy of unduly assumed premise as
a material “nonlogical fallacy.”
For instance, consider the following “put-up”
All U.S. persons should have the right to vote.
The argument is valid — it has a correct logical structure.
However, since the first premise is not true (as of year 2019),
the argument is not sound.
All U.S. criminals are U.S. persons.
So all U.S. criminals should have the right to vote.
- Whately and some current informal logic academics consider
this argument fallacious as well because the first premise is
an unsupported statement. E.g., Ralph Johnson and Anthony
Blair explain their “problematic premise fallacy”
“[A] premise is problematic if it is introduced
into the argument without defense and is unacceptable without
this defense.” [emphasis original]
This approach has many advantages; however, in these logic
notes, this usage of “fallacious” is not followed.
First, there is no clear method for resolving all disputes as
to what is unacceptable if there is no generally acceptable
criterion of acceptability. Second the notion of fallacy acquires
an additional meaning, and in contentious disputes there may
well be no clear way to agree on generally acceptable premises.
Finally, working with low probability problematic premises is
sometimes essential in anticipating conclusions which reveal
extraordinary risk exposure.
- Instead, often arguments can be analyzed with reformulated or
revised true premises.
Some U.S. persons should have the right to vote.
In this case the argument is invalid since the “persons”
referred to in the first premise are not necessarily the same
persons referred to in the second premise. Thus, since the middle
term does not refer to each an every person in either premise,
no logical connection can be made between the other two terms.
This method of the formal translation of informal fallacies is
further discussed below in Section
VI, A, 1-2.
All U.S. criminals are U.S. persons.
All U.S. criminals should have the right to vote.
- The choice between the acceptability of the fallacy of
a false or problematic premise and an unsound argument in such
cases is ultimately dependent upon how “fallacy”
is to be defined.
- Another use of the term “fallacy” not followed
here includes the shift from one dialogue model to a different
kinds of errors are not emphasized in these notes even though
examples of these uses are occasionally provided in the
discussions of various informal fallacies.
Paralogisms, Sophisms, and Paradoxes:
- A formal fallacy is termed a paralogism when its
conclusion does not follow from its premises, and the illogical
reasoning is believed valid by the proponent of that argument.
The argument is presented with no intention of deception.
In addition, a paralogism can be advanced as a topic for
disputation in the examination of the question why specific
premises an an argument seem to warrant its conclusion but do not
actually do so. Usually and etymologically, a paralogism is
more or less synonymous with a definition of formal fallacy as
the violation of a rule of inference.
- When a proponent's illogical reasoning is intentionally
advanced in order to deceive other persons, the fallacy is called
a sophism. In sum, as Immanuel Kant writes, a fallacious
argument, “when one deceives himself with it, is a paralogism;
and when he endeavours to deceive others with it, a sophism.”
[Kant, Logic trans. Richardson ¶ 90.]
- A paradox is an apparently good argument based on
apparently true premises which reach a contradictory conclusion.
- A paradox is resolved by discovery of the faulty assumptions
or by an emendation or change of a rule of logic. Traditionally,
faulty assumptions were termed fallacies of a false premise. In
these notes paradoxes of this kind are viewed as unsound arguments.
- The study of paradoxes is often useful for revealing mistaken
ordinary presuppositions in our thinking.
Three Basic Types of Fallacies: Informal,
Deductive, and Inductive:
Since most fallacies arise from either the lack of premises or a
confusion of premises, their identification is dependent upon what
must be supplied in order to support the conclusion. And as Whately
”[I]t must be often a matter of doubt, or, rather of
arbitrary choice, not only to which genus each kind of
fallacy should be referred, but even to which kind to refer any one
individual fallacy …” [emphasis original]
Fallacies cannot be as clearly classified as the types of arguments can
be classified. Fallacy classifications overlap. Some informal fallacies
can be formally explained; many inductive fallacies can be explained
Thus, arguments can be assessed by different standards depending
upon their semantic content and purpose. (Other schemes of
classification of fallacies are also used in the literature but are
not reviewed here.) In these notes, all fallacies will be classified
as either deductive and inductive. Informal fallacies are considered
one type of inductive argument rather that a separate category
differing from deductive and inductive arguments.
Nevertheless, we will study informal fallacies as if it were a separate
subject from that of inductive arguments.
: those dependent upon language —
, a fallacy that arises from the content
the subject of an argument (the what
is said), not the
, the grammatical structure per se
it is said). These notes include informal fallacies
as a type of nonformal inductive arguments.
Historically, from Aristotle, most informal fallacies are
classified as material fallacies, “non-logical,”
or extra dictionem fallacies since such fallacies
are not due to the violation of formal (in
dictione) rules for valid structure of arguments but rather
due to the consistency of the semantic matter, meaning, or information
Informal fallacies, in general, usually arise in ordinary
language contexts from mistakes in written and oral argumentation,
persuasion and debate.
In other words, traditional informal fallacies are not usually
considered breaches of the rules of formal logic; instead, informal
fallacies occur in disputes over specific questions at issue which
are more clearly understood by other methods of analysis than those
of formal logic.
- When an argument is valid with at least one premise false,
the truth of the conclusion does logically follow from the
premises, but historically, such arguments were considered to
be a type of material (informal) fallacy since the conclusion
wasn't proved to be true even though the argument was valid.
(If you are not clear on the meaning of these terms, review the
explanations offered on the truth, validity,
and soundness webpage.)
Some logicians today want to restrict the term “fallacy”
only to a mistake in reasoning. Thus, these logicians consider
a valid argument with at least one false premise good reasoning
even though the truth of the conclusion has not been proved.
So rather than identifying such an argument as a fallacy, they
state that the argument is valid but not sound, and the claim
the conclusion has not been proved true. The phrase “follows
logically” here can be described by means of the counterfactual
“If the premises were true in the argument,
then the conclusion would necessarily be true.”
Consider, for example, the following argument presented by
“Let us consider, therefore, the arts and sciences
in themselves. Let us see what must result from their
advancement … Their evil origin is, indeed, but
too plainly reproduced in their objects. … [T]he
labours of the most enlightened of our learned men and
the best of our citizens are of so little utility …
[their] waste of time is certainly a great evil; but still
greater evils attend upon literature and the arts. One
is luxury … can it be denied that rectitude of morals
is essential to the duration of empires, and that luxury
is diametrically opposed to such rectitude?”
Rousseau argues here that since the evil origin and nature
of the arts and science lead to luxury, and luxury is opposed
to morality, the arts and sciences are immoral.
This valid argument rests on false premises and so is unsound.
Some researchers simply see the argument as valid based on false
assumptions and others classify it as also a case of the
fallacy of false cause or even the genetic fallacy.
- Formal Translation of Informal Fallacies: When some
informal fallacies are viewed as (formal)
arguments, these arguments can be found valid when the missing
premise is charitably found. But the argument is not sound
because the missing premise must of necessity be false in order
to reconstruct the enthymeme into a valid argument.
David M. Godden cogently argues that the interpretation of
informal arguments as deductive must be based on the context in
which the argument is given and evidence that the arguer intends
or ought to intend the argument to be deductive.
consider the following ad hominem
fallacy stated by Voltaire:
“Excessive pride and envy have destroyed Jean-Jacques
[Rousseau], my illustrious philosopher. That monster dares
speak of education! A man who refused to raise any of his
sons and put them all in founding homes! He abandoned his
children and the tramp with whom he made them.”
So, the ad hominem part of the sorites can be roughly
translated as follows:
Rousseau is an abandoner of his children and their mother.
On the one hand, since in this passage from Voltaire, Voltaire
seems to express no doubt that anyone who abandons his children
and their mother does not have the wisdom required to speak
meaningfully about education, the context of the argument indicates
his conclusion is intended to follow with certainty. Supplying the
missing premise to produce a valid argument yields the following:
Rousseau is not an educational authority.
The quotation is an informal fallacy; the completed enthymeme
is a valid but unsound argument with a false major premise.
[No educational authority is an abandoner of his children
and their mother.] F
Rousseau is an abandoner of his children and their mother.
∴ Rousseau is not an educational authority.
On the other hand, the recognition of Voltaire's keen wit in
other contexts might suggest that he would be well aware of the
tenuousness of the argument. So, perhaps we should supply a
more conservative premise:
This translation results in the fallacy of the undistributed middle. Moreover, if the
major premise is converted to “ Some educational authorities
are not abandoners of their children and their mother,” the
resultant syllogism would commit fallacy of the illicit major.
Some abandoners of their children and their mothers are not
Rousseau is an abandoner of his children and their mother.
∴ Rousseau is not an educational authority.
- The first formal analysis of this informal argument above
suggests a reason why one definition of “fallacy” in the
nineteenth century was “A false belief, whether due to
correct reasoning from untrue premises … or to incorrect
reasoning from true ones.” And this analysis
would also be consistent with Richard Whately's fallacy of unduly
assumed premise discussed above.
- The second and third formal analyses reinforces H.W.B.
Joseph's observation that “The same inconclusive argument
may often be referred at will to this or that head of fallacies.”
- Voltaire's argument and the subsequent analyses also clearly
illustrate why Richard Whately writes that the same argument can
be analyzed in different ways:
“Since in any Argument one Premiss is usually suppressed
it frequently happens, in the case of a Fallacy, that the hearers
are left to the alternative of supplying either a
Premiss which is not true, or else, one which
does not prove the Conclusion.”
In other words, often, to avoid a problematic premise in a valid
argument, the argument can only be interpreted with a true premise
at the price of an invalid argument. Or, as J.S. Mill writes
about arguments such as these:
“[S]ome might assent to the false premise; others
allow the unsound syllogism.”
- The pragma-dialectical theory of fallacy developed by the
Amsterdam School (Frans H. van Eemeren and Rob Grootendorst)
defines fallacies as violations of rules for critical
Douglas Walton enumerates six conditions or characteristics for
fallacy in his earlier pragmatic theory. Both
accounts depend upon an interpretation of multiple conditions
with considerable open texture involving judgments involving
criteria of reasonableness, acceptableness, relevance, and
- Logic and critical reasoning textbooks (and, unfortunately
these lecture notes!) usually explain informal fallacies as
specific exhibits with slight attempt to analyze them in the
general context in which they occur. Informal fallacies, however,
are contextually dependent and require analysis in terms of their
circumstances of use. A particular fallacy or argument is presumed
to occur within a particular context of a dialogue, conversation,
or extended argument even though the context and content usually
develops and evolves as the discourse progresses. The context is,
so to speak, the common ground or common knowledge of the
: those not dependent on the content of
language. Formal fallacies arise from an error in the logical
form or structural grammar of an argument; they are analyzed
independently from their informational content.
- Formal fallacies often arise from errors arising in poorly
formed deductive systems of logic. In deductive arguments, the
conclusion is claimed to logically follow from the premises with
- The ideal of formal logic is based on (1) the belief that validity
in arguments is independent of, yet abstracted from, the relationships
of material or informational content of statements, and (2) the belief
that the formal logical relations are independent of the psychology and
context of intention and circumstances of the assertions.
- Currently, as noted above, fallacies can be studied from different
viewpoints. An argument can be found fallacious by a formal standard
of validity and yet be seen as valid from a semantic point of
view. Or an argument can appear to be valid from a formal point of view
and yet be seen as invalid from ambiguity.
Additionally, some invalid formal arguments are correct or strong
inductive arguments. The usefulness of an argument depends upon its
purpose and context.
arise from mistakes in
inductive arguments where the conclusion is claimed to
follow from the premises with some degree of probability.
vary in strength.
The assignment of probabilities to statements is often arbitrary and
It's important to realize that the semantic content of many
formal and informal fallacies provide evidence for the truth of their
So, a correct or an acceptable inductive argument can also be analyzed as
an invalid formal argument depending on the context of the analysis.
- Inductive fallacies have no clear historical standard of
classification. Many traditional inductive arguments depend upon
semantic content rather than argument forms so many inductive
fallacies are informal fallacies: e.g. converse accident
(hasty generalization), accident, causal fallacies, false or
faulty analogy, genetic fallacy, and ad ignorantiam.
- J.S. Mill points out that induction proceeds from facts; when
these facts are mistaken, fallacies based on poor observations or
mistaken inferences result.
Examples of these types of fallacies include confirmation bias,
preconceived opinion, faulty generalization, suppressed evidence, and
- These and other presumptive fallacies are common in inductive
logic, especially in the use of formal scientific methods, including
probability and statistics.
- Inductive methods used in causal reasoning, probability, and
statistics are based on formal rules, and consequent
fallacies in these areas of inductive logic are violations of
formal rules. Analyses of informal fallacies using these methods
Chart of Formal, Informal, and Inductive Fallacies
The following chart of fallacies, with some suggestive examples, is
an indication of some of the terrain to be discussed in this course:
The following Google Ngram of the frequency of usage of the main
divisions of logic suggest the historical periods of active interest
in these fields of inquiry:
FIG. 1. Historical Frequency of Use of formal logic,
inductive logic, and informal logic in Google Books 1800-2008
There is hardly a subject that dies harder or has changed so little
over the years. After two millennia of active study of logic and, in
particular, after over half of that most iconoclastic of centuries,
the twentieth A.D., we still find fallacies classified, presented and
studied in much the same old way. … The truth is that nobody,
these days, is particularly satisfied with this corner of logic. The
traditional treatment is too unsystematic for modern tastes.
C.L. Hamlin, Fallacies (London: Methuen & Co., Ltd.,
1970), 9, 11.
Title links go to cited page
“[A]ll constituents of sentences not covered
by the assertoric force do not belong to scientific exposition;
but they are sometimes hard to avoid, even for one who sees the
danger connected with them.”
Gottlob Frege, “Logical Investigations Part I Thoughts,”
trans. Peter Geach and R. H. Stoothoff Collected Papers on
Mathematics, Logic, and Philosophy (Oxford: Basil Blackwell,
1984), 357. doi:
“[T]he term ‘fallacy” is our most general term for
criticizing any general procedure used for the fixation of beliefs
that has an unacceptably high tendency to generate false or unfounded
beliefs, relative to that method of fixing beliefs.”
[Robert J. Fogelin and Timothy J. Duggan, “Fallacies”
Argumentation 1 no. 3 (September 1987), 255-262. doi:
This definition avoids the difficulty of counting valid circular arguments
fallacies. Again, though, the psychological aspect of this definition
and its application as “any general procedure” mark the
definition as too broad as Harvey Siegel and John Biro point out.[Harvey
Siegel and John Biro, “Epistemic Normativity, Argumentation, and
Fallacies,” Argumentation 11 no. 3(August. 1997),
279. doi: 10.1023/a:1007799325361
33. Jeremy Bentham, The Book of Fallacies:
From Unfinished Papers of Jeremy Bentham (London: John and
H.L. Hunt, 1824), 1. ↩
“A fallacy is a fallacious argument.
Someone who merely makes false statements, however absurd,
is innocent of fallacy unless the statements constitute
or express an argument.” [emphasis Hamlin]
, 224. Compare with the
Frans H. van Eemeren, et al. definition of fallacy:
“Fallacies are violations of the rules for critical
discussion that prevent or hinder the resolution of a
difference of opinion.”
Frans H. van Eemeren, et al. Argumentation: Analysis,
(New York: Routledge Francis
and Taylor Group, 2016), 109. doi:
Douglas H. Walton extends this “Amsterdam School”
definition of fallacy as follows:
“A fallacy is regarded as an argumentation technique,
based on an argumentation scheme, misused to block the goals
of a dialogue in which two parties are reasoning together.”
Douglas H. Walton, A Pragmatic Theory of Fallacy
(Tuscaloosa, Alabama: University of Alabama Press, 1950), xi. isbn13: 9780817307981
Rules and schemes such as these often prove to be problematic
in application to serious disagreements since criteria for what
prevents, hinders, or blocks the resolution of a disagreement are
often themselves subject to disagreement among the disputants.
Moreover, different types of dialogue and discussion require
different rules, and informal fallacies occur in various other
contexts than those of two-party argumentation.↩
“This approach amounts to applying an appropriate
logical system in analyzing a particular fallacy. Every
fallacy needs, so to speak, its own logic. For practical
purposes this approach is not very realistic.”
F.H. van Eemeren and R. Grootendorst“ A
Transition Stage in the Theory of Fallacies,“
Journal of Pragmatics 13 no.1 (February 1989),
Although this is a bit of an exaggeration, they have a point. However,
this is a consequence of the current dappled nature of informal fallacy
“1. A fallacy is a failure, lapse or error, subject to
criticism, correction or rebuttal.
2. A fallacy is a failure that occurs in what is supposed to
be an argument.
3. A fallacy is associated with a deception or illusion.
4. A fallacy is a violation of one or more of the maxims of
reasonable dialogue or a departure from acceptable procedures
in that type of dialogue.
5. A fallacy is an instance of an underlying, systematic kind
of wrongly applied techniques of reasonable argumentation.
6. A fallacy is a serious violation, as opposed to an incidental
blunder, error or weakness of execution.”
Douglas H. Walton, Methods
of Argumentation (New York: Cambridge University Press, 2013),
10.1017/CBO9781139600187. Again, these enumerated characteristics
are debatable as precisely stated criteria are not specified for the
identification of occurrences of failure, lapse, deception, serious
violation, reasonable dialogue, wrongly applied techniques, and so
Readings on Fallacies
Dowden, Bradley. “Fallacies
,” Internet Encyclopedia of Philosophy
ed. Edward N.
Zalta (Fall 2019), np.
Finocchiaro, Maurice A. “Fallacies and the Evaluation of
Reasoning,” American Philosophical Quarterly
18 (March, 1981), 13-22. Also in Arguments About Arguments:
Systematic, Critical, and Historical Essays in Logical Theory
(Cambridge: Cambridge University Press, 2005). doi:
Finocchiaro, Maurice A. “Informal Logic and the Theory
,” Informal Logic
6 no. 2 (January, 1984).
Fogelin, Robert J., and Timothy J. Duggan. “Fallacies,”
1, no. 3 (September, 1987): 255–262. doi: 10.1007/bf00136777
Govier, Trudy. A Practical Study of Arguments
(Belmont, CA: Wadsworth, 2010). doi:
Govier, Trudy. “Who Says There Are No Fallacies?,” Informal
5 no. 1.(Spring 1984), 2-10. doi: 10.22329/il.v5i1.2741
Grootendorst, Rob. “Some Fallacies about Fallacies,” in
Argumentation: Across the Lines of Discipline
H. van Eemeren, Rob Grootendorst, J. Anthony Blair, and Charles
Willard (Dordrecht: Foris, 1987), 331-342. doi:
Hamlin, C.L. Fallacies
(1970 Willersey, U.K: Vale
Hansen, Hans V. and Robert C. Pinto, eds. Fallacies:
Classical and Contemporary Readings
PA: Pennsylvania State University Press, 1995). http://www.psupress.org/books/titles/0-271-01416-4.html
Hansen, Hans V. “Fallacies
,” Stanford Encyclopedia of Philosophy
Edward N. Zalta (Fall 2019), np.
Hansen, Hans V. “A Searchable
Bibliography of Fallacies — 2016
36 no. 4 (December, 2016), 432-472. doi:
Hansen, Hans V. “The
Straw Thing of Fallacy Theory: The Standard Definition of
no. 2 (June 2002), 133-155. doi: 10.1023/A:1015509401631
Hintikka, Jaakko. “The Fallacy of Fallacies,”
1 no. 3(September 1987), 211-238. doi: 10.1007/bf00136780
Hintikka, Jaakko. “Logic as a Field of Knowledge,”
72 no. 1 (January, 1989), 3-24. doi: 10.5840/monist19897211
Johnson, Ralph H. “The Blaze of Her Splendors: Suggestions About
Revitalizing Fallacy Theory,” Argumentation,
no. 3 (September, 1987), 239-253. doi:
Johnson, Ralph H. “Hamlin on the Standard Treatment,”
Philosophy and Rhetoric
23 no. 3 (1990), 153-167.
Johnson, Ralph H. “Massey on Fallacy and Informal Logic: A Reply”
80 no. 3 (September 1989), 407-426. doi: 10.1007/bf00869583
Massey, Gerald J. “The
Fallacy Behind Fallacies
” Midwest Studies in
6 no. 1 (September, 1981), 489-500. (follow link
McKay, Thomas J. “On Showing Invalidity,” Canadian Journal of Philosophy
14 no. 1 (January 1984), 97-101. doi:
Rips, Lance J. “Argumentative
Thinking: An Introduction to Psychology and Argumentation
29 no. 4 (December 2009), 327-336. doi:10.22329/il.v29i4.2902
Tindale, Christopher W. Fallacies and Argument
(Cambridge: Cambridge University Press,
2007). doi: 10.1017/cbo9780511806544
van Eemeren, Frans, Bart Garssen, and Bert Meuffels.
and Judgments of Reasonableness
(New York: Springer,
van Eemeren, Frans H., et al. Fundamentals of Argumentation Theory: A Handbook
of Historical Backgrounds and Contemporary Developments
[Google preview] (Mahwah, New Jersey: Lawrence Erlbaum, 1996). doi: 10.2307/358423
Walton, Douglas N. “Defeasible
Reasoning and Informal Fallacies
179 no. 3 (Apr. 2011) 377-407. doi:
Walton, Douglas N. Informal
Logic: A Pragmatic Approach
2nd. ed. (Cambridge: Cambridge
University Press, 2008). doi:
Walton, Douglas N. A Pragmatic Theory of Fallacy
2nd. ed. (Tuscaloosa, Alabama: Univ. of Alabama Press: 2003). preview
Walton, Douglas N. “What is a Fallacy?,” in
Argumentation: Across the Lines of Discipline
H. van Eemeren, Rob Grootendorst, J. Anthony Blair, and Charles
Willard (Dordrecht: Foris, 1987), 329. doi:
Weinstock, Michael, Yair Neuman and Iris Tabak. “Missing
the Point or Missing the Norms? Epistemological Norms as Predictors
of Students' Ability to Identify Fallacious Arguments,”
Contemporary Educational Psychology
29 no. 1 (January, 2004),
Woods, John. “A History of the Fallacies in Western Logic,” in
Handbook of the History of Logic
eds. Dov M. Gabbay, Francis
Jeffry Pelletier, and John Woods (Amsterdam: North Holland, Elsevier, 2012),
Woods, John. “Is
the Theoretical Unity of the Fallacies Possible?
,” 16 no. 2
(Spring, 1994), 77-85. doi: