LOGIC
INFORMAL FALLACIES
A.
DEFINITION
Etymology: From Latin, fallacia:
deliberate deceit or trick. Cf. Greek sophisma: skillful act, clever
device, sly trick, specious argument.
Definition: A logical fallacy is, generally, an error or defect in
reasoning (fallacious argument) that exhibits the following specific
characteristics:
1. It is an incorrect,
defective form of reasoning that differs from a merely factual error
(false premises). In other words, the relation between the premises
and conclusion is logically mistaken, i.e., the conclusion does not follow
from the premises. The premises provide irrelevant evidence or
insufficient evidence. Hence, the argument is invalid (deductive
arguments) or weak (inductive arguments).
2. It is a common yet persuasive type of reasoning error that
has proven over time its power to deceive people on a regular basis. As
such, fallacies have been categorized and catalogued since Aristotle’s
Sophistical Refutations, throughout the middle ages and modern period,
and up to the present day. They are, therefore, not merely any mistaken
inference, but a pervasive and persuasive class (general type, form,
pattern, structure) of fallacious reasoning.
3. Accordingly, a fallacy is specious: it only appears or seems to be
a good argument. However, when its initial plausibility is carefully
examined it turns out to be an imposter, counterfeit, deceptive device,
trick, trap, pretender, or sophism.
Arguments, like men, are often pretenders.
—Plato (c.427-347 BCE)
It would be a very good thing if
every trick could receive some short and obviously appropriate name, so that
when anyone used this or that particular trick, he could at once be reproved
for it.
—Arthur Schopenhauer (1788-1860)
B.
TYPES OF FALLACIES
Before examining the types of
fallacies, it is helpful to distinguish between the form and
content of an argument. The form of an argument is its reasoning
pattern or structure. In contrast, the content of an argument is its
specific subject matter. Examples:
All humans are
mortal All politicians are saints
All logicians are human All liberals are politicians
All logicians are mortal All liberals are saints
These two arguments exhibit an identical form by means of, or
through, their different content.
Identical Argument Form:
All As are Bs
All Cs are As
All Cs are Bs
The two arguments above substitute different content for the
symbolic variables A, B, and C. As such, they are said to instantiate
(be an instance of) a particular argument form. When a deductive
argument instantiates a correct argument form it is called valid,
i.e., the conclusion follows from the premises with strict necessity or,
stated alternately, the conclusion must be true if the premises are true.
1. Formal Fallacies: The form of the argument is
defective. Formal fallacies only apply to deductive arguments with
identifiable reasoning patterns. Accordingly, a deductive argument that does
not instantiate a correct (valid) argument form is said to contain or
exhibit a formal fallacy. Two examples follow:
a) Affirming the Consequent: This fallacy is an argument of the form
"A implies B, B is true, therefore A is true".
If a supernatural being created
the universe, then we would see order and organization everywhere.
We do see order and organization
everywhere.
Therefore, a supernatural being did
create the universe.
If A then B
B is true
Therefore,
A is true
b) Denying the Antecedent:
This fallacy is an argument of the form "A implies B, A is false, therefore
B is false".
If Myrth York is elected governor of RI, then RI will have a governor who
supports same-sex marriages.
Myrth York will not be elected
governor of RI.
Therefore, RI will not have a
governor who supports same-sex marriages.
If A then B
A is false
Therefore, B is false
Both of these formal fallacies are deceptively persuasive. We often
uncritically assume that if the hypothetical proposition (if A then B) is
true, then the similar, yet logically distinct, hypothetical proposition (if
B then A) must also true (Affirming the Consequent). For example, if
there is smoke then there is fire, and if there is fire then there is smoke.
But the hypothetical implication (if…then relation) is unidirectional (from
A to B), not bidirectional (from A to B and from B to A). Also, we
often uncritically assume that if the truth of A implies the truth
of B, then it must also be the case that the falsity of A implies the
falsity of B (Denying the Antecedent). But they are by no
means logically equivalent.
2. Informal fallacies:
The fallacy consist in the content and “can be detected only through
analysis of the content of the argument" (Hurley, p.119). Classifications of
informal fallacies differ, both historically and among contemporary
logicians. For example, Aristotle identified only 13 fallacies and divided
them into two categories: those related to language and those not related to
language. In contrast, some contemporary logicians identify numerous (over
100) fallacies and divide them into several (5-10) classifications.
Fallacies of relevance, presumption, and ambiguity are quite standard. We
will follow Hurley’s classification, specifically fallacies of relevance and
weak induction.
C. REASONS WHY
FALLACIES ARE COMMITTED
1. Deliberate Intent:
Knowingly utilizing fallacious reasoning in order to persuade someone to
believe or do X, where X will benefit the arguer(s). The arguer typically
has an interest (political, economic, personal, psychological, etc.)
in your accepting and/or acting upon their thesis. Examples:
- politicians
want your vote
- dictators
want to exploit
your passions and prejudices
- advertisers
want you to
purchase their product
- scam
or con artists want you to do X
- fanatics
or zealots (religious, political, nationalistic, etc.) want you to
join them
2. Careless Intellectual Habits:
Unknowingly and mistakenly believing that one’s
reasoning is correct when in fact one is engaged in fallacious reasoning.
The basis of such honest yet erroneous reasoning include:
- mental laziness
- emotional disposition
- uncritical reasoning
habits
- one’s worldview
(German: weltanshaunng)
D.
GENERAL GUIDELINES FOR DETECTING AND AVOIDING FALLACIES
1. Clarity:
Consistently and persistently insist upon the exact meaning of the
thesis to which you are being asked to assent (conclusion), as well as the
exact meaning of each proposition offered as evidence for the thesis
(premises).
2. Evidential Relevance: Determine what type or kind of
evidence is pertinent to establishing the thesis under consideration and
regard with critical skepticism or suspicion any argument that does not
provide appropriate evidence.
3. Unemotional Mental Maturity:
Beware of any argument that evokes emotion of any kind,
especially if you want to agree with the thesis/conclusion of a given
argument. It is helpful in such contexts to restate the argument in
the most unemotional way possible. The desire, wish, or
need to believe X is a common and powerful obstacle to avoiding
fallacies, whether committed by oneself or others.
4. Justified Suspicion:
Be wary of arguments presented by anyone who might have a motive
to deceive you. Generally, it is reasonable to be on your guard in
social contexts in which you are exposed to individuals who stand to gain
from your assent to their argument. Specifically, it is prudent to presume
that some types of people might try to deceive you since they
have a vested interest in having their thesis accepted: politicians
want your vote, salespeople and telemarketers want you to buy something, a
prosecutor or defense attorney want you to convict or acquit, religious
fanatics or cultists want you to join their ranks, dogmatic ideologues of
all stripes want you to tow the party line, scam or con artists want to “rip
you off” (exploit you monetarily or in some other manner), etc. In general,
anyone with a personal stake in persuading you of X warrants vigilant
suspicion. This prudent logical practice should not, however, be confused
with the informal fallacy of circumstantial ad hominem. In
this fallacy someone’s argument is summarily dismissed out of hand, without
any actual evaluation of their argument, simply because the arguer stands to
gain from the acceptance of their argument. There is a considerable logical
difference between being suspicious and being prejudicial.
5. Instinctive Sense:
When you encounter a questionable argument that seems fishy to you, or
doesn’t quite sound right, try to figure out why it seems erroneous
to you, even if you can’t immediately identify what is specifically wrong
with it. We may refer to this kind of hunch as the exercise of our
instinctive or intuitive logical sense. Taking shape over time,
whether consciously or not, this logical sensibility may be very advanced,
very underdeveloped, or anywhere in between. You may ultimately conclude
that the argument is reasonable or you may decipher the logical fallacy that
prompted your initial doubts. What’s important is that you trust your
instincts, at least initially and pending further reflections.
6. Recognizing Complexity:
In contrast to formal fallacies, which instantiate one
fallacious argument form, it is possible for an argument a) to contain
more than one informal fallacy, or b) to be a border-line case
that could be equally classified as one or another informal fallacy. In the
context of everyday life (radio, TV, newspapers, political rhetoric, etc.)
quite a few arguments contain more than one fallacy. What’s important is
that you recognize that an argument is fallacious and then attempt to
determine how (one or more ways) it is fallacious. |
