Logical Fallacies

 A fallacy is a misleading or false argument or belief.  What follows
is a list of the most common informal and formal logical fallacies.
Learn these and be able to spot logical fallacies in your (and others')
reasoning.

ACCENTUS

 One of the Fallacies of Ambiguity, which arises from the emphasis (the
accent) placed on a word or phrase.

AFFIRMING THE CONSEQUENT

 An argument based on a hypothetical statement, and the truth of the
consequent to the truth of the antecedent.  In the SYLLOGISM below, A is
the antecedent and C is the consequent:

A implies C
C is true                  <-- Affirming the consequent
______________
Therefore:  A is true


AMBIGUITY

 An argument in the course of which at least one term (such as "rights")
is used in different senses.  Also known as equivocation.  There are
several types of "fallacies of ambiguity," including REIFICATION,
EQUIVOCATION, AMPHIBOLY, COMPOSITION, DIVISION, and ACCENTUS.

AMPHIBOLY

 A type of Fallacy of Ambiguity where the ambiguity involved is of an
"amphibolous" (equivocal, uncertain) nature.  Amphiboly is a syntactic
error. The fallacy is caused by faulty sentence structure, and can
result in a meaning not intended by the author.  "The department store
now has pants for men with 32 waists." (How many waists do you have?)

ARGUMENTUM AD ANTIQUITAM

 A fallacy of asserting that something is right or good simply because
it is old; that is, because "that's the way it's always been."

ARGUMENTUM AD BACULUM

 An argument that resorts to the threat of force to cause the acceptance
of the conclusion.  Ad baculum arguments also include threats of fear to
cause acceptance (e.g., "Do this or you'll go to Hell when you die!" or
"I made him an offer he couldn't refuse.").

ARGUMENTUM AD CRUMENAM

 Fallacy of believing that money is a criterion of correctness; that
those with more money are more likely to be right.  "If he's so stupid
why is he so rich?" The reverse of a. ad crumenam is a. ad lazarum.

ARGUMENTUM AD HOMINEM

 An argument that attempts to disprove the truth of what is asserted by
attacking the speaker rather than the speaker's argument.  Another way
of putting it: Fallacy where you attack someone's character instead of
dealing with issues.  The two basic types of ad hominem arguments: are
1) abusive, and 2) circumstantial.  This is the most common form of
Logical Fallacy.

ARGUMENTUM AD IGNORANTIAM

 An argument that a proposition is true because it has not been shown to
be false, or vice versa.  Ad ignorantium arguments are also known as
"appeals to ignorance." This fallacy has two forms:

1.  The statement is true, because it has not been proven false.
2.  The statement is false, because it has not been proven true.

ARGUMENTUM AD LAZARUM

 A fallacy of assuming that because someone is poor he or she is sounder
or more virtuous than one who is wealthier.  -- "responsible breeders
don't make money." This fallacy is the opposite of the informal fallacy
a. ad crumenam.

ARGUMENTUM AD MISERICORDIAM

 An argument that appeals to pity for the sake of getting a conclusion
accepted (or for fundraising).

ARGUMENTUM AD NAUSEUM

 The incorrect belief that an assertion is more likely to be true the
more often it is heard.  An a. ad nauseum is one that employs constant
repetition in asserting a statement is the truth.  Dr. Goebbel's Big Lie
Theory.

ARGUMENTUM AD NOVITAM

 A fallacy of asserting that something is more correct simply because it
is new or newer than something else.  Or that something is better
because it is newer.  -- "we've tried the other way for a while and it's
failed, let's try something (anything) ." This type of fallacy is the
opposite of a. ad antiquitam.

ARGUMENTUM AD NUMERAM

 A fallacy that asserts that the more people who support or believe a
proposition then the more likely that that proposition is correct; it
equates mass support with correctness.

ARGUMENTUM AD POPULUM

 An argument that appeals to the beliefs of the multitude.  Another way
of putting it: Speaker deals with passions of audience rather than with
salient issues.  This fallacy is also known as "Appeal to Tradition" Ad
populum arguments often occur in 1) propaganda, 2) demagogy, and 3)
advertising.

ARGUMENTUM AD VERECUNDIAM

 An argument in which an authority is appealed to on matters outside
his/her field of authority.  (like veterinarians dispensing medical
advice).  a.ad verecundiam also refers to a fallacy of simply resorting
to appeals to authority (like "Doctor" Tom Regan)

BEGGING THE QUESTION (CIRCULAR REASONING)

 An argument that assumes as part of its premises that the conclusion is
true. Another way of saying this is: Fallacy of assuming at the onset of
an argument the very point you are trying to prove.  This Fallacy is
also known by the Latin "PETITIO PRINCIPII"or "CIRCULUS IN PROBANDO."

BIFURCATION

 Also referred to as the "black and white" fallacy, bifurcation is the
presentation of a situation or condition with ONLY TWO alternatives,
whereas in fact other alternatives exist or can exist.

COMPOSITION

 An argument which assumes that a whole has a specific property solely
because its various parts have that property.  -- "Because ALF is a
terrorist organization (and ALF is part of PETA) > all PETA members
condone terrorism." Composition is a type of Fallacy of Ambiguity.

CONVERTING A CONDITIONAL

 Description: If A then B, therefore, if B then A.  <<<NOT!!!

CUM HOC ERGO PROPTER HOC

 A fallacy of correlation that links events because they occur
simultaneously; one asserts that because two events occur together they
are causally related, and leaves no room for other factors that may be
the cause(s) of the events.  This fallacy is similar to the "post hoc"
fallacy.

DENIAL OF THE ANTECEDENT

 An argument in which one infers the falsity of the consequent from the
truth of a hypothetical proposition, and the falsity of its antecedent.

A implies B
Not-A
____________
Therefore:  Not-B

DIVISION

 An argument in which one assumes that various parts have a property
solely because the whole has that same property.  Division is a type of
Fallacy of Ambiguity -- the inverse of COMPOSITION.

EQUIVOCATION

 An argument in which an equivocal expression is used in one sense in
one premise and in a different sense in another premise, or in the
conclusion. Equivocal means 1) of uncertain significance; not
determined, and 2) having different meanings equally possible.
Equivocation is a type of Fallacy of Ambiguity.  The opposite of
equivocation is "UNOVOCATION," in which a word always carries the same
meaning through a given context.

FALLACY OF INTERROGATION

 The question asked has a presupposition which the answerer may wish to
deny, but which he/she would be accepting if he/she gave anything that
would count as an answer.  Any answer to the question "Why does this
event happen?" presupposes that the event does indeed happen.


FALSE ANALOGY

 An analogy is a partial similarity between the like features of two
things or events on which a comparison can be made.  A false analogy
involves comparing two things that are NOT similar.  Note that the two
things may be similar in superficial ways, but not with respect to what
is being argued.

IGNORATIO ELENCHI

 An argument that is supposed to prove one proposition but succeeds only
in proving a different one.  IGNORATIO ELENCHI stands for "pure and
simple irrelevance."

ILLICIT PROCESS

 A syllogistic argument in which a term is distributed in the
conclusion, but not in the premises.  One of the rules for a valid
categorical syllogism is that if either term is distributed in the
conclusion, then IT MUST BE DISTRIBUTED IN THE PREMISES.  There are two
types of Illicit Process: Illicit Process of the Major Term and Illicit
Process of the Minor Term.

PLURIUM INTERROGATIONUM - COMPLEX QUESTIONS

 A demand for a simple answer to a complex question.

NON CAUSA PRO CAUSA

 An argument to reject a proposition because of the falsity of some
other proposition that SEEMS to be a consequence of the first, but
really is not.

NON-SEQUITUR - DOES NOT FOLLOW

 An argument in which the conclusion is not a necessary consequence of
the premises.  A conclusion drawn from premises that provide no logical
connection to it.

PETITIO PRINCIPII

 The same as "Begging the Question" This argument assumes its conclusion
is true but DOES NOT SHOW it to be true.  Petitio principii has two
forms:

1.  P is true, because P is true.
2.  P is true, because A is true.   And A is true because B is true.
    And B is true because P is true.

POST HOC, ERGO PROPTER HOC

 An argument from a premise of the form "A preceded B" to a conclusion
of the form "A caused B." Simply because one event precedes another
event in time does not mean that the first event is the cause of the
second event.  This argument resembles a fallacy known as a HASTY
GENERALIZATION.

QUATERNIO TERMINORUM

 An argument of the syllogistic form in which there occur four or more
terms. In a standard categorical syllogism there are ONLY THREE TERMS: a
subject, a predicate, and a middle term.

RED HERRING

 A fallacy when irrelevant material is introduced to the issue being
discussed, such that everyone's attention is diverted away from the
points being made, and toward a different conclusion.  It is not
logically valid to divert a chain of reasoning with extraneous points.

REIFICATION

 To reify something is to convert an abstract concept into a concrete
thing. Reification is a Fallacy of Ambiguity.  Reification is also
sometimes known as a fallacy of "HYPOSTATIZATION".

SECUNDUM QUID (HASTY GENERALIZATION)

 An argument in which a proposition is used as a premise without
attention given to some obvious condition that would affect the
proposition's application.  This fallacy is also known as the "HASTY
GENERALIZATION." It is a fallacy that takes evidence from several,
possibly unrepresentative, cases to a general rule; generalizing from
few to many.  NOTE THE RELATION TO STATISTICS: Much of statistics
concerns whether or not a sample is representative of a larger
population.  The larger the sample size, the better the
representativeness.  Note also that the opposite of a hasty
generalization is a sweeping generalization.

SHIFTING THE BURDEN OF PROOF

 The burden of proof is always on the person making the assertion or
proposition.  Shifting the burden of proof, a special case of
"ARGUMENTUM AD IGNORANTIUM," is a fallacy of putting the burden of proof
on the person who denies or questions the assertion being made.  The
source of the fallacy is the assumption that something is true unless
proven otherwise.

SPECIAL PLEADING

 Special pleading is a logical fallacy wherein a double standard is
employed by the person making the assertion.  Special pleading typically
happens when one insists upon less strict treatment for the argument
he/she is making than he or she would make when evaluating someone
else's arguments.

STRAW MAN

 It is a fallacy to misrepresent someone else's position for the
purposes of more easily attacking it, then to knock down that
misrepresented position, and then to conclude that the original position
has been demolished.  It is a fallacy because it fails to deal with the
actual arguments that one has made.

SWEEPING GENERALIZATION

 Also known by the Latin term "DICTO SIMPLICITER", a Sweeping
Generalization occurs when a general rule is applied to a particular
situation in which the features of that particular situation render the
rule inapplicable.  A sweeping generalization is the opposite of a hasty
generalization.

TWO WRONGS MAKE A RIGHT (TU QUOQUE)

 Two wrongs never add up to a right; you cannot right a wrong by
applying yet another wrong.  Such a fallacy is a misplaced appeal to
consistency.  It is a fallacy because it makes no attempt to deal with
the subject under discussion.

UNDISTRIBUTED MIDDLE

 A syllogistic argument in which the middle term of a categorical
syllogism is not distributed in AT LEAST ONE of the premises.