Quick List

While this listing is more extensive and detailed than the basic lesson material, it's by no means complete.  Our interest here is to become acquainted with the most common kinds of fallacies that we're likely to encounter.  Taking the trouble to learn obscure fallacies wouldn't be worth the effort for most readers, unless they aim to become lawyers or professional logicians.  (Latin terms are included for the benefit of those who use this page as an Internet reference.)

It would be unrealistic to expect most people to memorize this entire list and be able to recall it on demand.  The items we most ought to commit to memory are the most general: the four general categories, "ambiguity," "formal error," "irrelevant premise," and "unwarranted assumption," and the general reasons for classifying certain statements as such.  It isn't necessary to memorize each individual fallacy; some are relatively rare, and others tend to overlap.  Moreover, even this list of fallacies isn't complete.  If we can at least recognize an error as belonging to one of the four general categories, that's good enough for most purposes.  If we hear someone remarking about an "appeal to spite," we can always look up the specifics if necessary.

Ambiguities
An ambiguity is a word, phrase, or statement that, without adequate clarification, could be interpreted in different ways.
Ambiguity is often a key element in humor, but leads to confusion when the discussion turns serious.

Fallacy

Description

Examples

Comments

equivocation

Relies on the double meaning of a term to make a questionable point.

"Igor aspired to become a great conductor.  However, he was an incompetent orchestra leader, and a failure as a ticket-taker on the railroad.  But even as he was mourning his misfortune, he was struck by lightning, and his ambition was realized after all."

This story illustrates the humorous use of a multiple-meaning word like "conductor" (i.e., music conductor, railroad conductor, electrical conductor).  But advertisers, politicians, and panderers often use such devices in a more subtle fashion to mislead the gullible—and on the whole are surprisingly successful at it.

amphiboly

Relies on an ambiguity due to sentence structure.

"Professor Hefner lectures on sexual promiscuity in room 210? They ought to post a guard there to discourage that sort of behavior!"

The structure of the sentence makes it unclear whether what goes on in room 210 is the lecture about sexual promiscuity, or the sexual promiscuity itself.

composition

Ascribes the nature of one or more parts to the whole.

"Each of this computer's components is reliable, so the computer itself must be reliable."

Composition is not always fallacious. Consider if we were to substitute "unreliable" for "reliable" in the example.

division

Ascribes the nature of a whole or a group to specific parts or individuals.

"The orchestra plays superbly. Each member must be a virtuoso."

Division is essentially composition in reverse.  Regarding this example, the qualities that make for individualistic solo virtuosity are often at odds with the requirements of disciplined cooperation necessary to an outstanding orchestra.

reification

Treats a concept as if it were an actual thing.

"God is the highest of all concepts.  The highest of all concepts must embody only the highest component concepts.  Of the concepts of existence and non-existence, existence is clearly higher.  So, God must exist."

Did you detect the point at which the reasoning shifts from concepts to things, in the middle of the third statement?  This popular argument arose among medieval monks.  Philosopher Emanuel Kant refuted the argument, observing that the concept of existence does not constitute actual existence.

Irrelevant Premises
An irrelevant premise is one which, regardless of whether it is true or false, has no logical relationship to the point of the argument.

Fallacy

Description

Examples

Comments

appeal to belief

Implies that an idea is true because most people believe it.

"All Christendom knows the earth is flat, Señor Columbus!"

That many (or even all) people believe an idea doesn't make that idea true.

appeal to common practice

Asserts that something is correct or acceptable because "everyone" does it.

"Everyone cheats on their taxes, so there's nothing wrong with it."

The fact that a practice (slavery, for example) is widespread doesn't make it correct or  morally acceptable.

appeal to consequences of belief

Asserts that an idea is true, either because belief in it has desirable effects, or because lack of belief in it has undesirable effects.

"Nuclear war can't be possible.  If I believed it was, I'd be a nervous wreck."

The truth or falseness of ideas is seldom related to whether the consequences of believing them are desirable or undesirable.

appeals to emotion

appeal to fear or force (argumentum ad baculum): Threatens penalty for failure to agree.

"Professing the doctrine that the earth moves around the sun is punishable by torture."

Appeals to emotion may be positive (e.g., self-esteem) or negative (e.g., hatred of an out-group).

Other emotional appeals include indignation, loyalty, patriotism.

The general flaw of appeals to emotion is that truth is a function of reality, not of feelings, and certainly not of feelings about unrelated matters.  (In appeal to pity, for example, whether an applicant is inconvenienced by not being hired is not a matter of concern to the employer; the employer's concern is whether those he hires are competent, cooperative, productive, and honest.)

bandwagon: Carrot-and-stick variant of ad baculum offers inclusion as reward for agreeing, thus implies ostracism as penalty for disagreeing.

"If you go along with our plan, you'll be a respected member of the community."

appeal to flattery: Attempts to persuade by cajoling.

"That was a superb lecture, Professor.  By the way, could you give me full credit for the paper I turned in late?"

appeal to pity (argumentum ad misericordiam): Attempts to persuade by invoking sympathy.

"I can't support my family without this job, so you simply must hire me."

appeal to spite: Tries to justify a view or decision based on unrelated feelings of enmity or retribution.

"Susan didn't nominate me for treasurer, so despite her demonstrated ability and commitment to the club, I'm not voting for her for president."

appeal to popular opinion
(argumentum ad populum)

Implies that an idea is confirmed by popular acceptance.

"Even though police have sometimes resorted to brutal methods, the crackdown on crime is beneficial, since most people approve of the results."

That many people accept something does not make it correct or good.  Similar to appeals to belief, common practice, and emotion.  (Often equated with bandwagon fallacy.)

appeal to ridicule (argumentum ad ridiculam)

Substitutes ridicule or mockery of an idea for evidence against it.

"It's absurd to think that repealing laws against victimless crimes might restore respect for law and order!"

Mockery is not evidence, and ridicule is not reason.

arguments against the person
(argumentum ad hominem)

poisoning the well / abusive ad hominem: Attempts generally to discredit the arguer

"The witness is a prostitute, so her testimony about the burglary isn't credible."

Variants of ad hominem include abusive ad hominem (direct personal attack or "poisoning the well"), circumstantial ad hominem (charge of bias), and tu quoque (charge of hypocrisy).

charge of bias / circumstantial ad hominem: Attributes the arguer's viewpoint to a vested interest.

"Of course Jones criticizes our product. She's a stockholder of our competitor."

Although it's expected that a person might be influenced by prospects of personal gain or loss, this does not rule out that the person can be honest and objective.

charge of hypocrisy / tu quoque: Supposes the arguer is unqualified to espouse a view to which he himself has failed to adhere.

"Commissioner Smith is a fine one to talk about the importance of education, considering he didn't even finish 8th grade."

Inability to attain a certain goal does not mean that the goal is unworthy of being sought after.

false analogy

Attempts to draw a parallel between two functionally dissimilar situations.

"An audio amplifier magnifies electrical signals the way a lens magnifies light."

An audio amplifier does not magnify signals.  It's an active (powered) device that uses weak signals to control the output of a comparatively large power supply.  The passively refractive behavior of a lens is completely different.

red herring

Diverts attention from the issue in question.

"I can't be held responsible for the damage my dog caused, because there's no leash law in my neighborhood."

A red herring is often the mark of an inattentive arguer, but it can also be a deliberate attempt to divert attention, either from an opponent's line of reasoning, or from the weaknesses of one's own position.

straw man

Distorts an opposing viewpoint in such a way that the distortion is easily refuted.

"Evolution relies on random change. But it would be impossible for the human eye to assemble itself at random, so evolution can't be true."

Refuting a misrepresentation of a claim does not refute the actual claim itself.  (A straw man may be considered either an unwarranted assumption or an irrelevant premise, depending on whether the misrepresentation or its refutation, respectively, is interpreted as the essential flaw.)

Unwarranted Assumptions
An unwarranted assumption is either a premise that is poorly based or a conclusion that is inadequately supported.

Fallacy

Description

Examples

Comments

appeal to ignorance
(argumentum ad ignorantium)

Proposes that something must be true if not proved false, or false if not proved true.

"The existence of fairies has never been proved, so fairies don't exist."

"The existence of fairies has never been disproved, so fairies exist."

That something has never been observed or proved might give some grounds for bias against it, but by no means does it lead to a conclusion.  The futility of an appeal to ignorance is easily shown simply by standing it on its head, as our pair of examples illustrates.

appeal to novelty

Implies that something is better because it is new.  (Compare to appeal to tradition.)

"Buy new and improved Slosh detergent for a cleaner wash."

If what is "new" about Slosh turns out to be only that it uses cheaper ingredients to reduce costs, the alleged "improvement" will likely be confined to the manufacturer's profit margin.

appeal to tradition

Implies that something is better because it is old.  (Compare to appeal to novelty.)

"You can't possibly expect your new electric light to replace tried-and-true gaslight, Mr. Edison."

The mere fact that a thing or idea has endured for a long time does not mean it cannot be improved upon, or abandoned if it becomes obsolete.

appeal to unreliable authority
(argumentum ad verecundiam)

Attributes authority to a source whose expertise in the field in question is doubtful.

"Isaac Newton believed in astrology, so there must be something to it."

We don't cite the Pope as an authority on theoretical physics, just as we don't cite Hawking as an authority on Christian theology, though each is highly capable and respected in his own field of expertise.  Note that appeal to authority isn't fallacious when the authority is reliable; however, it isn't conclusive, because even credible authorities have been known to be biased or mistaken.

begging the question
(petitio principii) / circular reasoning

Uses some form of its own conclusion as one of its key premises.

"God's word is always true, the Bible is God's word, and the Bible says God exists. So God exists."

Sometimes the circularity is subtle, or even unstated but implied.

complex question

Asks a question with an unjustified presupposition.

"Have you stopped beating your wife yet?"

Although questions are not generally considered logical statements, the presupposition contained in a complex question constitutes a statement.

contradictory premises

Contains a self-contradictory premise, or two or more mutually exclusive premises.

"If God can do anything, he must be able to make a stone so heavy that he can't lift it."

Mutually contradictory premises cannot both be true at the same time and in the same way.

dubious generalizations

biased sample: Uses a skewed sample of individuals to draw conclusions about an entire group.

"A study taken in Florida and Maine shows 55% of the people spend much of their time near the ocean. So 55% of Americans spend much of their time near the ocean."

Unrepresentative samples yield unreliable conclusions.  (Compare to "spotlight.")

hasty generalization: Makes an unjustified general inference from an insufficient sample.

"The only two Italians I ever knew belonged to the Mafia. So if you ask me, all Italians are crooks."

There are millions of Italians. That the two individuals I happen to know are in the Mafia is not enough to generalize that all Italians are crooks—any more than it would justify a generalization that all the people I know are crooks.

spotlight: Infers that highly conspicuous individuals are typical of a group.

"On TV I saw a crowd of Palestinians chanting 'Death to Israel!' All Palestinians are murderous fiends."

Similar to "biased sample" fallacy.

unqualified generalization (dicto simpliciter): Makes an assumption about all individuals in a group, overlooking pertinent differences.

"Exercise is healthful, so everyone ought to exercise."

The example overlooks that, for people in poor health, exercise might be harmful or even fatal.

false or questionable causes

confusion of cause and effect: Misinterprets a causal relationship.

"The bread is going bad, so it's getting moldy."

Variants of false cause include confusion of cause and effect, post hoc ergo propter hoc ("after this, so because of this") and slippery slope fallacies.

post hoc ergo propter hoc (after this, so because of this): Assumes a causal relationship based on an observed sequence of events.

"John brought the layoff on himself by walking under a step-ladder."

Layoffs are caused by a need to reduce the number of employees, not by extraneous events.  (Post hoc ergo propter hoc is usually abbreviated to post hoc.

slippery slope: Supposes a specified event will inevitably generate a certain sequence of events. 

"Establishing equal rights for women will require men and women to share the same public rest rooms."

Slippery slope assumptions are warranted only if there's a high probability that the specified event will actually produce the anticipated sequence.

false choices

false dilemma: Sets unrealistic limits on possible options.

"Elizabeth must be either at home or at work."

The example ignores many possibilities for Elizabeth's whereabouts, such as at the shopping mall, at the theater, on vacation, visiting a friend, or in transit between locations.

false dichotomy / missing middle: Supposes options to be limited to two extremes, when in fact more moderate choices and compromises exist.

"Anyone who does not stand with us stands against us."

A special kind of false dilemma, in which there is a range of alternatives between two stated extremes, is called the "false dichotomy" or "missing middle" fallacy.

gambler's fallacy

Assumes the repeated occurrence of an event that departs from the expected norm indicates that the event will cease soon.

"I've lost $500 in this slot machine already, so it's bound to hit the jackpot any time now."

Events can be reliably predicted only when they (or other related and observable events) occur in some recognizable pattern or sequence.  Because random events exhibit no particular sequence, we can predict only their statistical chances, not specific occurrences.

genetic fallacy

Infers that information must be false if the reputation of its source is questionable.

"The way to tell when a politician is lying is that his lips are moving."

It is quite possible, even for sources that are frequently in error or even routinely dishonest, to make true statements.

guilt by association

Implies that an idea is bad if it is associated with harmful or unsavory ideas or practices.

"Religion is bad, because it's sometimes used to justify persecution, terrorism, and warfare."

Even the best of humanity's institutions have been used to excuse atrocities, and even the worst can give rise to some constructive ideas.

middle ground / golden mean

Assumes that a mean between two extreme alternatives must be the correct course.

"A storm blew my tree down onto my neighbor's shed, and he demands that I pay for it.  While I don't think I ought to pay, it should be fair if I pay him half of what he demands."

Although compromise is sometimes a realistic way to settle differences, in cases where the alternatives are justice and injustice, or truth and falsehood, a halfway measure is as devoid of justice and truth as the extreme.

non sequitur

Does not logically follow from the reasons presented.

"Marriage is traditionally a union of one man and one woman, so legitimizing homosexual unions would destroy traditional marriage."

A non sequitur misrepresents an unsupported or inadequately supported opinion as a conclusion.

relativist / subjectivist fallacy

Denies that what is objectively true for others is true for oneself.

"I read that geologists have dated some rocks at 200 million years. Maybe that's true for them, but it's not true for anyone who believes the Bible."

The relativist fallacy confuses opinion with reality, supposing that objective truth can vary from one person to another.

special pleading

Bids for exemption from standards assumed to apply to everyone else.

"You can't arresh me for drunk driving, offisher.  I'm a judge!"

Under some circumstances, special pleading is matter of adjusting balance and fairness.  But it can also be an unfair bid for special privilege or exemption from just obligation.

straw man

Distorts an opposing viewpoint in such a way that the distortion is easily refuted.

"Evolution relies on random change. But it would be impossible for the human eye to assemble itself at random, so evolution can't be true."

Refuting a misrepresentation of a claim does not refute the actual claim itself.  (A straw man may be considered either an unwarranted assumption or an irrelevant premise, depending on whether the misrepresentation or its refutation, respectively, is interpreted as the essential flaw.)

Formal Errors
A formal error is a violation of accepted rules of logical form and function.

Fallacy

Description

Examples

Comments

affirming a disjunct

Tries to deny one disjunct of a disjunction by affirming the other disjunct.

"You may have cream or sugar in your coffee.  Since you've chosen cream, you may not have sugar."

According to logical convention, a disjunction is considered inclusive (either one option or the other, or both) by default.  So, affirming one option does not exclude the other, unless the relationship is specified to be exclusive (either one option or the other, but not both).

Affirming a disjunct is a fallacious attempt to reverse the legitimate process of disjunctive syllogism, in which the denial of one disjunct confirms the other.

affirming the consequent

Tries to confirm the antecedent of a conditional statement from a true consequent.

"If it is raining, then the ground is wet. The ground is wet. So, it is raining."

We cannot conclude anything about the cause of wet ground, since there are things besides rain (e.g., dew, a natural spring, sprinklers, a burst water main) which can cause the ground to be wet.

denying the antecedent

Tries to refute the consequent of a conditional statement from a false antecedent.

"If it is raining, then the ground is wet. It is not raining. So, the ground is not wet.".

We cannot conclude anything about the results of no rain, since here are things besides rain (e.g., dew, a natural spring, sprinklers, a burst water main) which can cause the ground to be wet.

Two rules, modus ponens and modus tollens, govern the conditional IF relationship. In the symbolic example "If A, then B," A is the antecedent and B is the consequent.

• Modus ponens states that if A (the antecedent) is true, then B (the consequent) is necessarily true.
  But if A is false, that tells us nothing about B (except that if B happens to be true, it is for some reason other than A).

• Modus tollens states that if B (the consequent) is false, then A (the antecedent) is necessarily false.
  But if B is true, that tells us nothing about A (because there might well be other causes of B).

Note: In this example, the antecedent "it is raining" is the cause, and the consequent "the ground is wet" is the effect, though this is not always the case.  Consider another example, "If it is raining, then there are clouds in the sky;" in this case, the antecedent "it is raining" is the effect, and the consequent "there are clouds in the sky" is the cause.  There can even be situations in which neither antecedent nor consequent is either cause or effect, for instance, "If we have fish for dinner, then we drink white wine."  Regardless, the IF-THEN logic works exactly the same way with modus ponens and modus tollens—and malfunctions exactly the same way with either fallacy.

undistributed middle term

Fails to distribute the middle term of a syllogism with a universal (ALL or NO) quantifier.

"Some Arabs are wealthy.  My neighbors are Arabs.  So, my neighbors are wealthy."

We cannot conclude that the Arabs next door are wealthy merely because some Arabs are wealthy.  Some is an existential quantifier, not a universal quantifier.

The middle term of a categorical syllogism is the term that appears in both the major and minor premises.  In our example above, the middle term is "Arabs," which is not distributed in either premise with respect to all members of that category.  The formal fallacy of an undistributed middle term yields a non sequitur conclusion.

QUICK LIST | Irrelevant Premises | Unwarranted Assumptions | Ambiguities | Formal Errors

While this listing is more extensive and detailed than the basic lesson material, it's by no means complete.  Our interest here is to become acquainted with the most common kinds of fallacies that we're likely to encounter.  Taking the trouble to learn rare or obscure fallacies wouldn't be worth the effort for most readers, unless they aim to become lawyers or professional logicians.  (Latin terms are included for the benefit of those who use this page as an Internet reference.)

Additional fallacy descriptions can be found at many on-line sources, such as http://en.wikipedia.org/wiki/List_of_fallacies.