Fallacies of Distraction

False Dilemma: two choices are given when in fact there are three options

From Ignorance: because something is not known to be true, it is assumed to

be false

Slippery Slope: a series of increasingly unacceptable consequences is drawn

Complex Question: two unrelated points are conjoined as a single


Appeals to Motives in Place of Support

Appeal to Force: the reader is persuaded to agree by force

Appeal to Pity: the reader is persuaded to agree by sympathy

Consequences: the reader is warned of unacceptable consequences

Prejudicial Language: value or moral goodness is attached to believing the


Popularity: a proposition is argued to be true because it is widely held to be


Changing the Subject

Attacking the Person:

(1) the person's character is attacked

(2) the person's circumstances are noted

(3) the person does not practise what is preached

Appeal to Authority:

(1) the authority is not an expert in the field

(2) experts in the field disagree

(3) the authority was joking, drunk, or in some other way not being


Anonymous Authority: the authority in question is not named

Style Over Substance: the manner in which an argument (or arguer) is

presented is felt to affect the truth of the conclusion

Inductive Fallacies

Hasty Generalization: the sample is too small to support an inductive

generalization about a population

Unrepresentative Sample: the sample is unrepresentative of the sample as a whole

False Analogy: the two objects or events being compared are relevantly


Slothful Induction: the conclusion of a strong inductive argument is denied

despite the evidence to the contrary

Fallacy of Exclusion: evidence which would change the outcome of an

inductive argument is excluded from consideration

Fallacies Involving Statistical Syllogisms

Accident: a generalization is applied when circumstances suggest that there

should be an exception

Converse Accident : an exception is applied in circumstances where a

generalization should apply

Causal Fallacies

Post Hoc: because one thing follows another, it is held to be caused by the


Joint effect: one thing is held to cause another when in fact they are both the

joint effects of an underlying cause

Insignificant: one thing is held to cause another, and it does, but it is

insignificant compared to other causes of the effect

Wrong Direction: the direction between cause and effect is reversed

Complex Cause: the cause identified is only a part of the entire cause of the


Missing the Point

Begging the Question: the truth of the conclusion is assumed by the premises

Irrelevant Conclusion: an argument in defense of one conclusion instead

proves a different conclusion

Straw Man: the author attacks an argument different from (and weaker than)

the opposition's best argument

Fallacies of Ambiguity

Equivocation: the same term is used with two different meanings

Amphiboly: the structure of a sentence allows two different interpretations

Accent: the emphasis on a word or phrase suggests a meaning contrary to

what the sentence actually says

Category Errors

Composition: because the attributes of the parts of a whole have a certain

property, it is argued that the whole has that property

Division: because the whole has a certain property, it is argued that the parts

have that property

Non Sequitur

Affirming the Consequent: any argument of the form: If A then B, B,

therefore A

Denying the Antecedent: any argument of the form: If A then B, Not A, thus

Not B

Inconsistency: asserting that contrary or contradictory statements are both


Syllogistic Errors

Fallacy of Four Terms: a syllogism has four terms

Undistributed Middle: two separate categories are said to be connected

because they share a common property

Illicit Major: the predicate of the conclusion talks about all of something, but

the premises only mention some cases of the term in the predicate

Illicit Minor: the subject of the conclusion talks about all of something, but

the premises only mention some cases of the term in the subject

Fallacy of Exclusive Premises: a syllogism has two negative premises

Fallacy of Drawing an Affirmative Conclusion From a Negative Premise: as

the name implies

Existential Fallacy: a particular conclusion is drawn from universal premises

Fallacies of Explanation

Subverted Support (The phenomenon being explained doesn't exist)

Non-support (Evidence for the phenomenon being explained is biased)

Untestability (The theory which explains cannot be tested)

Limited Scope (The theory which explains can only explain one thing)

Limited Depth (The theory which explains does not appeal to underlying


Fallacies of Definition

Too Broad (The definition includes items which should not be included)

Too Narrow (The definition does not include all the items which shouls be


Failure to Elucidate (The definition is more difficult to understand than the

word or concept being defined)

Circular Definition (The definition includes the term being defined as a part of

the definition)

Conflicting Conditions (The definition is self-contradictory)


For Educators... Please feel free to download the entire text (50 K) in

plain-brown wrapper HTML (does not contain the last three sections - sorry). The

text version is also covered by copyright. 13 August 1996

Stephen's Guide to the Logical Fallacies



The point of an argument is to give reasons in support of some

conclusion. An argument commits a fallacy when the reasons offered do not, in

fact, support the conclusion.

Each fallacy is described in the following format:

Name: this is the generally accepted name of the fallacy

Definition: the fallacy is defined

Examples: examples of the fallacy are given

Proof: the steps needed to prove that the fallacy is committed

Note: Please keep in mind that this is a work in progress, and therefore should not

be thought of as complete in any way.

Fallacies of Distraction


Each of these fallacies is characterized by the illegitimate use of a logical operator

in order to distract the reader from the apparent falsity of a certain proposition.

False Dilemma

Definition: A limited number of options (usually two) is given, while in

reality there are more options. A false dilemma is an

illegitimate use of the "or" operator.

Examples: (i) Either you're for me or against me.

(ii) America: love it or leave it.

(iii) Either support Meech Lake or Quebec will separate.

Proof: Identify the options given and show (with an example) that

there is an additional option.

(Cedarblom and Paulsen: 136)

Argument From Ignorance( argumentum ad ignorantiam )

Definition: Arguments of this form assume that since something has not

been proven false, it is therefore true. Conversely, such an

argument may assume that since something has not been

proven true, it is therefore false. (This is a special case of a

false dilemma, since it assumes that all propositions must

ether be known to be true or known to be false.)

As Davis writes, "Lack of proof is not proof." (p. 59)

Examples: (i) Since you cannot prove that ghosts do not exist, they must


(ii) Since scientists cannot prove that global warming will

occur, it probably won't.

(iii) Fred said that he is smarter than Jill, but he didn't

prove it, so it must be false.

Proof: Identify the proposition in question. Argue that it may be true

even though we don't know whether it is or isn't.

(Copi and Cohen: 93, Davis: 59)

Slippery Slope

Definition: In order to show that a proposition P is unacceptable, a

sequence of increasingly unacceptable events is shown to

follow from P. A slippery slope is an illegitimate use of the"if-

then" operator.

Examples: (i) If we pass laws against fully-automatic weapons, then it

won't be long before we pass laws on all weapons, and then

we will begin to restrict other rights, and finally we will end

up living in a communist state. Thus, we should not ban

fully-automatic weapons.

(ii) You should never gamble. Once you start gambling you

find it hard to stop. Soon you are spending all your money

on gambling, and eventually you will turn to crime to

support your earnings.

(iii) If I make an exception for you then I have to make an

exception for everyone.

Proof: Identify the proposition P being refuted and identify the final

event in the series of events. Then show that this final event

need not occur as a consequence of P.

(Cedarblom and Paulsen: 137)

Complex Question

Definition: Two otherwise unrelated points are conjoined and treated as

a single proposition. The reader is expected to accept or

reject both together, when in reality one is acceptable while

the other is not. A complex question is an illegitimate use of

the "and" operator.

Examples: (i) You should support home education and the God-given

right of parents to raise their children according to their

own beliefs.

(ii) Do you support freedom and the right to bear arms?

(iii) Have you stopped using illegal sales practises? (This asks

two questions: did you use illegal practises, and did you


Proof: Identify the two propositions illegitimately conjoined and

show that believing one does not mean that you have to

believe the other.

(Cedarblom and Paulsen: 86, Copi and Cohen: 96)

Appeals to Motives in Place of Support


The fallacies in this section have in common the practise of appealing to emotions

or other psychological factors. In this way, they do not provide reasons for belief.

Appeal to Force ( argumentum ad baculum )

Definition: The reader is told that unpleasant consequences will follow

if they do not agree with the author.

Examples: (i) You had better agree that the new company policy is the

best bet if you expect to keep your job.

(ii) NAFTA is wrong, and if you don't vote against NAFTA

then we will vote you out of office.

Proof: Identify the threat and the proposition and argue that the

threat is unrelated to the truth or falsity of the proposition.

(Cedarblom and Paulsen: 151, Copi and Cohen: 103)

Appeal to Pity( argumentum ad misercordiam )

Definition: The reader is told to agree to the proposition because of the

pitiful state of the author.

Examples: (i) How can you say that's out? It was so close, and besides,

I'm down ten games to two.

(ii) We hope you'll accept our recommendations. We spent

the last three months working extra time on it.

Proof: Identify the proposition and the appeal to pity and argue that

the pitiful state of the arguer has nothing to do with the truth

of the proposition.

(Cedarblom and Paulsen: 151, Copi and Cohen: 103, Davis: 82)

Appeal to Consequences( argumentum ad consequentiam )

Definition: The author points to the disagreeable consequences of

holding a particular belief in order to show that this belief is


Example: (i) You can't agree that evolution is true, because if it were,

then we would be no better than monkeys and apes.

(ii) You must believe in God, for otherwise life would have

no meaning. (Perhaps, but it is equally possible that since

life has no meaning that God does not exist.)

Proof: Identify the consequences to and argue that what we want to

be the case does not affect what is in fact the case.

(Cedarblom and Paulsen: 100, Davis: 63)

Prejudicial Language

Definition: Loaded or emotive terms are used to attach value or moral

goodness to believing the proposition.

Examples: (i) Right thinking Canadians will agree with me that we

should have another free vote on capital punishment.

(ii) A reasonable person would agree that our income

statement is too low.

(iii) Senator Turner claims that the new tax rate will reduce

the deficit. (Here, the use of "claims" implies that what

Turner says is false.)

(iv) The proposal is likely to be resisted by the bureaucrats

on Parliament Hill. (Compare this to: The proposal is likely

to be rejected by officials on Parliament Hill.)

Proof: Identify the prejudicial terms used (eg. "Right thinking

Canadians" or "A reasonable person"). Show that disagreeing

with the conclusion does not make a person "wrong thinking"

or "unreasonable".

(Cedarblom and Paulsen: 153, Davis: 62)

Appeal to Popularity( argumentum ad populum )

Definition: A proposition is held to be true because it is widely held to

be true or is held to be true by some (usually upper crust)

sector of the population.

This fallacy is sometimes also called the "Appeal to Emotion"

because emotional appeals often sway the population as a


Examples: (i) If you were beautiful, you could live like this, so buy

Buty-EZ and become beautiful. (Here, the appeal is to the

"beautiful people".)

(ii) Polls suggest that the Liberals will form a majority

government, so you may as well vote for them.

(iii) Everyone knows that the Earth is flat, so why do you

persist in your outlandish claims?

(Copi and Cohen: 103, Davis: 62)

Changing the Subject


The fallacies in this section change the subject by discussing the person making

the argument instead of discussing reasons to believe or disbelieve the conclusion.

While on some occasions it is useful to cite authorities, it is almost never

appropriate to discuss the person instead of the argument.

Attacking the Person ( argumentum ad hominem )

Definition: The person presenting an argument is attacked instead of the

argument itself. This takes many forms. For example, the

person's character, nationality or religion may be attacked.

Alternatively, it may be pointed out that a person stands to

gain from a favourable outcome. Or, finally, a person may be

attacked by association, or by the company he keeps.

There are three major forms of Attacking the Person:

(1) ad hominem (abusive): instead of attacking an assertion,

the argument attacks the person who made the assertion.

(2) ad hominem (circumstantial): instead of attacking an

assertion the author points to the relationship between the

person making the assertion and the person's circumstances.

(3) ad hominem (tu quoque): this form of attack on the

person notes that a person does not practise what he


Examples: (i) You may argue that God doesn't exist, but you are just

following a fad. (ad hominem abusive)

(ii) We should discount what Premier Klein says about

taxation because he won't be hurt by the increase. (ad

hominem circumstantial)

(iii) We should disregard Share B.C.'s argument because they

are being funded by the logging industry. (ad hominem


(iv) You say I shouldn't drink, but you haven't been sober for

more than a year. (ad hominem tu quoque)

Proof: Identify the attack and show that the character or

circumstances of the person has nothing to do with the truth

or falsity of the proposition being defended.

(Barker: 166, Cedarblom and Paulsen: 155, Copi and Cohen: 97, Davis: 80)

Appeal to Authority( argumentum ad verecundiam )

Definition: While sometimes it may be appropriate to cite an authority to

support a point, often it is not. In particular, an appeal to

authority is inappropriate if:

(i) the person is not qualified to have an expert

opinion on the subject,

(ii) experts in the field disagree on this issue.

(iii) the authority was making a joke, drunk, or

otherwise not being serious

A variation of the fallacious appeal to authority is hearsay. An

argument from hearsay is an argument which depends on

second or third hand sources.

Examples: (i) Noted psychologist Dr. Frasier Crane recommends that

you buy the EZ-Rest Hot Tub.

(ii) Economist John Kenneth Galbraith argues that a tight

money policy s the best cure for a recession. (Although

Galbraith is an expert, not all economists agree on this


(iii) We are headed for nuclear war. Last week Ronald

Reagan remarked that we begin bombing Russia in five

minutes. (Of course, he said it as a joke during a

microphone test.)

(iv) My friend heard on the news the other day that Canada

will declare war on Serbia. (This is a case of hearsay; in

fact, the reporter said that Canada would not declare war.)

(v) The Ottawa Citizen reported that sales were up 5.9

percent this year. (This is hearsay; we are not n a position to

check the Citizen's sources.)

Proof: Show that either (i) the person cited is not an authority in the

field, or that (ii) there is general disagreement among the

experts in the field on this point.

(Cedarblom and Paulsen: 155, Copi and Cohen: 95, Davis: 69)

Anonymous Authorities

Definition: The authority in question is not named. This is a type of

appeal to authority because when an authority is not named

it is impossible to confirm that the authority is an expert.

However the fallacy is so common it deserves special


A variation on this fallacy is the appeal to rumour. Because

the source of a rumour is typically not known, it is not

possible to determine whether to believe the rumour. Very

often false and harmful rumours are deliberately started n

order to discredit an opponent.

Examples: (i) A government official said today that the new gun law

will be proposed tomorrow.

(ii) Experts agree that the best way to prevent nuclear war

is to prepare for it.

(iii) It is held that there are more than two million needless

operations conducted every year.

(iv) Rumour has it that the Prime Minster will declare

another holiday in October.

Proof: Argue that because we don't know the source of the

information we have no way to evaluate the reliability of the


(Davis: 73)

Style Over Substance

Definition: The manner in which an argument (or arguer) is presented is

taken to affect the likelihood that the conclusion is true.

Examples: (i) Nixon lost the presidential debate because of the sweat on

his forehead.

(ii) Trudeau knows how to move a crowd. He must be right.

(iii) Why don't you take the advice of that nicely dressed

young man?

Proof: While it is true that the manner in which an argument is

presented will affect whether people believe that its

conclusion is true, nonetheless, the truth of the conclusion

does not depend on the manner in which the argument is

presented. In order to show that this fallacy is being

committed, show that the style in this case does not affect the

truth or falsity of the conclusion.

(Davis: 61)

Inductive Fallacies


Inductive reasoning consists on inferring from the properties of a sample to the

properties of a population as a whole.

For example, suppose we have a barrel containing of 1,000 beans. Some of the

beans are black and some of the beans are white. Suppose now we take a sample

of 100 beans from the barrel and that 50 of them are white and 50 of them are

black. Then we could infer inductively that half the beans in the barrel (that is,

500 of them) are black and half are white.

All inductive reasoning depends on the similarity of the sample and the

population. The more similar the same is to the population as a whole, the more

reliable will be the inductive inference. On the other hand, if the sample is

relevantly dissimilar to the population, then the inductive inference will be


No inductive inference is perfect. That means that any inductive inference can

sometimes fail. Even though the premises are true, the conclusion might be false.

Nonetheless, a good inductive inference gives us a reason to believe that the

conclusion is probably true.

Hasty Generalization

Definition: The size of the sample is too small to support the conclusion.

Examples: (i) Fred, the Australian, stole my wallet. Thus, all Australians

are thieves. (Of course, we shouldn't judge all Australians on

the basis of one example.)

(ii) I asked six of my friends what they thought of the new

spending restraints and they agreed it is a good idea. The

new restraints are therefore generally popular.

Proof: Identify the size of the sample and the size of the population,

then show that the sample size is too small. Note: a formal

proof would require a mathematical calculation. This is the

subject of probability theory. For now, you must rely on

common sense.

(Barker: 189, Cedarblom and Paulsen: 372, Davis: 103)

Unrepresentative Sample

Definition: The sample used in an inductive inference is relevantly

different from the population as a whole.

Examples: (i) To see how Canadians will vote in the next election we

polled a hundred people in Calgary. This shows conclusively

that the Reform Party will sweep the polls. (People in

Calgary tend to be more conservative, and hence more likely

to vote Reform, than people in the rest of the country.)

(ii) The apples on the top of the box look good. The entire

box of apples must be good. (Of course, the rotten apples are

hidden beneath the surface.)

Proof: Show how the sample is relevantly different from the

population as a whole, then show that because the sample is

different, the conclusion is probably different.

(Barker: 188, Cedarblom and Paulsen: 226, Davis: 106)

False Analogy

Definition: In an analogy, two objects (or events), A and B are shown to

be similar. Then it is argued that since A has property P, so

also B must have property P. An analogy fails when the two

objects, A and B, are different in a way which affects whether

they both have property P.

Examples: (i) Employees are like nails. Just as nails must be hit in the

head in order to make them work, so must employees.

(ii) Government is like business, so just as business must be

sensitive primarily to the bottom line, so also must

government. (But the objectives of government and business

are completely different, so probably they will have to meet

different criteria.)

Proof: Identify the two objects or events being compared and the

property which both are said to possess. Show that the two

objects are different in a way which will affect whether they

both have that property.

(Barker: 192, Cedarblom and Paulsen: 257, Davis: 84)

Slothful Induction

Definition: The proper conclusion of an inductive argument is denied

despite the evidence to the contrary.

Examples: (i) Hugo has had twelve accidents n the last six months, yet

he insists that it is just a coincidence and not his fault.

(Inductively, the evidence is overwhelming that it is his fault.

This example borrowed from Barker, p. 189)

(ii) Poll after poll shows that the N.D.P will win fewer than

ten seats in Parliament. Yet the party leader insists that the

party is doing much better than the polls suggest. (The N.D.P.

in fact got nine seats.)

Proof: About all you can do in such a case is to point to the strength

of the inference.

(Barker: 189)

Fallacy of Exclusion

Definition: Important evidence which would undermine an inductive

argument is excluded from consideration. The requirement

that all relevant information be included is called the

"principle of total evidence".

Examples: (i) Jones is Albertan, and most Albertans vote Tory, so Jones

will probably vote Tory. (The information left out is that

Jones lives in Edmonton, and that most people in Edmonton

vote Liberal or N.D.P.)

(ii) The Leafs will probably win this game because they've

won nine out of their last ten. (Eight of the Leafs' wins came

over last place teams, and today they are playing the first

place team.)

Proof: Give the missing evidence and show that it changes the

outcome of the inductive argument. Note that it is not

sufficient simply to show that not all of the evidence was

included; it must be shown that the missing evidence will

change the conclusion.

(Davis: 115)

Fallacies Involving Statistical Syllogisms


A statistical generalization is a statement which is usually true, but not always

true. Very often these are expressed using the word "most", as in "Most

conservatives favour welfare cuts." Sometimes the word "generally" s used, as in

"Conservatives generally favour welfare cuts." Or, sometimes, no specific word is

used at all, as in: "Conservatives favour welfare cuts."

Fallacies involving statistical generalizations occur because the generalization is not

always true. Thus, when an author treats a statistical generalization as though it

were always true, the author commits a fallacy.


Definition: A general rule is applied when circumstances suggest that an

exception to the rule should apply.

Examples: (i) The law says that you should not travel faster than 50

kph, thus even though your father could not breathe, you

should not have travelled faster than 50 kph.

(ii) It is good to return things you have borrowed. Therefore,

you should return this automatic rifle from the madman you

borrowed it from. (Adapted from Plato's Republic, Book I).

Proof: Identify the generalization in question and show that it s not

a universal generalization. Then show that the circumstances

of this case suggest that the generalization ought not to apply.

(Copi and Cohen: 100)

Converse Accident

Definition: An exception to a generalization is applied to cases where the

generalization should apply.

Examples: (i) Because we allow terminally ill patients to use heroin, we

should allow everyone to use heroin.

(ii) Because you allowed Jill, who was hit by a truck, to

hand in her assignment late, you should allow the entire

class to hand in their assignments late.

Proof: Identify the generalization in question and show how the

special case was an exception to the generalization.

(Copi and Cohen: 100)

Causal Fallacies


It is common for arguments to conclude that one thing causes another. But the

relation between cause and effect is a complex one. It is easy to make a mistake.

In general, we say that a cause C is the cause of an effect E if and only if:

(i) Generally, if C occurs, then E will occur, and

(ii) Generally, if C does not occur, then E will not occur ether.

We say "generally" because there are always exceptions. For example:

We say that striking the match causes the match to light, because:

(i) Generally, when the match is struck, it lights (except when the match

is dunked in water), and

(ii) Generally, when the match is not struck, it does not light (except when

it is lit with a blowtorch).

Many writers also require that a causal statement be supported with a natural law.

For example, the statement that "striking the match causes it to light" is supported

by the principle that "friction produces heat, and heat produces fire".

Coincidental Correlation ( post hoc ergo prompter hoc )

Definition: The name in Latin means "after this therefore because of this".

This describes the fallacy. An author commits the fallacy when

it is assumed that because one thing follows another that the

one thing was caused by the other.

Examples: (i) Immigration to Alberta from Ontario increased. Soon

after, the welfare rolls increased. Therefore, the increased

immigration caused the increased welfare rolls.

(ii) I took EZ-No-Cold, and two days later, my cold


Proof: Show that the correlation is coincidental by showing that: (i)

the effect would have occurred even if the cause did not

occur, or (ii) that the effect was caused by something other

than the suggested cause.

(Cedarblom and Paulsen: 237, Copi and Cohen: 101)

Joint Effect

Definition: One thing is held to cause another when in fact both are the

effect of a single underlying cause. This fallacy is often

understood as a special case of post hoc ergo prompter hoc.

Examples: (i) We are experiencing high unemployment which s being

caused by a low consumer demand. (In fact, both may be

caused by high interest rates.)

(ii) You have a fever and this is causing you to break out in

spots. (In fact, both symptoms are caused by the measles.)

Proof: Identify the two effects and show that they are caused by the

same underlying cause. It is necessary to describe the

underlying cause and prove that it causes each symptom.

(Cedarblom and Paulsen: 238)

Genuine but Insignificant Cause

Definition: The object or event identified as the cause of an effect is a

genuine cause, but insignificant when compared to the other

causes of that event.

Note that this fallacy does not apply when all other

contributing causes are equally insignificant. Thus, it is not a

fallacy to say that you helped cause defeat the Tory

government because you voted Reform, for your vote had as

much weight as any other vote, and hence is equally a part of

the cause.

Examples: (i) Smoking is causing air pollution in Edmonton. (True, but

the effect of smoking is insignificant compared to the effect

of auto exhaust.)

(ii) By leaving your oven on overnight you are contributing

to global warming.

Proof: Identify the much more significant cause.

(Cedarblom and Paulsen: 238)

Wrong Direction

Definition: The relation between cause and effect is reversed.

Examples: (i) Cancer causes smoking.

(ii) The increase in AIDS was caused by more sex education.

(In fact, the increase in sex education was caused by the

spread of AIDS.)

Proof: Give a causal argument showing that the relation between

cause and effect has been reversed.

(Cedarblom and Paulsen: 238)

Complex Cause

Definition: The effect is caused by a number of objects or events, of

which the cause identified is only a part. A variation of this is

the feedback loop where the effect is itself a part of the cause.

Examples: (i) The accident was caused by the poor location of the bush.

(True, but it wouldn't have occurred had the driver not been

drunk and the pedestrian not been jaywalking.)

(ii) The Challenger explosion was caused by the cold

weather. (True, however, it would not have occurred had the

O-rings been properly constructed.)

(iii) People are in fear because of increased crime. (True, but

this has lead people to break the law as a consequence of

their fear, which increases crime even more.)

Proof: Show that all of the causes, and not just the one mentioned,

are required to produce the effect.

)Cedarblom and Paulsen: 238)

Missing the Point


These fallacies have in common a general failure to prove that the conclusion is


Begging the Question ( petitio principii )

Definition: The truth of the conclusion is assumed by the premises.

Often, the conclusion is simply restated in the premises in a

slightly different form. In more difficult cases, the premise is

a consequence of the conclusion.

Examples: (i) Since I'm not lying, it follows that I'm telling the truth.

(ii) We know that God exists, since the Bible says God exists.

What the Bible says must be true, since God wrote it and

God never lies. (Here, we must agree that God exists in order

to believe that God wrote the Bible.)

Proof: Show that in order to believe that the premises are true we

must already agree that the conclusion is true.

(Barker: 159, Cedarblom and Paulsen: 144, Copi and Cohen: 102, Davis: 33)

Irrelevant Conclusion ( ignoratio elenchi )

Definition: An argument which purports to prove one thing instead

proves a different conclusion.

Examples: (i) You should support the new housing bill. We can't

continue to see people living in the streets; we must have

cheaper housing. (We may agree that housing s important

even though we disagree with the housing bill.)

(ii) I say we should support affirmative action. White males

have run the country for 500 years. They run most of

government and industry today. You can't deny that this

sort of discrimination is intolerable. (The author has proven

that there is discrimination, but not that affirmative action

will end that discrimination.)

Proof: Show that the conclusion proved by the author is not the

conclusion that the author set out to prove.

(Copi and Cohen: 105)

Straw Man

Definition: The author attacks an argument which is different from, and

usually weaker than, the opposition's best argument.

Examples: (i) People who opposed the Charlottown Accord probably just

wanted Quebec to separate. But we want Quebec to stay in


(ii) We should have conscription. People don't want to enter

the military because they find it an inconvenience. But they

should realize that there are more important things than


Proof: Show that the opposition's argument has been

misrepresented by showing that the opposition has a stronger

argument. Describe the stronger argument.

(Cedarblom and Paulsen: 138)

Fallacies of Ambiguity


The fallacies in this section are all cases where a word or phrase is used unclearly.

There are two ways in which this can occur.

(i) The word or phrase may be ambiguous, in which case it has more than

one distinct meaning.

(ii) The word or phrase may be vague, in which case it has no distinct



Definition: The same word is used with two different meanings.

Examples: (i) Criminal actions are illegal, and all murder trials are

criminal actions, thus all murder trials are illegal. (Here the

term "criminal actions" is used with two different meanings.

Example borrowed from Copi.)

(ii) The sign said "fine for parking here", and since it was

fine, I parked there.

(iii) All child-murderers are inhuman, thus, no child-

murderer is human. (From Barker, p. 164; this is called

"illicit obversion")

(iv) A plane is a carpenter's tool, and the Boeing 737 is a

place, hence the Boeing 737 is a carpenter's tool. (Example

borrowed from Davis, p. 58)

Proof: Identify the word which is used twice, then show that a

definition which is appropriate for one use of the word would

not be appropriate for the second use.

(Barker: 163, Cedarblom and Paulsen: 142, Copi and Cohen: 113, Davis: 58)


Definition: An amphiboly occurs when the construction of a sentence

allows it to have two different meanings.

Examples: (i) Last night I shot a burglar in my pyjamas.

(ii) The Oracle of Delphi told Croseus that if he pursued the

war he would destroy a mighty kingdom. (What the Oracle

did not mention was that the kingdom he destroyed would

be his own. Adapted from Heroditus, The Histories.)

(iii) Save soap and waste paper. (From Copi, p. 115)

Proof: Identify the ambiguous phrase and show the two possible


(Copi and Cohen: 114)


Definition: Emphasis is used to suggest a meaning different from the

actual content of the proposition.

Examples: (i) It would be illegal to give away

Free Beer!

(ii) The first mate, seeking revenge on the captain, wrote in

his journal, "The Captain was sober today." (He suggests, by

his emphasis, that the Captain is usually drunk. From Copi,

p. 117)

(Copi and Cohen: 115)

Category Errors


These fallacies occur because the author mistakenly assumes that the whole is

nothing more than the sum of its parts. However, things joined together may have

different properties as a whole than any of them do separately.


Definition Because the parts of a whole have a certain property, it is argued

that the whole has that property. That whole may be either an object

composed of different parts, or it may be a collection or set of

individual members.

Examples: (i) The brick wall is six feet tall. Thus, the bricks in the wall are six

feet tall.

(ii) Germany is a militant country. Thus, each German is militant.

(iii) Conventional bombs did more damage in W.W. II than nuclear

bombs. Thus, a conventional bomb is more dangerous than a

nuclear bomb. (From Copi, p. 118)

Proof: Show that the properties in question are the properties of the whole,

and not of each part or member or the whole. If necessary, describe

the parts to show that they could not have the properties of the


(Barker: 164, Copi and Cohen: 117)


Definition: Because the whole has a certain property, it is argued that the parts

have that property. The whole in question may be either a whole

object or a collection or set of individual members.

Examples: (i) Each brick is three inches high, thus, the brick wall is three

inches high.

(ii) Because the brain is capable of consciousness, each neural cell

in the brain must be capable of consciousness.

Proof: Show that the properties in question are the properties of the parts,

and not of the whole. If necessary, describe the parts to show that

they could not have the properties of the whole.

(Barker: 164, Copi and Cohen: 119)



The term non sequitur literally means "it does not follow". In this section we

describe fallacies which occur as a consequence of invalid arguments.

Affirming the Consequent

Definition: Any argument of the following form is invalid:

If A then B


Therefore, A

Examples: (i) If I am in Calgary, then I am in Alberta. I am in Alberta,

thus, I am in Calgary. (Of course, even though the premises

are true, I might be in Edmonton, Alberta.)

(ii) If the mill were polluting the river then we would see an

increase in fish deaths. And fish deaths have increased. Thus,

the mill is polluting the river.

Proof: Show that even though the premises are true, the conclusion

could be false. In general, show that B might be a

consequence of something other than A. For example, the fish

deaths might be caused by pesticide run-off, and not the mill.

(Barker: 69, Cedarblom and Paulsen: 24, Copi and Cohen: 241)

Denying the Antecedent

Definition: Any argument of the following form is invalid:

If A then B

Not A

Therefore, Not B

Examples: (i) If you get hit by a car when you are six then you will die

young. But you were not hit by a car when you were six.

Thus you will not die young. (Of course, you could be hit by

a train at age seven.)

(ii) If I am in Calgary then I am in Alberta. I am not in

Calgary, thus, I am not in Alberta.

Proof: Show that even though the premises are true, the conclusion

may be false. In particular, show that the consequence B may

occur even though A does not occur.

(Barker: 69, Cedarblom and Paulsen: 26, Copi and Cohen: 241)


Definition: The author asserts more than one proposition such that the

propositions cannot all be true. In such a case, the

propositions may be contradictories or they may be


Examples: (i) Montreal is about 200 km from Ottawa, while Toronto is

400 km from Ottawa. Toronto is closer to Ottawa than


(ii) John is taller than Jake, and Jake is taller than Fred,

while Fred is taller than John.

Proof: Assume that one of the statements is true, and then use it as

a premise to show that one of the other statements is false.

(Barker: 157)