Stephen Downes' Guide to the Logical Fallacies
(Also published on the Internet as "Brian Yoder's Fallacy Zoo")
Fallacies of Distraction
Appeals to Motives in Place of Support
Changing the Subject
Fallacies Involving Statistical Syllogisms
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. The following fallacies are fallacies of distraction:
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"
(i) Either you're for me or against me.
(ii) America: love it or leave it.
(iii) Either support gun confiscation or have the government provide
everyone with his own private nuclear warhead, you decide which one.
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)
Arguments of this form assume that since something has not been proven
false (or cannot be), 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 either be known to be true or known to be false.)
As Davis writes, "Lack of proof is not proof." (p. 59)
(i) Since you cannot prove that ghosts do not exist, therefore they
(ii) Since scientists have not proven that global warming will occur,
therefore it won't.
(iii) Fred said that he is smarter than Jill, but he didn't prove it,
so it must be false.
Identify the proposition in question. Argue without evidence and proof
no claims whatsoever can be derived on the subject. Such a claim is neither
true nor false, but arbitrary.
Copi and Cohen: 93; Davis: 59; Rand: 79
In order to show that a proposition is unacceptable, a sequence of
increasingly unacceptable events is claimed to follow from it. A slippery
slope is an illegitimate compositing of the"if- then" operator. Of course
this ought to be distinguished from pointing out a chain of causal consequences
from a choice or position. The difference is that in a slippery slope fallacy
the intermediate causal connections are unproven.
(i) If we pass laws against private nuclear weapons, then it won't
be long before we pass laws against guns, 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 private nuclear 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
Identify the proposition being refuted and identify the final event
in the series of events. Then show that this final event need not occur
consequence of the proposition.
Cedarblom and Paulsen: 137
Two otherwise unrelated points are treated as a single proposition.
The reader is expected to accept or reject both together, when in reality
one may be acceptable while the other is not. A complex question is an
illegitimate use of the "and" operator.
(i) You should support home schooling and the God-given right of parents
to raise their children according to their own beliefs. (Whether parents
have a right to choose how to raise their children and whether that right
includes home schooling is an entirely different issue. There is an additional
complex question here since one might believe that a certain right exists
but not believe it comes from God.)
(ii) Do you support freedom and the right to bear arms? (What if I
think people ought to be free to bear arms but that it isn't a right? What
if I think it is a right, but I don't think it matters what rights people
(iii) Have you stopped beating your wife? (This implicitly asks two
questions: did you beat your wife, and did you stop?)
Identify the two propositions illegitimately conjoined and show that
one doen't imply 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 practice of appealing
to emotions or other psychological factors. In this way, they do not provide
reasons for belief, but merely "trick" people into agreeing with them one
way or another without proof.
The following fallacies are appeals to motive in place of support:
Appeal to Force (argumentum ad baculum)
The reader is threatened with unpleasant consequences if they do not
agree with the author.
(i) You had better agree that the new company policy is the best if
you expect to keep your job.
(ii) You had better admit that racism is wrong or one day you might
just find out how much you care about your wife and kids.
(iii) The defendant ought to be found innocent because if he isn't,
there will be a riot and many innocent citizens will be hurt or killed.
(iv) Accept Jesus as your savior or face the rack and branding irons!
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)
The reader is told to agree to the proposition because of the pitiful
state of the author.
(i) How can you say that ball was out of bounds? It was so close, and
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 and we are quite exhausted.
(iii) You ought to think highly of my term paper especially since I
graduated last in my class.
(iv) You ALWAYS win these arguments. Can't you let me win just this
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)
The author points to the disagreeable consequences of holding a particular
belief in order to show that this belief is false.
(i) You can't agree that evolution is true, because if it were, then
we would be no better than the apes.
(ii) You must believe in God, otherwise life would have no meaning.
(iii) I could never agree that smoking is harmful because if I did
I would have to stop.
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
Loaded or emotive terms are used to attach value or moral goodness
to believing the proposition or suspicion or dislike to the opposing position.
(i) Right thinking Californians will agree with me that we should have
another free vote on capital punishment.
(ii) Not only is paying a higher income tax a patriotic duty, it is
also a sacred obligation.
(iii) Senator Jones "claims" that the new tax rate will reduce the
deficit. (The use of "claims" implies that what Jones says is false.)
(iv) The proposal is likely to be resisted by the bureaucrats on Capitol
Hill. (Compare this to: The proposal is likely to be rejected by officials
on Capitol Hill.)
Identify the prejudicial terms used (eg. "Right thinking Californians"
or "sacred obligation"). Show that disagreeing with the conclusion does
not make a person "wrong thinking" or "irresponsible" unless some independent
proof can be offered. If they can't they are just _begging the question_.
Cedarblom and Paulsen: 153, Davis: 62
Appeal to Popularity (argumentum ad populum)
A proposition is held to be true because it is widely held to be true
or is held to be true by some (usually superior) sector of the population.
This fallacy is sometimes also called the "Appeal to Emotion" because
emotional appeals often sway the population as a whole.
(i) Everyone likes beautiful people, so buy Teeth-Brite toothpaste
and become beautiful. Everyone will approve of your choice.
(ii) Polls suggest that President Jones will win the election, so you
may as well vote for him.
(iii) Everyone knows that the Earth is flat, so why do you persist
in your outlandish claims?
(iv) Most educated people know that it is better to use paper bags
than plastic ones. (An appeal to the superior group among whom the position
is supposedly popular. (See also argumentum verecundium).
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)
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:
Ad hominem (abusive): instead of attacking an assertion, the argument
attacks the person who made the assertion.
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.
Ad hominem (tu quoque): this form of attack on the person notes that
a person does not practise what he preaches.
(i) You may argue that God doesn't exist, but you are just a fat idiot.
(ad hominem abusive)
(ii) We should discount what Steve Forbes says about cutting taxes
because he stands to benefit from a lower tax rate. (ad hominem circumstantial)
(iii) We should disregard Fred's argument because he is just angry
about the fact that defendant once cheated him out of $100. (ad hominem
(iv) You say I should give up alcohol, but you haven't been sober for
more than a year yourself. (ad hominem tu quoque)
(v) You claim that Mr. Jones is innocent, but why should anyone listen
to you? You are a Mormon after all. (ad hominem circumstantial)
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
Barker: 166; Cedarblom and Paulsen: 155; Copi and Cohen: 97; Davis:
Appeal to Authority (argumentum ad verecundium)
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
(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, under duress, or otherwise
not being serious
(iv) There is no supporting evidence or argument to justify the position.
If O.J. Simpson (an expert on football) insisted that footballs were made
of cabbage leaves that wouldn't constitute an argument to that effect.
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.
(i) Noted psychologist Elaine Johnson recommends that you buy the EZ-Rest
Hot Tub. (She is not an expert on hot tubs.)
(ii) Economist Alan Greenspan argues that going on the gold standard
will lead to economic prosperity. (Although Greenspan is an expert, not
all economists agree on this point, nor does his saying so make it true.)
(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 The United States
will declare war on Canada. (This is a case of hearsay; in fact, the reporter
said that The United States would not declare war.)
(v) The Los Angeles Times reported that sales were up 8.1 percent this
year. (This is hearsay; we are not in a position to check the Times' sources.)
Point out that either (i) the person cited is not an authority in the
field, or that (ii) being an expert in the field doesn't automatically
make one right and insist that the argument advanced be addressed without
the appeal to authority.
Cedarblom and Paulsen: 155; Copi and Cohen: 95; Davis: 69
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 or how the conclusion was arrived at. Though
this is just a type of appeal to authority, the fallacy is so common it
deserves special mention.
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. Sometimes false and harmful rumours are deliberately
started in order to discredit an opponent.
(i) A government official said today that the new gun law will be proposed
(ii) Experts agree that the best way to prevent nuclear war is to prepare
(iii) It is held that there are more than two million needless operations
conducted every year.
(iv) Rumour has it that the President will declare a national holiday
on his birthday.
Argue that because we don't know the source of the information we have
no way to evaluate the reliability of the information or whether it was
derived rationally. Insist on seeing the proof for yourself.
Style Over Substance
The manner in which an argument (or arguer) is presented is taken to
affect the likelihood that the conclusion is true.
(i) Nixon lost the presidential debate because of the sweat on his
(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?
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
Inductive reasoning consists of inferring from the properties of a sample
to the properties of a whole class of entities.
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 unreliable.
The scope of evidence (in context of course) is too small to support
(i) Fred the Australian, stole my wallet. Thus, all Australians are
thieves. (Of course, we shouldn't judge all Australians on the basis of
(ii) I asked six of my friends what they thought of the new taxes and
they agreed that they are a good idea. The new taxes are therefore generally
(iii) All crows are black. (Even though most of the crows (or even
all of them) we see are black, it would be hasty to make such a generalization
given what we know about the nature of albinos.)
(iv) Pets are nice and cuddly therefore animals are generally nice
Identify the importance of the issue of establishing an appropriate
standard of inductive proof. Then demonstrate what the standard ought to
be in this case and why the author either chose the wrong standard (or
none at all) or didn't meet the correct one.
Barker: 189; Cedarblom and Paulsen: 372; Davis: 103
The examples used in an inductive inference are relevantly different
from the population as a whole.
(i) To see how Americans will vote in the next election we polled a
hundred people in Grenwich Village. This shows conclusively that the Democratic
Party will sweep the polls. (People in Grenwich Village tend to be more
liberal, and hence more likely to vote Democratic, 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 therefore be good. (Of course, the rotten apples may be hidden
beneath the surface where the moisture and darkness facilitate rotting.)
Show how the example cases are relevantly different from the population
as a whole, then show that because the examples are different, the conclusion
does not follow.
Barker: 188; Cedarblom and Paulsen: 226; Davis: 106
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.
(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 a money-making
enterprise, so also must government. (But the objectives of government
and business are completely different, so they will have to meet different
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
The proper conclusion of an inductive argument is denied despite the
evidence to the contrary.
(i) Hugo has had twelve car accidents in 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.)
(iii) Sure that drug has been fatal in 100 previous tests, but how
do you know some unknown factor wasn't present causing the deaths? Maybe
the drug is perfectly safe. (This involves refusing to draw an inductive
conclusion on the basis that some arbitrary assertion has not been disproven.
This is the typical argument of a skeptic. They don't think they need any
evidence to justify their rejection of any generalization no matter how
much evidence points to the other conclusion.
Make the relevant standard of proof clear, point out that the evidence
offered does not meet it, and point out the contrary evidence not taken
into account in the induction. Typically this will lead to either an agreement,
a dispute over the applicability of the specified standard of proof, or
the applicability of the contrary evidence. In each case the argument needs
to be shown to be a rational one rather than some arbitrary choice.
I find that this kind of skepticism of any and all inductive generalization
(except perhaps the ones the author is prejudiced in favor of) is the last
refuge of most sloppy (and dishonest) thinkers since they can assert just
about any possibility (yes, including that an omnipotant god is hiding
the truth from us or that we are just brains in vats manipulated by mad
scientists) to deny the validity of the inductive basis of the positions
of their opponents.
Fallacy of Exclusion ~
Relevant 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".
(i) Ross Perot is over 60 years old. Most people over 60 years old
make make less than $45,000/year therefore Ross Perot probably makes less
than $45,000/year. (This ignores the fact that he owns billions of dollars
worth of stock and other profit-making property.)
(ii) The Jets will probably win this game because they've won nine
out of their last ten. (Eight of their wins came over last place teams,
and today they are playing the first place team.)
Give the missing evidence and show that it is relevant to 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 is relevant to the conclusion.
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 favor welfare cuts." Sometimes the word "generally"
is used, as in "Conservatives generally favor 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.
A general rule is applied when circumstances suggest that an exception
to the rule should apply.
(i) The law says that you should not travel faster than 55 mph, thus
even though your passenger was having a heart attack, you should not have
travelled faster than 55 mph.
(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).
Identify the generalization in question and show that it is relevant
only in a context different from the one in question. Show that the reasons
for the original generalization that justified the rule don't hold in the
Copi and Cohen: 100
Converse Accident ~
An exception to a generalization is applied to cases where the generalization
(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 me to hand mine in late too because I
was lazy and didn't get it done.
Identify the generalization in question and show how the special case
was an exception to the generalization. It helps to make the context under
which the generalization was validated clear since that's typically where
the mistakes are made.
Copi and Cohen: 100