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Stephen's Guide to the Logical Fallacies
Stephen
Downes*
Overview
Index of Logical Fallacies
Fallacies of
Distraction
Appeals to Motives in Place of Support
Changing the
Subject
Appeal to Authority
Inductive Fallacies
Fallacies Involving Statistical Syllogisms
Causal Fallacies
Missing the Point
Fallacies of
Ambiguity
Category Errors
Non Sequitur
Syllogistic Errors
Fallacies of Explanation
Fallacies of Definition
References
Overview
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.
Reference(s)
Index of Logical Fallacies
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 proposition
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
author
Popularity: a proposition is argued to be true because it is widely held to be
true
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 practice 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 serious
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
dissimilar
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 cause the other
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
effect
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 true
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 causes)
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 should be included)
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)
References
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.
Reference: (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 exist.
(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.
Reference: (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.
Reference: (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 practices? (This asks two questions:
did you use illegal practices, and did you stop?)
Proof: Identify the two propositions illegitimately
conjoined and show that believing one does not mean that you have to believe the
other.
Reference: (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.
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.
Reference: (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.
Reference: (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
false.
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.
Reference: (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 (e.g., "Right
thinking Canadians" or "A reasonable person"). Show that disagreeing with the
conclusion does not make a person "wrong thinking" or "unreasonable".
Reference: (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 whole.
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?
Reference: (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 favorable 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 practice what he preaches.
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 circumstantial)
(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.
Reference: (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 is the
best cure for a recession. (Although Galbraith is an expert, not all economists
agree on this point.)
(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 in 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.
Reference: (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 mention. A variation on this fallacy is the appeal to rumor. Because
the source of a rumor is typically not known, it is not possible to determine
whether to believe the rumor. Very
often false and harmful rumors are deliberately started in 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) Rumor 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 information.
Reference: (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.
Reference: (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 unreliable.
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.
Reference: (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.
Reference: (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.
Reference: (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.
Reference: (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.
Reference: (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 favor welfare cuts." Sometimes the word
"generally" s used, as in "Conservatives generally favor welfare cuts." Or,
sometimes, no specific word is used at all, as in: "Conservatives favor 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.
Accident
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
traveled 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.
Reference: (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.
Reference: (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, “post
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 disappeared.
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.
Reference: (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.
Reference: (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.
Reference: (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.
Reference: (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.
Reference: (Cedarblom and Paulsen: 238)
Missing the Point
These fallacies have in common a general failure to prove
that the conclusion is true.
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.
Reference: (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.
Reference: (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 Canada.
(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 convenience.
Proof: Show that the opposition's argument has been
misrepresented by showing that the opposition has a stronger argument. Describe
the stronger argument.
Reference: (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 meaning.
Equivocation
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.
Reference: (Barker: 163, Cedarblom and Paulsen: 142, Copi
and Cohen: 113, Davis: 58)
Amphiboly
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 pajamas.
(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 interpretations.
Reference: (Copi and Cohen: 114)
Accent
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)
Reference: (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.
Composition
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 whole.
Reference: (Barker: 164, Copi and Cohen: 117)
Division
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.
Reference: (Barker: 164, Copi and Cohen: 119)
Non-Sequitur
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, 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.
Reference: (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.
Reference: (Barker: 69, Cedarblom and Paulsen: 26, Copi and
Cohen: 241)
Inconsistency
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 contraries.
Examples:
(i) Montreal is about 200 km from Ottawa, while Toronto is
400 km from Ottawa. Toronto is closer to Ottawa than Montreal.
(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.
Reference: (Barker: 157)
Syllogistic Fallacies
The fallacies in this section are all cases of invalid
categorical syllogisms.
Fallacy of the Four Terms (quaternio terminorum)
Definition: A standard form categorical syllogism contains
four terms.
Examples:
(i) All dogs are animals, and all cats are mammals, so all dogs are mammals. The
four terms are: dogs, animals, cats and mammals. Note: In many cases, the
fallacy of four terms is a special case of equivocation. While the same word is
used, the word has different meanings, and hence the word is treated as two
different terms. Consider the following example:
(ii) Only man is born free, and no women are men, therefore, no women are born
free. The four terms are: man (in the sense of 'humanity'), man (in the sense of
'male'), women and born free.
Proof: Identify the four terms and where necessary state
the meaning of each term.
References: Copi and Cohen: 206
Undistributed Middle
Definition: The middle term in the premises of a standard
form categorical syllogism never refers to all of the members of the category it
describes.
Examples:
(i) All Russians were revolutionists, and all anarchists were revolutionist,
therefore, all anarchists were Russians.
The middle term is 'revolutionist'. While both Russians and anarchists share the
common property of being revolutionist, they may be separate groups of
revolutionists, and so we cannot conclude that anarchists are otherwise the same
as Russians in any way. Example from Copi and Cohen, 208.
(ii) All trespassers are shot, and someone was shot, therefore, someone was a
trespasser. The middle term is 'shot'. While 'someone' and 'trespassers' may
share the property of being shot, it doesn't follow that the someone in question
was a trespasser; he may have been the victim of a mugging.
Proof: Show how each of the two categories identified in
the conclusion could be separate groups even though they share a common
property.
References: Copi and Cohen: 207
Illicit Major
Definition: The predicate term of the conclusion refers to
all members of that category, but the same term in the premises refers only to
some members of that category.
Examples:
(i) All Texans are Americans, and no Californians are Texans, therefore, no
Californians are Americans. The predicate term in the conclusion is 'Americans'.
The conclusion refers to all Americans (every American is not a Californian,
according to the conclusion). But the premises refer only to some Americans
(those that are Texans).
Proof: Show that there may be other members of the
predicate category not mentioned in the premises which are contrary to the
conclusion. For example, from (i) above, one might argue, "While it's true that
all Texans are Americans, it is also true that Ronald Regan is American, but
Ronald Regan is Californian, so it is not true that No Californians are
Americans."
References: Copi and Cohen: 207
Illicit Minor
Definition: The subject term of the conclusion refers to
all members of that category, but the same term in the premises refers only to
some members of that category.
Examples:
(i) All communists are subversives, and all communists are critics of
capitalism, therefore, all critics of capitalism are subversives. The subject
term in the conclusion is 'critics of capitalism'. The conclusion refers to all
such critics. The premise that 'all communists are critics of capitalism' refers
only to some critics of capitalism; there may be other critics who are not
communists.
Proof: Show that there may be other members of the subject
category not mentioned in the premises which are contrary to the conclusion. For
example, from (i) above, one might argue, "While it's true that all communists
are critics of capitalism, it is also true that Thomas Jefferson was a critic of
capitalism, but Thomas Jefferson was not a subversive, so not all critics of
capitalism are subversives."
References: Copi and Cohen: 208
Exclusive Premises
Definition: A standard form categorical syllogism has two
negative premises (a negative premise is any premise of the form 'No S are P' or
'Some S is not P').
Examples:
(i) No Manitobans are Americans, and no Americans are Canadians, therefore, no
Manitobans are Canadians. In fact, since Manitoba is a province of Canada, all
Manitobans are Canadians.
Proof: Assume that the premises are true. Find an example
which allows the premises to be true but which clearly contradicts the
conclusion.
References: Copi and Cohen: 209
Fallacy of Drawing an Affirmative Conclusion From a Negative Premise
Definition: The conclusion of a standard form categorical
syllogism is affirmative, but at least one of the premises is negative.
Examples:
(i) All mice are animals, and some animals are not dangerous, therefore some
mice are dangerous.
(ii) No honest people steal, and all honest people pay taxes, so some people who
steal pay taxes.
Proof: Assume that the premises are true. Find an example
which allows the premises to be true but which clearly contradicts the
conclusion.
References: Copi and Cohen: 210
Existential Fallacy
Definition: A standard form categorical syllogism with two
universal premises has a particular conclusion. The idea is that some universal
properties need not be instantiated. It may be true that 'all trespassers will
be shot' even if there are no trespassers. It may be true that 'all brakeless
strains are dangerous' even though there are no brakeless strains. That is the
point of this fallacy.
Examples:
(i) All mice are animals, and all animals are dangerous, so some mice are
dangerous.
(ii) No honest people steal, and all honest people pay taxes, so some honest
people pay taxes.
Proof: Assume that the premises are true, but that there
are no instances of the category described. For example, in (i) above, assume
there are no mice, and in (ii) above, assume there are no honest people. This
shows that the conclusion is false.
References: Copi and Cohen: 210
Fallacies of
Explanation
An explanation is a form of reasoning which attempts to
answer the question "why?" For example, it is with an explanation that we answer
questions such as, "Why is the sky blue?" A good explanation will be based on a
scientific or empirical theory. The explanation of why the sky is blue will be
given in terms of the composition of the sky and theories of reflection.
Subverted Support
Definition: An explanation is intended to explain who some phenomenon happens.
The explanation is fallacious if the phenomenon does not actually happen of if
there is no evidence that it does happen.
Examples:
(i) The reason why most bachelors are timid is that their mothers were
domineering.
(This attempts to explain why most bachelors are timid. However, it is not the
case that most bachelors are timid.)
(ii) John went to the store because he wanted to see Maria.
(This is a fallacy if, in fact, John went to the library.)
(iii) The reason why most people oppose the strike is that they are afraid of
losing their jobs.
(This attempts to explain why workers oppose the strike. But suppose they just
voted to continue the strike, then in fact, they don't oppose the strike. [This
sounds made up, but it actually happened.])
Proof : Identify the phenomenon which is being explained.
Show that there is no reason to believe that the phenomenon has actually
occurred.
References: Cedarblom and Paulsen: 158
Non-Support
Definition: An explanation is intended to explain who some
phenomenon happens. In this case, there is evidence that the phenomenon
occurred, but it is trumped up, biased or ad hoc evidence.
Examples:
(i) The reason why most bachelors are timid is that their mothers were
domineering.
(This attempts to explain why most bachelors are timid. However, it is shown
that the author bases his generalization on two bachelors he once knew, both of
whom were timid.)
(ii) The reason why I get four or better on my evaluations is that my students
love me.
(This is a fallacy when evaluations which score four or less are discarded on
the grounds that the students did not understand the question.)
(iii) The reason why Alberta has the lowest tuition in Canada is that tuition
hikes have lagged behind other provinces.
(Lower tuitions in three other provinces - Quebec, Newfoundland and Nova Scotia
- were dismissed as "special cases" [again this is an actual example].)
Proof: Identify the phenomenon which is being explained.
Show that the evidence advanced to support the existence of the phenomenon was
manipulated in some way.
References: Cedarblom and Paulsen: 160
Untestability
Definition: The theory advanced to explain why some phenomenon occurs cannot be
tested. We test a theory by means of its predictions. For example, a theory may
predict that light bends under certain conditions, or that a liquid will change
color if sprayed with acid, or that a psychotic person will respond badly to
particular stimuli. If the predicted event fails to occur, then this is evidence
against the theory.
A theory cannot be tested when it makes no predictions. It
is also untestable when it predicts events which would occur whether or not the
theory were true.
Examples:
(i) Aircraft in the mid-Atlantic disappear because of the effect of the Bermuda
Triangle, a force so subtle it cannot be measured on any instrument.
(The force of the Bermuda Triangle has no effect other than the occasional
downing of aircraft. The only possible prediction is that more aircraft will be
lost. But this is likely to happen whether or not the theory is true.)
(ii) I won the lottery because my psychic aura made me win.
(The way to test this theory to try it again. But the person responds that her
aura worked for that one case only. There is thus no way to determine whether
the win was the result of an aura or luck.)
(iii) The reason why everything exists is that God created it.
(This may be true, but as an explanation it carries no weight at all, because
there is no way to test the theory. No evidence in the world could possibly show
that this theory is false, because any evidence would have to be created by God,
according to the theory.)
(iv) NyQuil makes you go to sleep because it has a dormative formula.
(When pressed, the manufacturers define a "dormative formula" as "something
which makes you sleep". To test this theory, we would find something else which
contains the domative formula and see if makes you go to sleep. But how do we
find something else which contains the dormative formula? We look for things
which make you go to sleep. But we could predict that things which make you
sleep will make you sleep, no matter what the theory says. The theory is empty.)
Proof: Identify the theory. Show that it makes no
predictions, or that the predictions it does make cannot ever be wrong, even if
the theory is false.
References: Cedarblom and Paulsen: 161
Limited Scope
Definition: The theory doesn't explain anything other than the phenomenon it
explains.
Examples:
(i) There was hostility toward hippies in the 1960s because of their parents'
resentment toward children.
(This theory is flawed because it explains hostility toward hippies, and nothing
else. A better theory would be to say there was hostility toward hippies because
hippies are different, and people fear things which are different. This theory
would explain not only hostility toward hippies, but also other forms of
hostility.)
(ii) People get schizophrenia because different parts of their brains split
apart.
(Again, this theory explains schizophrenia - and nothing else.)
Proof: Identify the theory and the phenomenon it explains.
Show that the theory does not explain anything else. Argue that theories which
explain only one phenomenon are likely to be incomplete, at best.
References: Cedarblom and Paulsen: 163
Limited Depth
Definition: Theories explain phenomena by appealing to some underlying cause or
phenomena. Theories which do not appeal to an underlying cause, and instead
simply appeal to membership in a category, commit the fallacy of limited depth.
Examples:
(i) My cat likes tuna because she's a cat.
(This theory asserts only that cats like tuna, without explaining why cats like
tuna. It thus does not explain why my cat likes tuna.)
(ii) Ronald Reagan was militaristic because he was American.
(True, he was American, but what was it about being American that made him
militaristic? What caused him to act in this way? The theory does not tell us,
and hence, does not offer a good explanation.)
(iii) You're just saying that because you belong to the union.
(This attempt at dismissal tries to explain your behavior as frivolous.
However, it fails because it is not an explanation at all. Suppose everyone in
the union were to say that. Then what? We have to get deeper - we have to ask
why they would say that - before we can decide that what they are saying is
frivolous.)
Proof: Theories of this sort attempt to explain a
phenomenon by showing that it is part of a category of similar phenomenon.
Accept this, then press for an explanation of the wider category of phenomenon.
Argue that a theory refers to a cause, not a classification.
References: Cedarblom and Paulsen: 164
Fallacies of Definition
In order to make our words or concepts clear, we use a
definition. The purpose of a definition is to state exactly what a word means. A
good definition should enable a reader to 'pick out' instances of the word or
concept with no outside help.
For example, suppose we wanted to define the word "apple".
If the definition is successful, then the reader should be able go out into the
world and select every apple which exists, and only apples. If the reader misses
some apples, or includes some other items (such as pears), or can't tell whether
something is an apple or not, then the definition fails.
Too Broad
Definition: The definition includes items which should not be included.
Examples:
(i) An apple is something which is red and round.
(The planet Mars is red and round. So it is included in the definition. But
obviously it is not an apple.)
(ii) A figure is square if and only if it has four sides of equal length.
(Not only squares have four sides of equal length; trapezoids do as well.
Proof: Identify the term being defined. Identify the
conditions in the definition. Find an item which meets the condition but is
obviously not an instance of the term.
References: Cedarblom and Paulsen: 182
Too Narrow
Definition: The definition does not include items which should be included.
Examples:
(i) An apple is something which is red and round.
(Golden Delicious apples are apples, however, they are not red (they are
yellow). Thus they are not included in the definition, however, they should be.)
(ii) A book is pornographic if and only if it contains pictures of naked people.
(The books written by the Marquis de Sade do not contain pictures. However, they
are widely regarded as pornographic. Thus, the definition is too narrow.
(iii) Something is music if and only if it is played on a piano.
(A drum solo cannot be played on a piano, yet it is still considered music.)
Proof: Identify the term being defined. Identify the
conditions in the definition. Find an item which is an instance of the term but
does not meet the conditions.
References: Cedarblom and Paulsen: 182
Failure to Elucidate
Definition: The definition is harder to understand than the
term being defined.
Examples:
(i) Someone is lascivious if and only if he is wanton.
(The term being defined is "lascivious". But the meaning of the term "wanton" is
just as obscure as the term "lascivious". So this definition fails to
elucidate.)
(ii) An object is beautiful if and only if it is aesthetically successful.
(The term "aesthetically successful" is harder to understand than the term
"beautiful".
Proof: Identify the term being defined. Identify the
conditions in the definition. Show that the conditions are no more clearly
defined than the term being defined.
References: Cedarblom and Paulsen: 184
Circular Definition
Definition: The definition includes the term being defined
as a part of the definition. (A circular definition is a special case of a
Failure to Elucidate.)
Examples:
(i) An animal is human if and only if it has human parents.
(The term being defined is "human". But in order to find a human, we would need
to find human parents. To find human parents we would already need to know what
a human is.
(ii) A book is pornographic if and only if it contains pornography.
(We would need to know what pornography is in order to tell whether a book is
pornographic.)
Proof: Identify the term being defined. Identify the
conditions in the definition. Show that at least one term used in the conditions
is the same as the term being defined.
References: Cedarblom and Paulsen: 184
References
The following list surveys major texts in logic and
critical reasoning. Although not a complete guide (could there be such a thing?)
it should provide a good starting point. Although historical material is
present, I have restricted selections to books published in this century.
* Barker, Stephen F. The Elements of Logic. Fifth Edition.
McGraw-Hill, 1989.
Barker is one of the heavyweight thinkers in formal logic
and his book reads like it. For the rest of us, that means: dense and
unenlightening. The book covers categorical syllogisms, truth functions,
quantification, fallacies, and inductive reasoning.
* Boolos, George., and Jeffrey, Richard. Computability and
Logic. Second Edition. Cambridge University Press, 1980.
A fascinating look at the overlap between computation and
logic. Heavy going; it begins with Turing Machines, ponders undecidability,
indefinability and incompleteness, and ends with Ramsey's theorems. People who
like heavy symbolism will love this book. People who think it's all squiggles
will hate it. Recommended.
* Bergmann, Merrie, James Moor, and Jack Nelson. The Logic
Book. Second Edition. McGraw-Hill, 1990.
This is the introduction to formal logic. Covers syntax and
semantics in propositional and predicate calculus. Introduces the concepts of
completeness and decidability. The second edition was the first new edition in
ten years, which speaks well for its stability. Recommended.
* Cohen, Morris, and Nagel, Ernest. An Introduction to
Logic. Harcourt, Brace and World, 1932, 1962.
A traditional text, this book examines categorical
syllogisms and touches on mathematical systems and probability. In other words,
it's a (very) uneasy blend of classical logic and modern. Worth a look for its
historical value.
* Copi, Irving M. and Cohen, Carl. Introduction to Logic.
Eighth Edition. Macmillan, 1990.
For many years, Copi was the standard introductory text,
and this edition continues the trend. Covers propositional logic, categorical
syllogisms, and informal fallacies. A new edition appears every few years, which
is hell on used book stores. Copi is the master of the circle-and-arrow argument
diagrams (which never really worked, in my view). Better introductory texts have
appeared in recent years.
* Gianelli, A.P. Meaningful Logic. Bruce Publishing
Company, 1962.
This is a classical logic text with numbered paragraphs and
a focus on the universal and the particular. All this sounds bad but the author
is an engaging and earnest writer. This book is useless to somebody who wants to
learn logic, but a treasure to someone who knows and loves the discipline.
* Gilbart, Helen W. Reading With Confidence. Scott, Foresman and Company, 1988.
This is the sort of stuff that is passing for 'critical
thinking' in education these days. This very basic text begins by looking at
'controlling ideas', transitions, context, inference, bias and prejudice. It's a
noble objective, but it's fuzzy and in some places just wrong. Not recommended.
* Haack, Susan. Philosophy of Logics. Cambridge University
Press, 1978.
This book is serious reading and should not be attempted
without a good grounding in the field. Covers theories of truth, paradoxes,
classical and non-classical logics, problems in modal logic (including relevance
logic), and many-valued logic. Fascinating.
* Huff, Darrell. How to Lie With Statistics. W.W. Norton,
1954.
I have the 38th printing, which should be an indication of
this slim book's popularity. A classic in the field and a must read for anybody
who reads newspapers or magazines. Although the examples are seriously dated,
the material is not. For some reason, many of the tricks Huff discusses are not
covered in more standard texts. Recommended.
* Hughes, G.H., and Cresswell, M.J. An Introduction to
Modal Logic. Methuen and Co. Ltd., 1968.
For many years the standard introduction to modal logic,
this book is a must read for anyone seriously interested in advanced topics.
Covers both propositional and predicate modal logic. It was my Bible in 1987.
Recommended.
* Jason, Gary. Introduction to Logic. Jones and
Bartlett,1994.
A standard introductory text, this book covers informal
fallacies and propositional logic. Instead of describing categorical logic, it
instead treats the subject (more accurately, in my view) as a branch of set
theory and the logic of properties and relations. Mill's Methods are relegated
to an appendix; now that hurts! Jason uses squares and circles instead of the
usual letters to stand for propositions in inference rules; this is a tactic
which worked well in my own classes.
* Jager, Ronald. Essays in Logic From Aristotle to Russell.
Prentice-Hall, 1963.
Contains selections from Aristotle, John Stuart Mill, Lewis
Carroll(!), John Dewey, Bertrand Russell, Henry Veatch and Gilbert Ryle. This
makes it eclectic, to say the least, but interesting reading.
* Jeffrey, Richard. Formal Logic: Its Scope and Limits.
McGraw-Hill, 1981, 1967.
A beautiful book and an absolute must for any serious
student of logic or computation. Can be used as an introductory text, but this
use is not recommended. While it focuses entirely on deductive logic, its crisp
definitions and theorems supplement a traditional (truth table) method of
derivation along with truth trees. Jeffry is particularly strong on completeness
and decidability. Recommended.
* Johnson, R.H., and Blair, J.A. Logical Self-Defense.
McGraw-Hill Ryerson, 1983, 1977.
This book focuses almost entirely on informal fallacies and
is intended for an audience that wants to read newspapers more critically. A
noble objective but its limited scope means that a study of logic is better
served by other texts.
* Kahane, Howard. Logic and Philosophy: A Modern
Introduction. Wadsworth, 1990.
A standard introductory text covering propositional and
syllogistic logic, induction and fallacies. Part five is good: discussions of
modal, deontic and epistemic logic along with an introduction to axiom systems.
* Kelly, David. The Art of Reasoning. W.W. Norton, 1988.
A very nice blend of formal and informal argument forms.
Covers definition, propositional and predicate logic, and inductive reasoning.
Incorporates a number of effective graphical aids, especially in the discussion
of definition (which precedes the discussion of propositions, a welcome change
from what has become standard form of late). Recommended as a good first logic
text.
* Mayfield, Marlys. Thinking for Yourself: Developing
Critical Thinking Skills Through Writing. Wadsworth Publishing Company, 1987.
A very informal text which relies more on contemporary
teaching strategies (such as 'discovery exercises' and memory maps). A strongly
American political view of the world permeates this work. Not recommended.
* Pospesel, Howard. Introduction to Logic: Propositional
Logic. Second Edition. Prentice-Hall, 1984.
An outstanding teaching book illustrated with contemporary
(for 1984) cartoons and lively examples. Uses arrow to represent the conditional
operator instead of the standard horseshoe. Recommended.
* Purtill, Richard L. Logic for Philosophers. Harper and
Row, 1971.
The book is dedicated to Rudolf Carnap, an insignia which
should alert the reader to expect staunch formalism throughout. Purtill doesn't
disappoint. The book covers propositional, syllogistic, class, and modal logic.
* Putnam, Hilary. Philosophy of Logic. Harper, 1971.
Heady, engaging, and Putnam at his expository best, this
book is required reading for those interested in some of the issues beneath the
surface of logic, and especially the realism-nominalism debate. Not for
beginners.
* Quine, Willard Van Orman. Methods of Logic. Fourth
Edition. Harvard University Press, 1950, 1959.
An authoritative text. Quine focuses entirely on deductive
forms: truth functional logic and quantification. Quine's unorthodox symbolism
makes this book inappropriate for the novice. Essential for students for Quine's
philosophy.
* Rescher, Nicholas. Introduction to Logic. St. Martin’s
Press, 1964.
Rescher's book forms the foundation for Copi's Introduction
to Logic and hence covers syllogistic forms, informal fallacies, propositional
logic and inductive logic. A useful text for the novice, but Copi is more up to
date. Rescher himself is one of my favorite authors.
* Salmon, Merrilee. Introduction to Logic and Critical
Thinking. Harcourt Brace Jovanovich, 1984.
Quickly covers deductive forms, but the bulk of the book is
devoted to inductive argument, conditionals, confirmation of hypotheses, and
arguments based on relations. Thus it has a lot of material not covered by other
texts, but is not for the beginner.
* Salmon, Wesley. Logic. Third Edition. Prentice-Hall,
1983.
Part of the widely popular (and vastly overpriced)
Foundations of Philosophy Series, this slim volume covers basic deduction,
induction, and some issues in logic and language. This is not a teaching text,
as there are no exercises. Actually, it's hard to say why it was written, except
perhaps to round out the series. Wesley Salmon is authoritative; this book is
not.
* Schagrin, Morton L. The Language of Logic: A Programmed
Text. Random House, 1968.
This is a good idea which didn't really work. The reader
works through a series of 'frames' and goes to different frames depending on how
they answer questions. A lot like hypertext, only slower. The book should never
have been printed in Helvetica.
* Sellars, Roy Wood. The Essentials of Logic. Revised
Edition. The Riverside Press, 1925.
This transitional text resembles eighteenth century works
but attempts to come to grips with the formal and mathematical nature of logic
newly discovered in the late nineteenth and early twentieth centuries. For
students of the history of logic only.
* Skyrms, Brian. Choice and Chance: An Introduction to
Inductive Logic. Dickenson, 1966.
A nice compact treatment of the major problems in inductive
logic. Includes a lengthy (though dated) treatment of the traditional problem of
induction along with and Goodman's new problem.
* Stephens, William N. Hypotheses and Evidence. Thomas Y.
Crowell, 1968.
As the title indicates, this text focuses on induction,
causality, hypotheses, theories and evidence. Unfortunately, it came out before
a lot of the recent and important work in the area and so is of historical
interest only.
* Thomason, Richmond. Symbolic Logic: An Introduction.
Collier-Macmillan, 1970.
Required reading for any student of philosophy, mathematics
or the harder sciences. Reads more easily than The Logic Book and provides a
thorough introduction to the semantics, in addition to the syntax, of standard
argument forms. Additionally, Thomason covers identity, set theory and
mathematical induction. Not for the beginner.
* Weston, Anthony. A Rulebook for Arguments. Hackett, 1987.
This slim volume (93 pages) serves as an excellent
introduction for novices. The text surveys commonly used argument forms:
arguments by example, arguments by analogy, etc. and shows the reader how to use
proper argument form in essays. Recommended.
* Yanal, Robert J. Basic Logic. West Publishing Company,
1988.
Exactly as the title suggests. Uses a version of Copi's
circle-and-arrow diagrams (but instead of using numbers, he uses phrases - a big
improvement). Covers arguments, deductive logic and inductive logic. Ho hum.
______
* Courtesy of “Stephen Downe's Guide to the
Logical Fallacies”
Stephen Downes, May 1995.
Dr. Downes is Information Architect, University of Alberta, Edmonton, Alberta,
Canada.
Email: <stephen.downes@ualberta.ca>
See original at < http://www.datanation.com/fallacies/index.htm >.
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