Logical Fallacies

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Logical Fallacies

• Continuing our foray into the world of argument

Monty Python
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What is Fallacy?

• The art of the argument is thousands of years
  old, so too is the study of the faults of
  arguments called fallacies. They are flaws and
  faults that weaken arguments.
• They try to persuade without providing
  legitimate grounds for accepting the conclusions.
  
• Fallacious...
• People may commit them accidentally or use them
  deliberately to manipulate others.

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• Logical fallacies can be formal or informal.
• They are both arguments that sound persuasive
• but, fail to provide logical support for their
  conclusions.
• Formal ...
• Informal ...

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Formal Fallacy

• A formal fallacy is one which involves an error
  in the form, arrangement or technical structure
  of an argument.
• The question in view is not whether a
  conclusion is true or false, but whether the form
  of the argument is correct or incorrect valid
  or invalid.
• The concluding statement of an argument may be
  objectively true, though the argument is formally
  invalid or the concluding statement may be
  objectively false, though the argument is
  formally valid. Here are some examples

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• Formally Valid Arguments
• 1. True and Valid All men are mortal.Socrates
  is a man.Therefore Socrates is mortal.
• 2. False but Valid All men are green.Socrates
  is a man.Therefore Socrates is green.
• In this example, the first statement is false,
  but the form or structure of the argument is
  correct or valid. (If all men were green then
  Socrates would be also).

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• Formally Invalid Arguments
• 3. False and Invalid Some men are
  green.Socrates is a man.Therefore Socrates is
  green.
• 4. True but Invalid Some men are
  mortal.Socrates is a man.Therefore Socrates is
  mortal.
• In these examples, the first statement says
  something about some men, not about all men. One
  could correctly reason from this first statement
  that Socrates might possibly be green or mortal,
  but he could not correctly reason that Socrates
  necessarily is green or mortal.

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Informal Fallacy

• As with most things philosophical, there is no
  common agreement on all aspects of argument
  faults, but types of mistakes made in informal
  arguments are usually grouped into these three
  broad areas
• .
• .
• .

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• 1) FALLACIES OF RELEVENCE
• These are fallacies that introduce
• evidence to support an argument
• that really have no relationship to the
  argument hence the evidence is irrelevant to the
  conclusion.
• Here are some common fallacies of relevance

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Attack on the Person

• This fallacy tries to counter an argument made
  by someone else by attacking that person, not the
  argument. Example
• So you think the Earth is round. What do you
  know? You're just a kid!
• No effort is made to address the argument made
  by 'the kid'. It instead attacks the kid. This
  type of argument can also be called poisoning the
  well, when you try to discredit someone before
  they have a chance to make their argument, and is
  often used in court to damage the reputation of a
  witness.

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Appeal to Ignorance

• Definition In the appeal to ignorance, the
  arguer basically says, "Look, there's no
  conclusive evidence on the issue at hand.
  Therefore, you should accept my conclusion on
  this issue."
• Example "People have been trying for centuries
  to prove that God exists. But no one has yet been
  able to prove it. Therefore, God does not exist."
  
• Here's an opposing argument that commits the
  same fallacy
• "People have been trying for years to prove that
  God does not exist. But no one has yet been able
  to prove it. Therefore, God exists."

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Attack to Popularity

• If most people believe something does that make
  it true? Not necessarily. Examples of this type
  of fallacy include
• "More people went to see this movie than any
  other, so it must be the best!
• Everyone knows that the world is flat, so it
  must be flat"
• Just because a lot of fools do something or
  believe in something doesn't make it so. It
  certainly doesn't make for a good argument. The
  classic refutation (comeback) for this one is
• If everyone went and jumped off the bridge,
  would you?"

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Attack to Authority

• There are a variety of fallacies related to this
  one, which is based on the idea that an expert
  (an authority) knows something.
• This is a tricky one, because sometimes evidence
  presented by an expert is more reliable than
  evidence presented by anyone else-for example,
  someone trained in auto repair probably knows
  more about auto repair than someone not so
  trained. On the other hand, some experts are not
  so expert
• Paris Hilton says that there is life on Mars, so
  there must be life on Mars, because she's famous
  and famous people know lots of things non-famous
  people don't.

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Appeal to Emotion

• This is a group of fallacies related to an
  argument that appeals to the emotions, rather
  than to reason. Examples include
• Scare tactic (fear)If you vote for him, he'll
  start a war!
• PityI realize I'm not qualified, but if you
  don't give me this job, my children will starve!
• RidiculeThat's a really dumb idea! Sure, like
  the world is round! What a buffoon!
• SpiteI know you all hate her for being mean to
  you, so she doesn't deserve the award for best
  singer .

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Red Herring

• Definition Partway through an argument, the
  arguer goes off on a tangent, raising a side
  issue that distracts the audience from what's
  really at stake. Often, the arguer never returns
  to the original issue.
• Example "Grading this exam on a curve would be
  the most fair thing to do. After all, classes go
  more smoothly when the students and the professor
  are getting along well." Let's try our
  premise-conclusion outlining to see what's wrong
  with this argument
• Premise Classes go more smoothly when the
  students and the professor are getting along
  well.
• Conclusion Grading this exam on a curve would be
  the most fair thing to do.

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• When we lay it out this way, it's pretty obvious
  that the arguer went off on a tangent--the fact
  that something helps people get along doesn't
  necessarily make it more fair fairness and
  justice sometimes require us to do things that
  cause conflict.
• But the audience may feel like the issue of
  teachers and students agreeing is important and
  be distracted from the fact that the arguer has
  not given any evidence as to why a curve would be
  fair.

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2) Fallacies of Ambiguity

• These fallacies are often not deliberate, though
  they can be. They are misuses of language.
• Two of the most common are
• .

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Amphiboly

• These are errors related to grammatical
• misconstruction, which leads to a
• confusing conclusion, such as this traffic sign
• Slow children playing. This could mean
• a. Proceed slowly, as there are children playing
  here.
• b. The children playing here are slow. In many
  cases, people familiar with the situation would
  be able to interpret the intended meaning.
• Amphiboly can have serious consequences in legal
  documents, for example, in arguments over the
  interpretation of a phrase.

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Equivocation

• This fallacy is perhaps the most simple and
  obvious of the fallacies of ambiguity. Here, a
  single term is used with two or more meanings in
  the same argument.
• The term equivocation comes from the Latin - and
  means "with equal voice". When a term is used
  univocally in an argument, it always has the same
  meaning, but when it is used equivocally, more
  than one meaning is given equal voice.
• Here is an amusing example of an argument using
  this fallacy

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• It is well known that the average
• family has 2.5 children (premise 1).
• Well, Jane's family is very average
• (premise 2), so they must have
• 2.5 children (conclusion).
• The problem here is that the key term average is
  used in more than one sense. With the premise,
  the term is used in the sense of statistical
  averages. But the second premise switches to
  another sense of average, this time meaning not
  unusual.
• By equating the two, the absurd conclusion of a
  family having fractional children is reached

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3) Fallacies of Presumption

• ...
• They differ from fallacies of relevance in that
  the information may be relevant to the argument.
• But it may be based upon an assumption that
  cannot be substantiated. These fallacies are more
  likely to involve errors of form than relevance
  or ambiguity fallacies.
• Here are some common examples

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Hasty Generalization

• Definition Making assumptions about a whole
  group or range of cases based on a sample that is
  inadequate (usually because it is atypical or
  just too small).
• Stereotypes about people ("frat boys are
  drunkards," "grad students are nerdy," etc.) are
  a common example of the principle underlying
  hasty generalization.
• Example "My roommate said her philosophy class
  was hard, and the one I'm in is hard, too. All
  philosophy classes must be hard!" Two people's
  experiences are, in this case, not enough on
  which to base a conclusion.
• The scope of evidence (in context of course) is
  too small to support the conclusion.

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Slippery Slope

• Definition The arguer claims that a sort of
  chain reaction, usually ending in some dire
  consequence, will take place, but there's really
  not enough evidence for that assumption.
• The arguer asserts that if we take even one step
  onto the "slippery slope," we will end up sliding
  all the way to the bottom he or she assumes we
  can't stop halfway down the hill.

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• Example "Animal experimentation reduces our
  respect for life. If we don't respect life, we
  are likely to be more and more tolerant of
  violent acts like war and murder. Soon our
  society will become a battlefield in which
  everyone constantly fears for their lives.
• It will be the end of civilization. To prevent
  this terrible consequence, we should make animal
  experimentation illegal right now."
• Since animal experimentation has been legal for
  some time and civilization has not yet ended, it
  seems particularly clear that this chain of
  events won't necessarily take place.

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False Cause

• These fallacies make connections between bits of
  evidence where connections are not really
  present. Using with this, therefore because of
  this ergo mixes up only coincidentally related
  evidence and draws a relationship between them.
• A causes B (without real proof that this causal
  relationship actually exists).
• This causal relationship is often claimed when
  there is correlation between A and B (that they
  vary together) or a relatively distant causal
  connection.
• Example
• It is dark now, which makes it very dangerous.
  It is not the dark that causes danger.
• This can occur in medicine, where a set of
  symptoms can lead to an incorrect diagnosis of a
  disease or illness that is actually caused by
  something else.

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Two Wrongs

• This fallacy "Occurs when a debater makes an
  argument urging the audience to accept, or
  condone, one thing that is wrong because another
  similar thing, also wrong, has been accepted and
  condoned
• For example
• Speaker A You shouldn't embezzle from your
  employer. It's against the law.
• Speaker B My employer cheats on their taxes.
  That's against the law, too.
• The unstated premise is that breaking the law
  (the wrong) is justified, as long as the other
  party also does so. It is often used as a red
  herring, or an attempt to change or distract from
  the issue.

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Complex Question

• Also called a loaded question, this fallacy
  involves posing a question in such a way that by
  either affirming or denying it implies agreeing
  to something controversial in the question. The
  classic example is
• Have you stopped beating your wife?
• If you answer no, it implies that you are
  continuing this abhorrent practice and are not a
  nice person. If you answer yes, it means that,
  while you have now ceased this practice, you are
  admitting that you did it in the past. The
  question is complex, because it is actually
  lumping two questions into one.

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False Dilemma

• This fallacy involves artificially narrowing the
  choices available and then demanding that someone
  pick from this limited selection of choices. This
  fallacy is also known as black-or-white of a
  false dichotomy (a dichotomy being a two-ness).
  The syllogistic form of the disjunction is often
  used to create the dilemma
• A or BNot ATherefore B.
• The trick in rhetoric is to present only this
  clear choice and then to make the choice of A
  repugnant. An example from Canadian history was
  the 1935 Liberal election slogan "It's King or
  it's chaos!" which implied that if voters choose
  other than King, they would be voting for chaos.
  Of course this was not, strictly speaking, true.

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• Article discussing election fallacies

Top 10 Logical Fallacies in Politics -
Monty Burns Campaign - Simpsons