Philosophy 103 Linguistics 103 Even More Introductory Logic: Critical Thinking

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Philosophy 103Linguistics 103Even
MoreIntroductory Logic Critical Thinking

• Dr. Robert Barnard

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Last Time

• Basic Concepts
• Deductive/Inductive
• Valid/Invalid
• Strong/Weak
• Sound
• Cogent
• Started Informal Fallacies

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Plan for Today

• Try to wrap up Informal Fallacies
• Time Permitting Some Philosophical Issues

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Fallacies Review

• Fallacy df A fallacy is a mistake in an
  argument which consists in something other than
  merely false premises
• Fallacies of Relevance
• Appeal to Force (Ad Bacculum)
• Appeal to Pity (Ad Misericodium)
• Appeal to the People (Ad Populum)

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4. Argument against the Person (Ad hominem)

• Attacking the source of an argument instead of
  the argument itself.

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4. Argument against the Person (Ad hominem) (2)

• Ad Hom. Abusive John Kerry says that we should
  spend more state revenue on education because
  doing so would result in a more productive
  workforce. But Kerry is a bleeding-heart, liberal
  Yankee from Massachusetts -- so you know that his
  opinion is worthless.

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4. Argument against the Person (Ad hominem) (3)

• Ad Hom. Circumstantial Barnard says that we
  should spend more state revenue on education. But
  Barnard is a professor who wants a better salary
  -- so you know that his opinion is worthless.

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4. Argument against the Person (Ad hominem)(4)

• Ad Hom From Hypocrisy You've claimed that
  smoking is bad for one's health but you smoke
  too.
• Think about

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4. Argument against the Person (Ad hominem) (5)

• Think about
• Credibility if a person with low credibility
  asserts something without supplying evidence for
  it, then we should withhold judgment.
• Reasons if the person does supply reason for
  the claim, then we still need to look at those
  reasons and evaluate whether they support the
  conclusion in question.
• Contradictory beliefs. If we can show this, then
  we have indeed supplied a good reason to believe
  that the person is confused. People can change
  their minds. Changing your mind is fine
  contradictory beliefs are not.

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5. Accident

• Applying a general rule to a case it was not
  designed to cover.
• Example Killing is bad therefore, it was wrong
  for us to go to war against the Nazi's.

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6. Straw Man

• Attacking an oversimplified version of an
  opponent's actual position.
• Example Those who support gun control are wrong
  they believe that no one should have the right to
  defend themselves in any situation.

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7. Missing the Point/Red Herring

• Two closely related fallacies, which involve
  diverting the listener's attention by changing
  the subject or drawing a slightly different
  conclusion than the one that should be drawn.
• Example The death penalty is the only way to
  punish criminals. Why? Because the justice system
  in this country has gone straight to hell -- what
  with murderers, rapists and robbers getting off
  scot-free! It has got change!

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Another (Common) Red Herring

• Tom Johnson wants the government to pay its
  bills, and not borrow anymore money.
• Joe But Johnson is a tax-and-spend
  big-government politician. Anything he says must
  be wrong!
• Note Red Herring bleeds into Ad Hom.

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Fallacies of Weak Induction

• With these sorts of fallacies, the problem is
  that the premises provide extremely weak support
  for the conclusion. They often disguise this fact
  by involving an emotional appeal of some sort.

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1. Argument from Unqualified Authority

• Arguing for a conclusion based on the testimony
  of someone who is not qualified to speak on the
  relevant subject.
• Example Be careful and look out for lions when
  you go hunting next weekend Coach O says that
  lions migrate south during the winter in the
  United States.

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2. Appeal to Ignorance

• Drawing a conclusion based on a premise which
  states that nothing has been shown.
• Example No one has ever proven that ghosts don't
  exist. Therefore, they obviously do.

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What I saw on Meet the Press

• Russert So can you produce actual
  evidence that there were WMDs in Iraq?
• Talking Head Can you prove there werent?
• Russerts Problem HE DID NOT CALL THE TALKING
  HEAD ON THE FALLACY!!!

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Exception Arguments from Ignorance For Ignorance

• Example You have consistently failed to
  demonstrate your knowledge of the material on the
  exam. Therefore, I don't think you know the
  material.
• (Ignorance IS evidence of ignorance)

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3. Hasty Generalization

• A very bad inductive generalization.
• Example All three of the Ole Miss students I've
  met so far have been from Mississippi so there
  must be no out-of-state students here.

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4. False Cause

• Stating that there is a causal connection when
  one probably does not exist. There are different
  types
• Arguing from Coincidence Example When I've used
  my lucky pen before, I've passed the test
  therefore I'll fail if I don't use that pen.
  (Post Hoc Ergo Propter Hoc)
• Oversimplifying the Cause Example Our society
  is filled with violence and there is a lot of
  violence on TV. It is obvious that the violence
  in society is caused by people watching
  television.
• .

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4. False Cause (2)

• Slippery Slope This is a very common variety of
  the false cause fallacy it involves believing
  without any supporting reasons that X will lead
  to Y.

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Slippery Slope Example

• Legalizing marijuana will lead to the
  legalization of cocaine. If you legalize cocaine,
  you'll be able to buy crack and every other drug
  at your local 7-11.
• (In this argument, it is asserted that the
  legalization of marijuana will lead to (by
  degrees) the legalization of every drug. Once one
  accepts the legalization of marijuana, then one
  is assumed to be on the slippery slope towards
  the legalization of every drug)

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4. False Cause (3)

• Sometimes slippery slope arguments are
  justifiable for instance, if the reasons to
  accept x are just the same reasons that would
  lead you to accept y, then in accepting x, one
  should also accept y.
• BUT, this is because the reasons for X actually
  support Y!

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5. Weak Analogy

• Making a weak analogy, or unfairly comparing one
  thing to something else. It is very difficult to
  evaluate analogies with any degree of precision.
• Example Philosophy 101 is a philosophy class and
  has a lot of discussion Logic is a philosophy
  class. So, it must also have a lot of discussion

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An example of Weak Analogy
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Fallacies of Meaning and Ambiguity

• Fallacies of this variety turn upon mistakes of
  and imprecision in language

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1. Begging the Question

• This can occur in several different forms.
  Essentially, this fallacy occurs when the key
  premise of an argument is unsupported. Here are
  some varieties of this common fallacy
• Circular reasoning Murders have lost the right
  to live because anyone who takes the life of
  another person has given up that right.

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1. Begging the Question (2)

• Concealed Premise Murder is always wrong.
  Therefore, the death penalty is wrong. (The
  concealed premise The death penalty is murder).

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1. Begging the Question (3)

• Wishful Thinking Of course there is life after
  death if I didn't believe that, life would be
  too depressing.

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Dilbert begs the question
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2. Complex Question

• Sometimes called a "loaded question". A question
  which contains a hidden assumption or condition.
• Often, complex questions are such that no matter
  how you answer them, you may be acknowledging
  something you might not want to acknowledge.

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Complex Question Examples

• When did you stop lying to your friends?
• When are you going to give up being a Nazi?
• When did you stop beating your dog?
• How long has it been since your last illicit
  affair?

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3. False Dichotomy or False Dilemma

• Presents as a premise two alternatives as if they
  were the only two available when in fact there
  are more. Often the conclusion is only implied
  and not stated.
• Example Either we elect Mr. X or the economy
  goes down the tubes. The choice should be
  obvious.

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Avoid the False Dichotomy!!

• The way to avoid falling into this trap
• Before you accept X because Y is false, make sure
  there isn't some other alternative that allows
  you to reject X as well.

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4. Suppressed Evidence

• An inductive argument which ignores overriding
  evidence which would prove a different
  conclusion.
• This is common is advertising. Example
  Rent-to-own the cheaper way to buy!
• Quoting out of context can also lead to this
  fallacy, as can ignoring current events.

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5. Equivocation

• Where the conclusion of the argument depends on
  the fact that a word is being used in two
  different senses due to semantic ambiguity (one
  word having two or more definitions).
• Example Every child is a special person. Every
  person should vote against the school bond.
  Therefore, every child should vote against the
  school bond.

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6. Amphiboly

• Where the conclusion of the argument depends on
  the fact that a sentence is syntactically
  ambiguous. (i.e. the sentence allows for more
  than one interpretation of its meaning)
• Ambiguity Example John attacked the man with a
  knife.
• Fallacy Example Norris said he operates a small
  car repair shop. Therefore, you can't take your
  Cadillac to him. (This can be a real problem in
  legal documents).

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7. Composition

• Mistaking properties of the parts for properties
  of the whole.
• Example Every member of the team is a winner
  therefore the team is a winner.
• Not every instance of this type of reasoning is
  bad.
• Additive Quality Example Each one of these
  stamps is valuable. Therefore, the collection of
  stamps as a whole is valuable.

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Even a Viking can do it
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8. Division

• Mistaking properties of the whole for properties
  of the parts.
• Examples
• The Congress is based in Washington D.C.
  therefore each member of Congress is from D.C.
• This football team is the best in the conference
  therefore the quarterback is the best in the
  conference.
• Again, not every instance of this reasoning is
  bad. Pay attention to the context and the details.

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Is the sun coming up, or going down.?
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The Laws of Thought

• Identity
• Non-Contradiction
• Excluded Middle
• Are They all both General and Necessary?

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The Law of Identity

• A true statement is true.
• All A is A.
• Everything is what it is, and not something
  else.
• Everything is self-identical.

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The Law of Non-Contradiction

• Nothing A is not A (a form of identity?)
• No statement is both true and false at the same
  time.
• Nothing is both F and not-F at the same time.
• Opposite qualities are incompatible.
• Everything F is not not-F.

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The Law of Excluded Middle

• Every statement must be either true or false.
• If something is F then it is not not-F.
• Either F or not-F.

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Logic and Psychology

• Where do the laws of thought come from?
• Are they generalizations upon experiences?
• Could we arrive at their general correctness
  without having a variety of experiences?

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Logic and Rhetoric

• Rhetoric is the art of Persuasion
• Logic can be a part of Persuasion
• Informal Fallacies are persuasive cases that
  violate logic.
• Logic Teaches us to know the difference.

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