Title: Informal Logic, Famous Fallacies
1Informal Logic, Famous Fallacies
- Dont Be Fooled by Bad Arguments (Part 2)
2Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 15. Begging the Question (Petitio Principii)
- In formal debate, the question is the very
issue being debated, and while debaters can
request a concession of certain points, they
cannot ask a concession of the very point being
debated! - Question Does God Exist?
- Question begging argument
- 1. Prophets inspired by God wrote the bible
- 2. The Bible says God exists
- 3. God exists.
- Parts taken from Hurleys A Concise Introduction
to Logic
3Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- Begging the Question, cont.
- That differs starkly from media uses of the term
Heat Wave Begs the Question Global Warming? - Media should say, Invites the Question Global
Warming?
4Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 16. Complex Question
- Please answer with either Yes or No. Have you
stopped beating your wife? - This question is complex.
- What is implied if you answer yes?
- What is implied if you answer no?
5Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- Complex Question, cont.
- Differs from a leading question, which simply
suggests a given answer - Why do you dislike the defendant? (Complex)
- Do these jeans make my butt look big? (Leading)
6Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 17. Faulty Dilemma (False Dichotomy, False
Bifurcation, Black and White Thinking, Either/Or
fallacy, False Choice) - You must either support the war, or be labeled a
traitor! - There is a tertium quid, a third thing/option
you could seek to end the war for what appear to
be good reasons!
7Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- Faulty Dilemma, cont.
- There are also Trilemmas, Tetralemmas, Etc.
- A famous religious argument
- 1. Jesus must be either Lord, Lunatic, or Liar.
- 2. Cant be Lunatic (teachings are too
impressive) - 3. Cant be liar (hes a paradigm of morality!)
- 4. Jesus must be Lord then, QED!
- Can you think of a forth option that would show
this trilemma faulty?
8Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- Are these genuine dilemmas?
- Either creation or evolution is true.
- You are either with us, or against us (said to
Bobsled teammate who showed up wearing a parka
with a huge hood). - In the age of terrorism, you must choose between
your rights and your safety.
9Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 19 Equivocation
- Generating a faulty conclusion based on using a
single term twice, but with a different meaning
each time - Homosexuality violates the laws of nature
- Violating laws is a crime
- Therefore, homosexual conduct is a crime against
nature - Which term is being used with 2 meanings?
10Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 19 Equivocation
- A mouse is an animal
- Therefore, a large mouse is a large animal.
- Jordy hates things that smell.
- Cooks smell things every day.
- Jordy must hate cooks!
11Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 20. Amphibole
- The police report says he was shot in a secure
area. I hope he can still have children! - Amphiboles occur because of grammatical errors,
missing comas, dangling modifiers, ambiguous
antecedent or pronoun, etc.
12Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- Amphibole, cont.
- John told Henry he made a mistake. It follows
that John at least has the courage to admit his
own mistakes. - Jane said shes giving a lecture about drug use
in her office. Lets go for pizza we all know no
one uses drugs in her office!
13Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 21. Composition
- Mistakenly attributing a feature of the parts to
the whole - 1. Every page of this book is light.
- 2. This book is light.
- No Fallacy
- 1. All these legos are red.
- 2. This dinosaur made with them is red.
14Fallacies of Presumption, Ambiguity, and
Grammatical Analogy
- 22. Division
- Mistakenly attributing a feature of the whole to
its parts - 1. We drafted players from the national
championship team. - 2. We drafted the best players.
- No Fallacy
- 1. This quartet sings on key.
- 2. Joe, the tenor in the quartet, sings on key.
15Quick Quiz
- Every sentence in that paragraph is well-written.
Therefore, that paragraph is well-written.
16Quick Quiz
- Why are you holding a grudge against your high
school classmates?
17Quick Quiz
- George said he was interviewing for a job
drilling oil wells in the supervisors office. We
can conclude that that supervisor has a very
dirty office.
18Quick Quiz
- Emeralds are seldom found in this country, so you
should be careful not to misplace your emerald
ring.
19Quick Quiz
- Tom is super good at getting dogs to follow his
commands! - How do you know that?
- Well, because hes such a good dog trainer!
20Arguments v. Explanations
- In both arguments and explanations, there is at
least one premise, and at least one conclusion.
The crucial difference between them is, the
premises of an argument are better known than the
conclusion, and in an explanation, the conclusion
is better known than the premises. - The terms premise/conclusion arent used for
explanations their parts are called
explanans/explanandum, respectively.
21Arguments v. Explanations
- If an arguments premises guarantee its
conclusion, the argument is deductive. - 1. Edgar ran across the yard.
- 2. Edgar ran.
- Notice the premise is more specific than the
conclusion, illustrating why it is a mistake to
think all deductive arguments move from the
general to the particular. - Consider is the premise better known than the
conclusion?
22Arguments v. Explanations
- If an arguments premises just make the
conclusion likely, the argument is inductive. - 1. The lights are on.
- 2. My parents are home.
- (perhaps the lights are on because a burglar
turned them on, or your parents left them on by
mistake, etc. there is no guarantee your
parents are home from the lights being on.)
23Arguments v. Explanations
- Okay, Dad, I swerved to miss a cat.
- The back end of the car swung around.
- The car is a mess.
- (for the father, the conclusion is well-known,
but the premises are dubious this, then, is
an explanation, not an argument.)