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Logical Fallacies

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TAMIU Writing Center

on 25 August 2014

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Transcript of Logical Fallacies

What are Logical Fallacies?
Fallacy Taxonomy
Formal Fallacy
- error in form/structure
Appeal to Probability
Affirming the Consequent
Formal Fallacies
Appeal to Probability
- assuming something to be true because it is probably true (or might possibly be true)





"The Weather Channel host said to expect rain tomorrow.
Therefore, it will rain tomorrow."

"Public restrooms are often filthy.
Therefore, the restrooms at TAMIU are filthy."
Affirming the Consequent
1. If P, then Q.
2. Q.
3. Therefore, P.




"If I have a cold, I have a fever.
I have a fever.
Therefore, I have a cold."

"If it rained outside, the grass will be wet.
The grass is wet.
Therefore, it rained outside."
Logical Fallacies
This presentation outlines commonly-used logical fallacies often found in students' work. You can use the arrows below or on your keyboard to navigate.
Updated 7-14-2014
A fallacy is faulty reasoning which renders an argument invalid. Fallacies can be formal or informal.
We will cover only the
most common
fallacies.

Complete list of fallacies:
http://en.wikipedia.org/wiki/List_of_fallacies
Informal Fallacy
- error in content/premises
Begging the Question
Fallacy of Composition
False Dilemma
Red Herring Fallacies
Ad Hominem
Argumentum ad Populum
Appeal to Authority
Straw Man
Faulty Generalizations
Cherry Picking
Hasty Generalization
False Analogy
Red Herring Fallacies
Red Herring Fallacies
- any argument which derails the actual conversation at hand or is otherwise irrelevant
Listed to the left are the most relevant and most common Red Herring Fallacies. Many of the ones not listed are often used to dismiss difficult topics which most people would rather not engage with, or they can be applied so vaguely and arbitrarily that any meaningful discourse is usually shut down.
Red Herring Fallacies
Ad Hominem
- attacking the arguer instead of the argument

"Poor people are lazy, and that is why poverty exists."

"She is a stripper, so you shouldn't listen to what she says."
Red Herring Fallacies
Appeal to Authority -
when an argument relies too heavily on a single opinion

1. X is an authority on a topic
2. X says something about that topic
3. X is probably correct

"Sigmund Freud is an authority on psychoanalysis.
He says all women envy the male genitals.
Freud is probably right."
Straw Man
- an argument based on misrepresentation of an opponent's position

"People who are pro-choice want to use abortion as birth control."

"People who are pro-life don't care about children who are already born and are without proper guardians."

"Gun-control advocates love living in a police state."

A straw man argument is not simply
any
argument you have difficulty understanding; people often think that any argument which isn't immediately palatable is a straw man argument.
Begging the Question
- providing the conclusion as a premise, often in an indirect way to hide the fact

"To allow every man an unbounded freedom of speech must always be, on the whole, advantageous to the State, for it is highly conducive to the interests of the community that each individual should enjoy a liberty perfectly unlimited of expressing his sentiments."
Fallacy of Composition
- when one infers that something is true of the whole from the fact that it is true of
some part
of the whole

"If someone works hard, they can become rich.
Therefore, everyone should work hard to become rich."

"This metal won't break.
The machine is made of this metal.
Therefore, the machine won't break."
False Dilemma
- two alternative statements are held to be the only possible options, when in reality there are more

"Either you can vote for the Republicans or you can vote for the Democrats."

"Either you support war, or you hate freedom."

"Either you support Israel, or you're anti-semitic."
Formal and Informal Fallacies Review
Begging the Question


Affirming the Consequent


Appeal to Probablity


False Dilemma


Fallacy of Composition
When I fall down, I get a bruise. I have a bruise. Therefore, I fell down.

If I stand up at a ball game, I can see better. Everyone should stand up at ball games to see better.

The Spurs win most of their games; therefore, they will win tonight.

Free will exists because we make our own decisions freely.

You're either a man or a woman.
Red Herring Fallacies Review
Ad Hominem


Argumentum ad Populum


Straw Man


Appeal to Authority
Everyone knows that Columbus's crew thought the world was flat.


Kim Kardashian said that tweed skirts are in fashion; she is probably right.


Communists hate personal freedom.


She doesn't brush her teeth in the morning, so don't take her seriously.
Hasty Generalization



False Analogy



Cherry Picking


Faulty Generalizations Review
Faulty Generalizations
Cherry Picking
- suppressed evidence

"Hernán Cortés brought civility and the rule of law to the Americas. Because of his endeavors, several modern countries could flourish."
Hasty Generalization
- broad conclusion based on a small sample of information

"I passed through a town and saw only ten people, all of them children. Only children must live in that town."
Thank you and stop by the Writing Center!

Location: Dr. Billy F. Cowart Hall, 203
Phone: 956.326.2884
E-mail: writingcenter@tamiu.edu

Find us online!
Website: tamiu.edu/uc/writingcenter
Facebook: facebook.com/txamiu.writing
Twitter: twitter.com/tamiuwc
Pinterest: pinterest.com/tamiuwc

Appointments are welcome, but walk-ins are accepted.
TAMIU Writing Center
Like gold, brass is heavy and shiny. Gold is valuable. Brass must also be valuable.

Abraham Lincoln, a Republican, abolished slavery. Therefore, Republicans cannot be racist.


When I was in Ireland, I saw five black sheep but no white sheep. All sheep in Ireland must be black.


Informal Fallacies
Informal Fallacies
There are several common ways to commit
red herring fallacies
or
faulty generalizations
. They will be covered next.
Argumentum ad Populum
- a proposition is claimed to be true or valid because it is widely believed to be so

"Everyone knows Saddam Hussein was responsible for the attacks on September 11, 2001."

"Columbus 'discovered' America."
False Analogy
- noting the shared properties of two or more things and from this basis inferring that they also share some further property

"Computers from 1985 can display and compute data, like modern computers. Modern computers can display in color. Computers from 1985 must have also been able to display in color."
There are a multitude of subclassifications, but we will focus on just the four most common red herring fallacies:
Ad Hominem
Argumentum ad Populum
Appeal to Authority
Straw Man
Quick Tips to Avoid Fallacious Reasoning
Take an introductory logic course

If your argument "feels" shaky or unsound, it probably is

Research all aspects of your subject and arguments carefully and thoroughly

Have others read your work; ask someone to "play the devil's advocate"

Question yourself
constantly

Don't take anything for granted (don't
believe
anything)

Seek out dissenting opinions and identify what makes them strong/weak
= ?
Full transcript