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informal_fallacies.pptxPHIL 105-010 January 26th, 2016
Informal Fallacies
Please Note
The examples of fallacies are given in italics.
The explanations are in plain text.
You are welcome to go online to look for more examples.
You will be tested on these fallacies.
There is a practice quiz at the end.
Informal Fallacies
Informal Fallacies are errors in informal or casual reasoning.
They are often committed in casual conversation.
But you can also find them in the media.
People are often unaware that they are committing an informal fallacy.
Committing an informal fallacy often reveals what our reality and value assumptions are.
#1 Fallacy of Composition
When the attribute of an individual or part of something is attributed to the whole or group.
The cells in my body are round; therefore my body is round.
False. The attribute of a cell (roundness) cannot be attributed to what those cells make up, i.e., the body.
The cup holder in my car is made of plastic; therefore, my car is made of plastic.
#2 Fallacy of Division
The opposite of the fallacy of composition.
The idea that an attribute of the whole can be applied to the individual parts of that whole.
Drexel is an old university; therefore, all the professors are old.
False. The attribute of the whole (Drexel is old) cannot be applied to what makes up Drexel (for example, the professors).
The earth is round; therefore, all earthlings are round.
#3 Circular Reasoning
When the conclusion you arrive at is actually already present in your premises (the ideas you believe support your conclusion).
It appears as if you are repeating yourself.
There’s only survival of the fittest because only the fittest survive.
What the Bible says is true because the Bible is true (or because the Bible says so).
#4 Loaded Question
When you ask someone a question to which there is no good answer and the other person cannot extricate themselves
Have you stopped beating your wife yet?
If you says yes, you are still beating your wife.
If you say no, it means you admit to once beating your wife.
There is no way to win.
Are you stoned or stupid?
These are usually rhetorical questions.
#5 Naturalistic Fallacy
That because something is the case in nature it ought to be the case, usually among humans.
This is taking a reality assumption and converting it into a value assumption.
Swans are monogamous; therefore, humans should be monogamous.
Bonobos are promiscuous; therefore, humans should be promiscuous.
Fish swim; therefore, humans should swim.
#6 cum hoc ergo propter hoc
Also known as “correlation = causation”
However, correlation does not equal causation
Children who wear big shoes also have good handwriting. Therefore, wearing big shoes causes good handwriting.
No, wearing big shoes does NOT cause good handwriting. These things are merely correlated.
This is how superstitions can start.
Because I wore those red socks, I hit the home run. Those are my lucky red socks.
#7 Fallacy of Accident
In the process of reasoning, a missing condition causes a faulty conclusion.
Cutting people with knives is a crime. →
Surgeons cut people with knives. →
Surgeons are criminals.
This is false because there is a missing condition: i.e., surgeons are cutting people as part of medical treatment. Criminals are not.
#8 False Dilemma
When you are asked to make a choice between two things despite the fact that a third (or even fourth) option exists
You are either for us or against us
No, I may agree with you on some things and disagree with you on others
Either love me or hate me
No, I simply want to like you
Are you stoned or stupid?
No, I have a cold, and I am taking cold medicine. (Note how this question can also be viewed as a loaded question.)
#9 post hoc ergo propter hoc
A happened before B, therefore A caused B
This is also how superstitions start
After I saw that black cat, I lost my job. Therefore, seeing the black cat caused me to lose my job.
Hence the idea of “bad luck”.
The train arrives after the people all get there.
No, the arrival of the people at the train station does not cause the train to come.
# 10 False Analogy
Analogy: A/B as C/D
A is analogous to C and B is analogous to D
In order to build this country we had to kill a few Indians, but you can’t make an omelet without breaking a few eggs.
Are (dead) Indians analogous to eggs?
Is a nation analogous to an omelet?
NO. It is necessary by definition to break eggs to make an omelet; it is not necessary to kill Indians to make a nation.
Employees are like nails. Just as nails must be hit in the head in order to make them work, so must employees.
Notice that this is also an example of equivocation. A human head is not like the head of a nail.
#11 Affirming the Consequent
To suppose that because A implies B that B implies A
Many drunks people are poor (A implies B); therefore, many poor people are drunks (B implies A).
No. This is not the case.
Many mammals have four legs; therefore, things with four legs are mammals.
No. Consider a table or a lizard.
My dog likes to chase the cat; therefore, the cat likes to chase my dog.
#12 Retrospective Determinism
The belief (as seen in hindsight) that because something happened the way it did, it was bound (determined or predetermined) to happen that way.
The minute Jimi Hendrix picked up a guitar he was destined to become a superstar.
No. Jimi could have picked up a guitar and become a mailman. Many things besides picking up that guitar led him to become a superstar.
Just as soon as Kennedy became President, you just knew he was going to get shot. (No, you didn’t.)
#13 Hasty Generalization
Jumping to conclusions. This is common in statistics when people make conclusions based on a very small sample size.
I saw my wife talking to another man. Therefore, she must be having an affair.
No. Maybe they were just having a conversation. Here you can see how reality assumptions color the conclusions that we come to.
My friend Luigi likes to eat mussels. Therefore, (all) Italians like to eat mussels.
One person is a very small sample size to come to a conclusion about a whole population.
# 14 False Compromise
This is the opposite of false dilemma.
It is to come to some middle ground on what is essentially a binary matter.
When it couldn’t be agreed upon whether slaves were fully human or not, it was agreed that slaves were 3/5 human.
See http://en.wikipedia.org/wiki/Three-Fifths_Compromise
We need to cross a 40’ chasm, so let’s build a 20’ bridge, and we’ll be half way there.
Um…no.
#15 Slippery Slope
This is to start with a premise and run through a long list of other ideas, finally reaching a conclusion that is absurd.
If you go to the party, you’ll meet a boy, and if you meet a boy, you’ll kiss the boy, and if you kiss the boy, you’ll have sex with the boy, and if you have sex with the boy, you’ll get pregnant, and if you get pregnant, you won’t go to college, and if you don’t go to college, you won’t get a good job. So, you can’t go to the party because you won’t get a good job.
#16 Strawman “Argument”
This is when Person A makes a statement and Person B tries to contradict Person A’s statement by talking about something else or twisting A’s position.
It’s “pulling a fast one.”
Person A: I think universal healthcare is a great idea.
Person B: Universal healthcare is for welfare recipients, and everybody knows people on welfare won’t work. So why should we as a nation support universal healthcare for people who won’t work?
Notice that Person B has not actually addressed the issue of universal health care but has deflected Person A’s statement by talking about welfare recipients.
#17 Equivocation
When someone advances an argument by accidentally or deliberately using two different meanings of the same word. In other words, the person is depending on ambiguity.
Feathers are light.
Light is the opposite of darkness.
Therefore, feathers are the opposite of darkness.
No. In the first case, the word light is used in reference to weight. In the second case, light refers to what the sun and light bulbs produce.
Practice Quiz Name that Fallacy
1. Maria is fair. Fair people are just. Therefore, Maria is a just person.
2. After the meteor hit, everyone in the village got sick. Therefore, the meteor caused the sickness.
3. Every time I wore my hat to a Penn State game, Penn State won. Therefore, my hat caused Penn State to win.
4. Are you just being rude or are you trying to convince me that you’re stupid?
5. The planets go around the sun like electrons in an atom. Therefore, planets can jump out of their orbits like electrons jump out of their orbits.
Practice Quiz Name that Fallacy continued
6. Wolves eat raw meat in the wild; therefore, dogs ought to eat raw meat.
7. The team is good; therefore, every member of the team is good.
8. The reason opium puts you to sleep is because it’s a soporific.
9. Once Caesar became Emperor, there was no way he could avoid being assassinated.
10. Marijuana is a drug, and it’s illegal. Xanax is a drug. It should be illegal, too.
Practice Quiz Answers
1. Equivocation (fair)
2. post hoc ergo propter hoc (after)
3. cum hoc ergo propter hoc (when)
4. False dilemma OR loaded question
5. False analogy
6. Naturalistic fallacy
7. Fallacy of division
8. Circular reasoning (soporific means ‘puts to sleep’)
9. Retrospective determinism
10. Equivocation (drug)
