Critical thinking: Fallacious reasoning(Fallacy = an error of reasoning)

Imants BreidaksMA History

Formal fallacies• Invalid syllogisms (deduction)• Hasty generalizations• This fallacy is committed when a person draws

a conclusion based on a sample that is not large enough. e.g. Smith, who is from England, decides to

attend graduate school at Ohio State University. He has never been to the US before. The day after he arrives, he is walking back from an orientation session and sees two white (albino) squirrels chasing each other around a tree. In his next letter home, he tells his family that American squirrels are white.

Fallacies of relevance.Ad Hominem (personal attack)

• Fallacies in which a claim or argument is rejected on the basis of some irrelevant fact about the author of or the person presenting the claim or argument.

Example Bill: "I believe that abortion is morally

wrong." Dave: "Of course you would say that, you're a priest." Bill: "What about the arguments I gave to support my position?" Dave: "Those don't count. Like I said, you're a priest, so you have to say that abortion is wrong. Further, you are just a lackey to the Pope, so I can't believe what you say."

Irrelevant appeals, special pleadings

• Appeals to: pity, tradition, authority, popularity, feare.g. "You know, Professor Smith, I really

need to get an A in this class. I'd like to stop by during your office hours later to discuss my grade. I'll be in your building anyways, visiting my father. He's your dean, by the way. I'll see you later." (fear)

Red Herring• Listener attempts to divert an arguer

from his argument by introducing another topic.e.g. “You may think that he cheated on

the test, but look at the poor little thing! How would he feel if you made him sit it again?”

Fallacies of ambiguity.Equivocation

• A term is used in two or more different senses within a single argument. e.g. The church would like to encourage

theism.Theism is a medical condition resulting from the excessive consumption of tea.Therefore the church ought to distribute tea more freely.

Fallacies of Presumption.Circular reasoning (begging

the question)• The premises include the claim that

the conclusion is true or (directly or indirectly) assume that the conclusion is true. e.g. Bill: "God must exist."

Jill: "How do you know." Bill: "Because the Bible says so." Jill: "Why should I believe the Bible?" Bill: "Because the Bible was written by

God."

False Dilemma• When someone is asked to choose

between two options when there is at least one other option available. e.g. Look, you are going to have to

make up your mind. Either you decide that you can afford this stereo, or you decide you are going to do without music for a while.

Post hoc ergo propter hoc• It is concluded that one event causes

another simply because the proposed cause occurred before the proposed effect. e.g. Jane gets a rather large wart on her finger.

Based on a story her father told her, she cuts a potato in half, rubs it on the wart and then buries it under the light of a full moon. Over the next month her wart shrinks and eventually vanishes. Jane writes her father to tell him how right he was about the cure.

Slippery Slope• False assumption that one thing

must lead to another e.g. "We've got to stop them from

banning pornography. Once they start banning one form of literature, they will never stop. Next thing you know, they will be burning all the books!"

Which fallacy?1. “We can either burn the house down

and collect the insurance money or we can continue living in an unsafe house. Since we shouldn’t keep living in an unsafe house, we should burn it down.”

Answer:

1. False dilemma

Which fallacy?2. “If we eat meat, then we disrespect

animals. If we disrespect animals, we will disrespect all forms of life. But if we disrespect all forms of life, we will begin killing other humans. Eventually, we will kill everyone. Therefore, no one should ever eat meat.”

Answer:

2. Slippery slope

Which fallacy?3. “This test is hard because it is so

difficult!”

4. If one does not weigh much, then one is light. Mark doesn’t weigh very much. Therefore, Mark is light. Thus, Mark cannot have dark skin.”

Answer: 3. Begging the question (circular

reasoning)

4. Equivocation

Which fallacy?5. “We can either go to the river or eat

sandwiches. We’re both hungry, so we should eat sandwiches and not go to the river.”

6. “Sally says I should drive a more fuel

efficient car, but her car gets even less mileage than mine; therefore, there is no reason for me to drive a more fuel efficient car.”

Answer:

5. False dilemma

6. Ad hominem

Which fallacy?7. The new UltraSkinny diet will make

you feel great. No longer be troubled by your weight. Enjoy the admiring stares of the opposite sex. Revel in your new freedom from fat. You will know true happiness if you try our diet!

Answer:

7. Appeal to emotions

Lateral thinking1. Deductive and inductive ways of

reasoning are essential for survival – problem solving

2 . Prison of consistency3. Edward de Bono – think outside the

box, come up with more creative ways of problem solving

Think “out of the box”1. A man lives on the twelfth floor of an

apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator -- or if it was raining that day -- he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up two flights of stairs to his apartment.

Answer:1. The man is a dwarf. He can't reach

the upper elevator buttons, but he can ask people to push them for him. He can also push them with his umbrella.

Think “out of the box”example2. A hunter aimed his gun carefully

and fired. Seconds later, he realized his mistake. Minutes later, he was dead.

Possible answers:2. It was winter. He fired the gun near

a snowy cliff, which started an avalanche.

He shot an elephant with a low caliber rifle. Not powerful enough to kill it, the elephant became enraged and trampled him.

Think “out of the box”example

3. A man is returning from Switzerland by train. If he had been in a non-smoking car he would have died.

Possible answer:3. The man used to be blind -- he's

returning from an eye operation which restored his sight. He spent all his money on the operation, so when the train (which had no internal lighting) goes through a tunnel, he thinks he's gone blind again and decides to kill himself. But before he could do it, he saw the light of the cigarettes people were smoking and realized he could still see.

Think “out of the box”example4. A man and his wife raced through

the streets. They stopped, and the husband got out of the car. When he came back, his wife was dead, and there was a stranger in the car, although no one had approached the car.

Possible answer:4. The wife was about to have a baby.

They drove to the hospital. The husband left to get a wheelchair, but the baby was born in the meantime, and the wife didn't survive the birth.

Think “out of the box”example5. A man is lying naked and dead, face

down in the desert. There's half a match near his outstretched hand.

Possible answer:5. He was with several others in a hot

air balloon, crossing the desert. The balloon was punctured, and they began to lose altitude. They tossed all their non-essentials overboard and then their clothing and food, but they were still sinking too fast. They drew matches to see who would jump over the side and save the others. This man lost.

Think “out of the box”example6. A man is wearing black. Black

shoes, socks, trousers, jumper, gloves and balaclava. He is walking down a black street with all the street lamps off. A black car is coming towards him with its light off too but some how manages to stop in time. How did the driver see the man?

Possible answer:

6. It was daytime

Think “out of the box”example7. A man died and went to Heaven.

There were thousands of other people there. They were all naked and all looked as they did at the age of 21. He looked around to see if there was anyone he recognized. He saw a couple and he knew immediately that they were Adam and Eve. How did he know?

Possible answer:7. He recognized Adam and Eve as the

only people without navels.. because they were not born of women, they had never had umbilical cords and therefore they never had navels.

“Change of perspective" technique - a problem-solving game

In small groups: • Try to come up with the most

unique (and perhaps coherent) new perspective: 1. Could there be a world where there

were no jobs? 2. What would morality be to a virus if it

had consciousness?

Bibliography:• Dunn, Wreen, M., 1989, “A bolt of fear,” Philosophy and

Rhetoric, 22: 131–40.• Dunn, Michael. Poor reasoning and fallacies (10th May

2013). theoryofknowledge.net. http://www.theoryofknowledge.net/ways-of-knowing/reason/poor-reasoning-and-fallacies/ Last accessed: 18th June 2016

• Fallacies. The Internet Encyclopedia of Philosophy. http://www.iep.utm.edu/fallacy/. Last accessed: 18th June 2016

• Fallacies. http://www.nizkor.org/features/fallacies/. Last accessed: 18th June 2016

• Informal Logic. http://www.informallogic.ca/. Last accessed: 18th June 2016

Thank you for your attention!