Fallaciesbad arguments that might look good

George W. Matthews

Pennsylvania College of Technology

Fall 2015

types of logical fallacies

1. fallacies of relevance

These have in common the use of irrelevantinformation to try to persuade us into believingthe conclusion.

2. fallacies of ambiguity

These rest on the multiple meanings that oftenare attached to individual words and concepts.

3. fallacies of presumption

These make additional unstated assumptions notwarranted by the context.

fallacies of relevance

appeal to authority

Experts say that drinking a glass of milk aday is the best way to lose weight. Thus itis a good idea to drink a glass of milk aday.

It is always a bad idea to trust someone just becausethey have the status of an expert. The experts mightbe right, but then don’t we need to see their evidence?

fallacies of relevance

appeal to authority

Experts say that drinking a glass of milk aday is the best way to lose weight. Thus itis a good idea to drink a glass of milk aday.

It is always a bad idea to trust someone just becausethey have the status of an expert. The experts mightbe right, but then don’t we need to see their evidence?

fallacies of relevance

ad hominem

Ms. X says that animals deserve rights.But we don’t have to listen to her sinceshe is wearing leather shoes.

Ad hominem means “against the person.” This is afallacy because it ignores what is being said andfocuses on who is saying it.

fallacies of relevance

ad hominem

Ms. X says that animals deserve rights.But we don’t have to listen to her sinceshe is wearing leather shoes.

Ad hominem means “against the person.” This is afallacy because it ignores what is being said andfocuses on who is saying it.

fallacies of relevance

popular appeal

The death penalty is supported by amajority of people. Therefore it is ajustified punishment.

Once again there is an irrelevant appeal made here tosomething that has no bearing on the truth of theconclusion. Just because many people believesomething does not by itself mean that they are correct.

fallacies of relevance

popular appeal

The death penalty is supported by amajority of people. Therefore it is ajustified punishment.

Once again there is an irrelevant appeal made here tosomething that has no bearing on the truth of theconclusion. Just because many people believesomething does not by itself mean that they are correct.

fallacies of relevance

appeal to force

Either my work is good enough for me topass this course or you are a dead man.

Yes, threats may get people to do what you want themto do, but they fail to provide reasons to believe whatyou are saying.

fallacies of relevance

appeal to force

Either my work is good enough for me topass this course or you are a dead man.

Yes, threats may get people to do what you want themto do, but they fail to provide reasons to believe whatyou are saying.

fallacies of relevance

appeal to consequences

If evolution is true, then we are all relatedto apes. But this is something I really don’tlike to admit. So evolution must be false.

Remember that the merely uncomfortableconsequences of a theory do not make that theoryfalse. Truth or falsity depends on evidence that directlybears on the case.

fallacies of relevance

appeal to consequences

If evolution is true, then we are all relatedto apes. But this is something I really don’tlike to admit. So evolution must be false.

Remember that the merely uncomfortableconsequences of a theory do not make that theoryfalse. Truth or falsity depends on evidence that directlybears on the case.

fallacies of relevance

naturalistic fallacy

Women alone are capable of gettingpregnant and having babies. Therefore usmen should not be responsible for changingdiapers.

The premise is about the facts of human nature and isclearly true. But the conclusion is about somethingvery different – the question of social roles which areup to us to create as we see fit. Hence appealing tonature here is irrelevant.

fallacies of relevance

naturalistic fallacy

Women alone are capable of gettingpregnant and having babies. Therefore usmen should not be responsible for changingdiapers.

The premise is about the facts of human nature and isclearly true. But the conclusion is about somethingvery different – the question of social roles which areup to us to create as we see fit. Hence appealing tonature here is irrelevant.

fallacies of relevance

red herring

That guy claims that animals have rights.Well he should consider doing somethingmore to protect humans. After all, thereare plenty of people who are in need ofprotection from tyranny and abuse.

This fallacy gets its name from a tactic used to throwoff bloodhounds – wipe a (reddish colored) piece ofsmoked fish across the trail and toss it into the bushesnearby. Changing the subject is not arguing fairly.

fallacies of relevance

red herring

That guy claims that animals have rights.Well he should consider doing somethingmore to protect humans. After all, thereare plenty of people who are in need ofprotection from tyranny and abuse.

This fallacy gets its name from a tactic used to throwoff bloodhounds – wipe a (reddish colored) piece ofsmoked fish across the trail and toss it into the bushesnearby. Changing the subject is not arguing fairly.

fallacies of relevance

weak analogy

Asking me to pay taxes is like asking me tolet you steal money directly from bybanking account, and that’s just not right!

We should be careful with our use of analogies,especially when one of the terms has very strongemotional content. A weak analogy is one whererelevant differences between two analogous things areignored.

fallacies of relevance

weak analogy

Asking me to pay taxes is like asking me tolet you steal money directly from bybanking account, and that’s just not right!

We should be careful with our use of analogies,especially when one of the terms has very strongemotional content. A weak analogy is one whererelevant differences between two analogous things areignored.

fallacies of ambiguity

equivocation

If you can think whatever you want, youare really free. People in jail can thinkwhatever they want. So they should stopwhining about wanting to be free.

Note the change in meanings of the word “free” here.To equivocate is to confuse multiple different meaningsof a word with each other.

fallacies of ambiguity

equivocation

If you can think whatever you want, youare really free. People in jail can thinkwhatever they want. So they should stopwhining about wanting to be free.

Note the change in meanings of the word “free” here.To equivocate is to confuse multiple different meaningsof a word with each other.

fallacies of ambiguity

straw person

By asking for us to withdraw our troopsfrom that country those hippies are sayingwe shouldn’t ever defend ourselves fromattack!

We should always be careful to avoid creating acaricature of any position we oppose. Such a viewmight be easy to knock down but if we are after thetruth, misrepresenting other viewpoints does not get usany closer to it.

fallacies of ambiguity

straw person

By asking for us to withdraw our troopsfrom that country those hippies are sayingwe shouldn’t ever defend ourselves fromattack!

We should always be careful to avoid creating acaricature of any position we oppose. Such a viewmight be easy to knock down but if we are after thetruth, misrepresenting other viewpoints does not get usany closer to it.

fallacies of presumption

mere assertion

There are simply no grounds for believingthat global warming is caused by humans.

Is there even a reason given here?

fallacies of presumption

mere assertion

There are simply no grounds for believingthat global warming is caused by humans.

Is there even a reason given here?

fallacies of presumption

begging the question

You should be a Christian. After all, theBible says that you will go to Hell if youare not a Christian.

We beg the question whenever we assume in thepremises of our argument the very question we areclaiming to prove. This is also known as “preaching tothose already converted.”

fallacies of presumption

begging the question

You should be a Christian. After all, theBible says that you will go to Hell if youare not a Christian.

We beg the question whenever we assume in thepremises of our argument the very question we areclaiming to prove. This is also known as “preaching tothose already converted.”

fallacies of presumption

appeal to ignorance

Nobody has ever proven that the deathpenalty deters crime. It is most likely noteven possible to prove this. Thus it doesnot deter crime.

To quote from Dick Cheney – “lack of evidence is notevidence of a lack.” Just because we do not knowsomething does not mean we are entitled to concludethat it is false.

fallacies of presumption

appeal to ignorance

Nobody has ever proven that the deathpenalty deters crime. It is most likely noteven possible to prove this. Thus it doesnot deter crime.

To quote from Dick Cheney – “lack of evidence is notevidence of a lack.” Just because we do not knowsomething does not mean we are entitled to concludethat it is false.

fallacies of presumption

false dilemma

Either you agree with me that DonaldTrump would be a great president or youare a communist. Since you do not agreewith me, you are clearly a communist.

In spite of its popularity in political campaigns thisargument strategy clearly doesn’t work – how manyother possibilities are just not mentioned? Anothername for this fallacy is the “black or white fallacy.”

fallacies of presumption

false dilemma

Either you agree with me that DonaldTrump would be a great president or youare a communist. Since you do not agreewith me, you are clearly a communist.

In spite of its popularity in political campaigns thisargument strategy clearly doesn’t work – how manyother possibilities are just not mentioned? Anothername for this fallacy is the “black or white fallacy.”

fallacies of presumption

hasty generalization

Most people are against raises taxes tofund public transportation. After all 95percent of my friends are.

It is possible to legitimately generalize from a samplingof data from a larger set, but only if you take steps toavoid a biased sample.

fallacies of presumption

hasty generalization

Most people are against raises taxes tofund public transportation. After all 95percent of my friends are.

It is possible to legitimately generalize from a samplingof data from a larger set, but only if you take steps toavoid a biased sample.

fallacies of presumption

slippery slope

If we legalize physician assisted suicide oreuthanasia, anyone over 60 had betterwatch their backs.

This fallacy involves arguing against somethingrelatively uncontroversial by highlighting a possible, buthighly improbable, and highly undesirable consequence.What is the mechanism that would propel us down theslippery slope? Often it is not spelled out.

fallacies of presumption

slippery slope

If we legalize physician assisted suicide oreuthanasia, anyone over 60 had betterwatch their backs.

This fallacy involves arguing against somethingrelatively uncontroversial by highlighting a possible, buthighly improbable, and highly undesirable consequence.What is the mechanism that would propel us down theslippery slope? Often it is not spelled out.

fallacies of presumption

false cause

Two days ago I had a bad cold. Then Idrank a bottle of whiskey. Thus whiskeymust cure colds.

This fallacy confuses correlation with causation and isespecially popular among peddlers of remedies for adisease that has no cure – the common cold. It is alsoknown by the fancy Latin name: post hoc, ergo propterhoc, which translates as “after which, thereforebecause of which.”

fallacies of presumption

false cause

Two days ago I had a bad cold. Then Idrank a bottle of whiskey. Thus whiskeymust cure colds.

This fallacy confuses correlation with causation and isespecially popular among peddlers of remedies for adisease that has no cure – the common cold. It is alsoknown by the fancy Latin name: post hoc, ergo propterhoc, which translates as “after which, thereforebecause of which.”

fallacies of presumption

circular reasoning

He definitely did it, since he has a guiltylook on his face. And it is clear that it is aguilty look, since he is the one who did it.

Which is the premise here and which is the conclusion?Both and neither since the first leads to the secondwhich leads to the first. Round and round we go.

fallacies of presumption

circular reasoning

He definitely did it, since he has a guiltylook on his face. And it is clear that it is aguilty look, since he is the one who did it.

Which is the premise here and which is the conclusion?Both and neither since the first leads to the secondwhich leads to the first. Round and round we go.

For more types of fallacies and many moreexamples, check out the links below. Orpick up any newspaper.