Practice Identifying & Objecting to Informal Fallacies

© March 28, 2012 – May 21, 2012 James Wallace Gray

I will present 20 arguments. You can then figure out whether or not the argument contains an informal fallacy. If so, you can figure out what fallacy is presented, how to best object to it, and how create an argument map for your objection. I will then present my own answers. Keep in mind that my answers can legitimately differ from yours and many of the fallacies overlap.

Argument 1

1. If you eat one potato chip it won't hurt you.2. If you eat two or three potato chips, they won't hurt you.3. We can't draw the line concerning how many potato chips would be unhealthy to

eat.4. Therefore, it's never unhealthy to eat potato chips.

The above argument contains the continuum fallacy.

An objection to this argument is the following:

1. The above argument requires the assumption that “if we can't draw the line concerning how much of something we have to eat for it to be unhealthy, then it's never unhealthy.”

2. However, we know that eating too much candy is unhealthy and we don't know how to draw the line concerning how much candy we have to eat for it to be unhealthy.

3. If we know that eating too much candy is unhealthy and we don't know how to draw the line concerning how much candy we have to eat for it to be unhealthy, then something can be unhealthy even if we don't know how to draw the line concerning how much of it we have to eat for it to be unhealthy.

4. Therefore, the above argument requires a false assumption.

An argument map for the above objection is the following:

Argument 2

1. Medical scientists agree that it's generally healthy to drink water.2. If medical scientists agree that it's generally healthy to drink water, then it is.3. Therefore, it is generally healthy to drink water.

The above argument does not contain any informal fallacies. It is a non-fallacious appeal to authority.

Argument 3

1. There is no good evidence that dinosaurs still exist.2. If there is no good evidence that dinosaurs still exist, then they are probably

extinct (because we would expect to have found good evidence by now).3. Therefore, dinosaurs are probably extinct.

The above argument does not contain any informal fallacies. It isn't an appeal to ignorance because we would need evidence that dinosaurs still exist to reasonably believe they are no longer extinct.

Argument 4

1. The Higgs boson is a hypothetical elementary particle.2. We have not proven that the Higgs boson exists.3. If we have not proven that the Higgs boson exists, then it doesn't exist.4. Therefore, the Higgs boson doesn't exist.

The above argument contains a fallacious appeal to ignorance.

An objection to the above argument is the following:

1. The third premise is only true if things only exist that are proven to exist.2. There was a time before germs were proven to exist.3. If there was a time before germs were proven to exist, then it is false that things only exist that

are proven to exist.4. Therefore, the third premise is false.

An argument map for the above objection is the following:

Argument 5

1. Either dogs are mammals or reptiles.2. Dogs are not reptiles.3. Therefore, dogs are mammals.

The above argument contains no informal fallacies. It is not a false dilemma because no relevant options are missing.

Argument 6

1. The Sun rose above the horizon every day in human history.2. If the Sun rose above the horizon every day in human history, then the Sun will

probably rise tomorrow.3. Therefore, the Sun will probably rise tomorrow.

The above argument contains no informal fallacies. It doesn't contain a hasty generalization because this is a non-fallacious and reasonable kind of generalization.

Argument 7

1. Either humans are reptiles or humans are fish.2. Humans are not reptiles.3. Therefore, humans are fish.

The above argument contains a false dilemma.

We can object to the above argument in the following way:

1. The above argument requires that being reptiles or fish are the only two options for humans.2. However, humans could be mammals.3. If humans could be mammals, then the first premise is false.4. Therefore, the first premise is false.

An argument map for the above objection is the following:

Argument 8

1. Everyone has a family tree.2. If everyone has a family tree, then everyone has a pant with a long stem (because

trees are plants with a long woody stem or trunk).3. Therefore, everyone has a plant with a long woody stem or trunk.

The above argument contains an equivocation.

1. The above argument uses the word “tree” in two different ways.2. If the above argument uses the word “tree” in two different ways, then it's logically invalid.3. Therefore, the above argument is logically invalid.

We can support the second premise with the following argument:

1. An argument is logically invalid if another argument can use the same form, have true premises, and a false conclusion.

2. If the above argument uses the word “tree” in two different ways, then the argument form is “A; if B, then C; therefore C.”

3. “Everyone has a heart; a heart-shaped object is an object with a pointy end and two round shapes on the other end; therefore, everyone has an object with a pointy end and two round shapes on the other end” is an argument with the same form as the above argument, it has true premises, and a false conclusion.

An argument map for the above objection is the following:

Argument 9

1. Max argues that consensual polygamy among adults should be illegal because it hurts women.

2. However, there are consensual polygamous marriages between adults that don't hurt anyone.

3. If there are consensual polygamous marriages between adults that don't hurt anyone, then we have reason to think that these relationships don't hurt people.

4. Therefore, we have reason to believe that consensual polygamous relationships don't hurt people.

This argument does not contain any informal fallacies. It does not contain a straw man fallacy because Max's argument is not uncharitably described.

Argument 10

1. Victoria argues that capital punishment is wrong because human life has value.2. It seems that Victoria thinks that we should never kill people because human life

has value.3. However, we might have to kill people to protect ourselves and our loved ones in

self-defense.4. Therefore, Victoria is wrong that human life has value.

The above argument contains a straw man fallacy.

An objection to the above argument is the following:

1. The first premise is only true if it's impossible for human life to have value and for it to be morally right to kill a person.

2. It is possible for human life to have value and for it to be morally right to kill a person (because it could be morally right to kill a person who has value when necessary to save many other valuable lives).

3. Therefore, the first premise is false.

An argument map for the above objection is the following:

Argument 11

1. Killing people is always wrong.2. If killing people is always wrong, then killing people in self-defense is always

wrong.3. Therefore, killing people in self-defense is always wrong.

The above argument contains a begging the question fallacy.

The following is an objection to the above argument:

1. It's not always wrong to kill people when we have to do it to for self-defense.2. If it's not always wrong to kill people when we have to do it for self-defense, then it's false that

killing people is always wrong. 3. Therefore, the first premise is false.

An argument map for the above objection is the following:

Argument 12

1. If we have a dictatorship, then we can't hold the dictator accountable.2. If we can't hold the dictator accountable, then the dictator can abuse power.3. If the dictator can abuse power, then she can commit atrocities.4. We shouldn't let people commit atrocities.5. Therefore, we shouldn't have a dictator.

The above argument contains no informal fallacies. It doesn't contain a fallacious slippery slope because the implications discussed are justified.

Argument 13

1. Some white people committed crimes.2. Therefore, white people have unusual tendencies to be criminals.

The above argument contains the hasty generalization fallacy.

We can object to the above argument in the following way:

1. The above argument requires that we assume that it is impossible that some people from a racial group commit crimes without having unusual tendencies to be criminals.

2. However, some people from every racial group commits crimes.3. If some people from every racial group commits crimes, then it is possible that some people

from a racial group commit crimes without having unusual tendencies to be criminals.4. Therefore, the above argument requires a false assumption.

An argument map for the above objection is the following:

Argument 14

1. It's generally wrong to punch people.2. If it's generally wrong to punch people, then Cathy shouldn't punch people unless

she has a very good reason to do so.3. Cathy doesn't have a very good reason to punch a person when she's having a

pleasant conversation with that person.4. Therefore, it's wrong for Cathy to punch a person when she's having a pleasant

conversation with that person.

The above argument contains no informal fallacies. It doesn't contain the accident fallacy because the general rule is appropriately relevant to the argument.

Argument 15

1. If we legalize marijuana, then we will eventually legalize heroin.2. If we eventually legalize heroin, then we will eventually legalize human

sacrifice.3. We shouldn't legalize human sacrifice.4. Therefore, we shouldn't legalize marijuana.

The above argument contains the slippery slope fallacy.

An objection to the above argument is the following:

1. Premises that present controversial causal facts without presenting evidence for them are unjustified.

2. The first and second premises of the above argument present controversial causal facts without evidence for them.

3. The first and second premises are unjustified.

An argument map for the above objection is the following:

Argument 16

1. Elrond says we should vote for the Democratic party for president because they help the poor.

2. However, the Democratic candidate has used political power to violate human rights.

3. If the Democratic candidate has used political power to violate human rights, then we have an important consideration against voting for the Democratic candidate.

4. Therefore, we have an important consideration against voting for the Democratic candidate.

The above argument contains no informal fallacies. The above argument is not a red herring because the argument is relevant to Elrond's point.

Argument 17

1. Many medical professionals think there was a second gunman who helped assassinate John F. Kennedy.

2. If many medical professionals think something, then we should agree with them.3. Therefore, we should agree that a second gunman helped assassinate John F.

Kennedy.

The above argument contains the appeal to authority fallacy.

We can object to the above argument in the following way:

1. The second premise requires the assumption that medical professionals are experts regarding the Kennedy assassination.

2. However, medical professionals are not experts regarding the Kennedy assassination.3. Therefore, the second premise requires a false assumption.

An argument map for the above objection is the following:

Argument 18

1. The Republican candidate for president is wealthy.2. Therefore, we shouldn't vote for the Republican candidate for president.

The above argument contains the red herring fallacy.

We can object to the above argument in the following way:

1. The above argument requires the assumption that being wealthy disqualifies a person from being a qualified presidential candidate.

2. Thomas Jefferson was wealthy and was a qualified presidential candidate.3. If there is nothing about being a wealthy presidential candidate that disqualifies a person from

being a qualified person as a presidential candidate, then the assumption is false.4. Therefore, the above argument requires a false assumption.

An argument map for the above objection is the following:

Argument 19

1. We generally shouldn't kill people.2. Therefore, everyone who kills other people should be sent to prison.

Th above argument contains an accident fallacy.

We can object to the above argument in the following way:

1. The above argument requires the assumption that if we generally shouldn't kill people, then everyone who kills other people should be sent to prison.

2. However, if we generally shouldn't kill people, then some people who kill someone else because it's necessary for self-defense do nothing wrong.

3. If someone does nothing wrong, then that person should not be sent to prison.4. Therefore, the above argument requires a false assumption.

An argument map for the above objection is the following:

Argument 20

1. Lizards eat food, have legs, and have backbones.2. Mammals eat food, have legs, and have backbones.3. If lizards have more characteristics of mammals than reptiles, then they're

mammals.4. Therefore, lizards are mammals.

The above argument commits the one-sidedness fallacy.

We can object to the above argument in the following way:

1. If lizards are cold-blooded and lack mammary glands, then they have more characteristics of lizards than of mammals.

2. Lizards have more characteristics of reptiles than mammals.3. Therefore, the third premise is false.

An argument map for the above objection is the following: