Formal Reasoning Patterns
and Formal Fallacies

Reliable:

Affirming the Antecedent
Denying the Consequent
Disjunctive Syllogism

Fallacious:

Affirming the Consequent
Denying the Antecedent
Disjunctive Fallacy

Fallacies of Relevance

Argument from Ignorance

Appeal to Authority

Argument Against the Person (ad hominem)

Appeal to the People (to Emotion)

Appeal to Pity

Appeal to Fear (to Force)

Argument from Ignorance

The National Toxicology Board may take saccharine off the list of probable cancer-causing compounds. The original evidence linking saccharine involved lab rats who developed tumors in the bladder. Researchers now think the saccharine precipitated in the rats' bladders as crystals and that the crystals irritated the bladder and caused the tumors. Humans do not consume saccharine in sufficient amounts to produce the crystals, and no study on humans has shown a link between saccharine and cancer. But opponents argue that just because saccharine does not produce cancer in humans through one mechanism, we don't know that it doesn't produce cancer in humans through another mechanism. Thus, they say, saccharine should not be 'delisted'.

National Public Radio, Oct. 30, 1997

Appeal to Authority

It is a fallacy to accept some claim because a putative authority has been cited in support of the claim if the person cited is really not an authority in the matter at hand.

But an appeal to authority can constitute a fallacy even when the authority really is an authority in the matter at hand. This happens when one refuses to consider any evidence for a claim just because some authority rejects the claim.

Example: Galileo claims to have seen bodies revolving around Jupiter. On this and other supposed evidence, Copernicus concludes that the planets, including the earth, revolve about the sun. This is surely false. Aristotle, Ptolemy, and other authorities on natural philosophy say the earth is the center of the universe and all heavenly bodies move about it.

Argument Against the Person

(Ad Hominem)

Ambassador to Iraq Ryan Hooker says that reports gathered by independent sources show that the the incidence of violent attacks in Iraq has gone down significantly since the surge in troops. But that is just what you would expect from a representative of the Bush administration.

Appeal to the People

Congress and the country supported initiating a war against Iraq based on intelligence indicating that Iraq had weapons of mass destruction and contributed to the attacks on the U.S. on September 11, 2001. That intelligence has now been shown to be faulty. But polls show that a large majority of Americans still believe that Iraq had WMDs and was involved in the 9/11 attacks. So after all, our move to remove Sadam Hussein from power in Iraq was justified.

Appeal to Pity

George has not done very well in this course. But if he doesn't receive at least a B, he will lose his Hope Scholarship. So I have decided to give him a B for the course.

Appeal to Force

Senator and Presidential candidate Barach Obama is speaking at the Student Center this evening at 7:00 this evening. I plan to be there, and I hope all of you will be there, too. I will take note of which students in the class are at this political rally. I know all of you want to make a good grade in this class.

Fallacies of Presumption
(Unwarranted Assumption)

Complex Question

False Cause

Begging the Question (Circular Argument)

Accident

Hasty Generalization (Inadequate Sample, Inappropriate or Atypical Sample)

False Dilemma

This is an example of a valid survey question.

Which of the following best represents your attitude toward Clinton's deposition in the Paula Jones case.

A. He committed perjury and should have been removed from office.

B. He committed perjury and should have been censured, but not removed from office.

C. If he committed perjury, it was only about his personal sex life and isn't that important.

D. He didn't commit perjury.

E. No opinion.

Complex Question

This survey question commits the fallacy.

Which of the following best represents your attitude toward Clinton's perjury in the Paula Jones case.

A. He should have been removed from office.

B. He should have been censured, but not removed from office.

C. It's not that important and it has already received too much attention.

D. No opinion.

Rhetorical Question (This is NOT a fallacy!)

During the period 1987-1997, the University saw tremendous improvement in its facilities. New buildings included the Biological Sciences Center, the additions to the law school and the business school, and all of east campus including a new Student Health Center, an Animal Sciences Building, the Fine Arts Complex, the Ramsey Student Activity Center, and the East Parking Deck. And who was President of the University during this period? We owe Dr. Charles Knapp a big "Thank you!"

Complex Question

Respond the to following statements by circling a number between 1 and 5 where 5 means you strongly agree with the statement and 1 means you strongly disagree with the statement.

1. Bill Clinton's unethical involvement in the Whitewater business deal is a good reason to vote against him. (Fallacy)

2. We should pass a Constitutional amendment to stop the murder of unborn babies. (Fallacy)

3. This is an excellent course.

False Cause

My car misfires whenever I buy gas from the station on the corner. It never misfires when I buy gas somewhere else. I think the gas at the corner station causes my car to run badly.

Since I started giving Mary a ride to school everyday, my car has been misfiring. I think Mary causes my car to run badly.

Begging the Question
(Circular Argument)

Women should not get abortions because an unborn fetus is nevertheless a person, and destroying the life of any person is wrong.

Women should not get abortions because it is wrong to terminate a viable fetus. (Fallacy)

Accident

Birds fly. John's new pet is a bird. So John's new pet can fly.

Birds fly. John's new pet is a penguin, and penguins are birds. So John's new pet can fly.(Fallacy)

Bob was late for class. So he parked in a handicap space. He should be given a ticket.

That woman in a wheelchair parked in a handicap space. She should be given a ticket. (Fallacy)

Hasty Generalization
(Atypical Sample)

Americans overwhelmingly support access to abortions for women. The National Organization for Women recently conducted a survey of its 250,000 members. Over 90% responded to the questionnaire distributed by NOW, and over 90% of those responding said safe, legal abortions should be available to women who want them. (Fallacy)

Hasty Generalization

Which one is a fallacy and why?

The CDC conducted a study of people with high cholesterol. They randomly divided them into two groups of 100. One group was given a cholesterol-lowering medication for ten years and the other was given a placebo for the same period. At the end of the study, the group taking the medication had experienced 45% fewer heart attacks. These new drugs are an effective weapon in fighting heart disease.

The CDC studied two people with high cholesterol. One person was given a cholesterol-lowering medication for ten years and the other was given a placebo for the same period. At the end of the study, the person taking the medication had experienced 45% fewer heart attacks. These new drugs are an effective weapon in fighting heart disease. (Fallacy)

False Dilemma

If you go to college, you'll depend on your father for tuition and living expenses. If you work for your father's company, you will depend upon your father for your salary. You can either work for your father's company or go to college. So you are going to remain dependent on your father. (Fallacy)

If you study, you won't have time to party. If you don't study, your parents will cut off your allowance and you won't have the money to party. Either you study or you don't. So college isn't going to be as much fun as you thought.

Smith either stays away from his former partner in crime, Jones, or he violates the conditions of his parole. If he violates parole, he will go back to prison. He doesn't want to go back to prison; so Smith should stay away from Jones.

Fallacies of Ambiguity

Equivocation

Amphiboly

Composition

Division

Amphiboly

Nothing is better than happiness. A ham sandwich is better than nothing. So a ham sandwich is better than happiness.

B is better than C. A is better than B. So A is better than C.

It isn't true that there is something better than happiness. It is better to have a ham sandwich than not to have anything. So it is better to have a ham sandwich than to be happy.

Amphiboly

1. If you know something, then it must be true.

2. If you know Bill Clinton won the Presidential election in, then it must be true that Clinton won.

4. But if something must be true, then nothing could have happened that would make it false.

5. But since Clinton could have lost, you don't know that he won.

A. Necessarily (If you know something, it is true.)

B. If you know something, then it is necessarily true.

Equivocation

In order to be a craftsman, a person must serve the interest of the subject matter of his or her craft. For example, a potter must produce good and serviceable pots and a doctor must maintain the health of his patient. The subject matter of ruling is the ruled. So the ruler must serve the interests of the ruled.

A moral person is one who lives well. If a person lives well, then he or she is happy. So a moral person is happy.

Plato, The Republic

Composition

Each state in the United States has established educational standards. So like the Western European countries, the United States also has national standards for its educational system.

Division

The United States is one of the richest countries in the world. You are a citizen of the United States. So you must be rich.

Alternative names for fallacies

Appeal to the people, popular sentiment,
ad populum

Appeal to pity, appeal to sympathy,
ad misericordiam

Appeal to force, ad bacculum

Attack on the person, ad hominem

False cause,
post hoc, ergo propter hoc

False dichotomy, false dilemma

Weak analogy, false analogy

Page last updated:
Send email to Donald Nute