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The Top 15 Errors in Reasoning

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Good readers analyze the quality of written and spoken evidence and can spot fallacious reasoning. Thinking and reading critically will allow you to debunk faulty reasoning and improve your ability to argue effectively.

Get the FREE 15 Fallacious Reasoning essay e-comments, formatted for essay response. Set up to automatically insert into student essays in Microsoft Word and Google Docs.

1. Synonym Errors

A synonym reasoning error occurs when the writer substitutes one term for another in the argument, yet the terms are not same.

Example: The undemocratic government of Mexico had only one political party with real power. This dictatorship has been in control of Mexico since 1919.

Explanation: The writer substitutes dictatorship for undemocratic. However, not all undemocratic forms of government are the same as dictatorships.

2. Non Sequitur Errors

A non sequitur reasoning error means that the argument does not follow logically. In other words, the conclusion cannot be reached from the facts presented.

Example: If the sky is blue, and blue is the color of the ocean; then the sky must be made of ocean water.

Explanation: The conclusion that “the sky must be made of ocean water” does not follow logically from the facts presented.

3. Red Herring Errors

A red herring reasoning error means that an unconnected reference is used to distract the reader from the argument. A red herring refers to a smelly fish that was sometimes used to throw hunting dogs off the track of the fox in English foxhunts.

Example: The politician suggests that poverty remains the most important problem in the world today; however, the world has always had its share of poor people.

Explanation: The statement “the world has always had its share of poor people” attempts to distract the reader from the issue of poverty as the most important world problem.

4. Unsupported Generalization Errors

An unsupported generalization reasoning error applies specific facts to a broad generalization without justification.

Example: Bobby and Amanda have blonde hair. They both excel at sports. All blonde children excel at sports.

Explanation: The fact that specific children who have blonde hair are good athletes does not justify the broad generalization that “All blonde children excel at sports.”

5. Poisoning the Well Errors

A poisoning the well reasoning error means that an argument is weakened by a criticism in the argument itself.

Example: The president’s plan to reduce taxes in order to encourage taxpayers to spend more money to help business has been harshly criticized as “unworkable” by all leading economists.

Explanation: The president’s argument that reducing taxes will encourage taxpayers to spend more money is weakened by the comment that all leading economists have criticized the plan.

6. Cause and Effect Errors

A cause and effect reasoning error occurs when the writer assumes that something directly causes something else, but the result is actually a matter of coincidence.

Example: An irritating commercial aired after my favorite television show. I sneezed twice. Irritating commercials always make me sneeze.

Explanation: Sneezing after a commercial is a matter of coincidence. Commercials do not cause sneezing—there is no logical cause-effect connection.

7. Begging the Question Errors

A begging the question reasoning error takes place when the writer assumes something to be true, that has not been proven, in order to support the argument.

Example: No one likes the poor musicianship of country music.

Explanation: The statement assumes that country music has poor musicians to support the argument.

8. Either-Or Errors

An either-or reasoning error sets up a false choice between two ideas or issues and ignores other options.

Example: Either you support the president, or you are not a true American.

Explanation: The statement ignores other options that true Americans might choose.

9. Comparison Errors

A comparison reasoning error attempts to find similarities or differences between two unrelated ideas or issues.

Example: The price of Chinese tea has increased and so has the price of American gasoline.

Explanation: The price of tea and gas are unrelated issues and cannot be compared.

10. Questionable Authority Errors

A questionable authority reasoning error refers to a source that is not a specific expert on the idea or issue.

Examples: Experts say that the world will run out of oil in 20 years. A Harvard mathematician claims that love at first sight is impossible.

Explanation: In the first example, the expert is non-specific. In the second example, a mathematician is not an expert in matters of love.

11. Contradiction Errors

A contradiction error says the opposite of what has already been stated in the argument.

Example: Skateboarding is the safest of all individual sports. Skateboarding injuries account for more hospital visits than any other sport.

Explanation: Skateboard injuries contradict the claim that the sport is safe.

12. Inconsistency Errors

An inconsistency reasoning error refers to parts of an argument that are not in agreement.

Example: Children should be required to wear helmets while riding bicycles, but not while in-line skating.

Explanation: The arguments that children should be required to wear helmets while riding bicycles, but not while in-line skating, are not in agreement.

13. Omission Errors

An omission reasoning error means that a necessary piece of information is missing in the argument.

Example: The Folsom High School Band has the best band in the city.

Explanation: The fact that the Folsom High School Band is the only band in the city has been omitted.

14. Oversimplification Errors

An oversimplification reasoning error reduces a complicated idea or issue to something simple.

Example: Baseball is a simple game of pitching, running, hitting, and fielding.

Explanation: This oversimplification ignores the complicated components such as baseball strategy, substitutions, and statistical probability.

15. Sampling Errors

A sampling reasoning error refers to the data from which conclusions have been drawn. A sampling error may relate to an insufficient sample size or an unreliable sample group.

Example:  Three out of four dentists surveyed agree that people should floss twice per day.

Explanation: Only four dentists made up the sample group—hardly enough people upon whom to base a conclusion. Also, perhaps three of the dentists are paid by dental floss companies to promote their product.

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