Common Errors in Reasoning

Question 1

Internal Contradiction

Answer 1

An internal contradiction (also known as a self-contradiction) occurs when an author makes conflicting statements. (A form of error in the use of evidence.)

Question 2

Exceptional Case/Overgeneralization

Answer 2

This error takes a small number of instances and treats those instances as if they support a broad, sweeping conclusion. (A form of error in the use of evidence.)

Question 3

Lack of evidence for a position is taken to prove that position is false.

Answer 3

Just because no evidence proving a position has been introduced does not mean that the position is false. (An error in assessing the force of evidence.)

Question 4

Lack of evidence against a position is taken to prove that position is true.

Answer 4

Just because no evidence disproving a position has been introduced does not mean that the position is true. The lack of evidence against a position does not undeniably prove a position. (An error in assessing the force of evidence.)

Question 5

Some evidence against a position is taken to prove that the position is false.

Answer 5

The introduction of evidence against a position only weakens the position; it does not necessarily prove the position false. (An error in assessing the force of evidence.)

Question 6

Some evidence for a position is taken to prove that the position is true.

Answer 6

The introduction of evidence for a position only provides support for the position; it does not prove the position to be undeniably true. Partial support for a position does not make the position invincible. As you might expect, partial evidence for a position can be outweighed by evidence against that position. (An error in assessing the force of evidence.)

Question 7

Source Argument

Answer 7

Also known as ad hominem, this type of flawed argument attacks the person (or source) instead of the argument they advance. A source argument can take different forms, including focusing on the motives of the source, and focusing on the actions of the source.

Question 8

Circular Reasoning

Answer 8

In circular reasoning, the author assumes as true what is supposed to be proved. Often, a premise and conclusion are identical in meaning, whereas the conclusion should always follow from a premise. When the conclusion equally supports the premise, a “circular” situation emerges where you can move from premise to conclusion, and then back again to the premise, and so on.

Question 9

Mistaken Negation

Answer 9

Taking the absence of an occurrence as evidence that a necessary condition for that occurrence also did not take place.

Question 10

Mistaken Reversal

Answer 10

Mistakes being sufficient to achieve a particular outcome for being required to achieve it.

Question 11

Confuses a necessary condition for a sufficient condition

Answer 11

Confuses a sufficient condition for a necessary condition

Question 12

Mistaken Cause and Effect

Answer 12

Assuming a causal relationship on the basis of the (temporal) sequence of events; Assuming a causal relationship when only a correlation exists; Failure to consider an alternate cause for the effect, or an alternate cause for both the cause and the effect; Failure to consider that the events may be reversed.

Question 13

Straw Man

Answer 13

This error occurs when an author attempts to attack an opponent’s position by ignoring the actual statements made by the opposing speaker and instead distorts and refashions the argument, making it weaker in the process. In figurative terms, a “straw” argument is built up which is then easier for the author to knock down. Often this error is accompanied by the phrase “what you’re saying is” or “if I understand you correctly,” which are used to preface the refashioned and weakened argument.

Question 14

Appeal to Authority

Answer 14

An Appeal to Authority uses the opinion of an authority in an attempt to persuade the reader. The flaw in this form of reasoning is that the authority may not have relevant knowledge or all the information regarding a situation, or there may be a difference of opinion among experts as to what is true in the case.

Question 15

Appeal to Popular Opinion/Numbers

Answer 15

This error states that a position is true because the majority believe it to be true. Arguments are created by providing premises that support a conclusion. An appeal to popular opinion does not present a logical reason for accepting a position, just as an appeal based on numbers.

Question 16

Appeal to Emotion

Answer 16

An Appeal to Emotion occurs when emotions or emotionally-charged language is used in an attempt to persuade the reader.

Question 17

Survey Errors

Answer 17

The survey uses a biased sample (Certain types of people tend to respond to surveys more than others, or certain people are targeted to respond to surveys by those who created them); the survey questions are improperly constructed (If a survey question is confusing or misleading, the results of the poll can be inaccurate); Respondents to the survey give inaccurate responses (People do not always tell the truth when responding to surveys. If respondents give false answers to survey questions, the results of the survey are skewed and inaccurate).

Question 18

Error of Composition

Answer 18

This error occurs when the author attributes a characteristic of part of the group to the group as a whole or to each member of the group.

Question 19

Error of Division

Answer 19

This error occurs when the author attributes a characteristic of the whole (or each member of the whole) to a part of the group.

Question 20

Uncertain Use of a Term or Concept

Answer 20

As an argument progresses, the author must use each term in a constant, coherent fashion. Using a term in different ways is inherently confusing and undermines the integrity of the argument.

Question 21

False Analogy

Answer 21

An analogy is a comparison between two items. A False Analogy occurs when the author uses an analogy that is too dissimilar to the original situation to be applicable.

Question 22

False Dilemma

Answer 22

A False Dilemma assumes that only two courses of action are available when there may be others. Do not confuse a False Dilemma with a situation where the author legitimately establishes that only two possibilities exist.

Question 23

Time Shift Error

Answer 23

This error involves assuming that conditions will remain constant over time, and that what was the case in the past will be the case in the present or future.

Question 24

Relativity Flaw

Answer 24

This error occurs when information about a relative relationship – one involving a comparison – is used to draw an absolute conclusion, or when a relative conclusion is drawn from absolute information. While many arguments use comparisons improperly, there are many arguments which use them in a valid way, and thus the presence of a comparison does not automatically mean that the argument is flawed.

Question 25

Sunk Cost/Concorde Fallacy

Answer 25

This fallacy occurs when an argument is made that continuing the project or making additional investment is justified on the basis of past monies or efforts already invested (which may not be a good justification at all). The “sunk cost” portion of the name comes from the idea that the investment already made are basically costs that cannot be recovered without further effort; in other words, they have already been “sunk” into the project. The “Concorde” portion is a reference to the joint British-Drench project to create a supersonic jet, which was a massive boondoggle for taxpayers, and the program was continually justified on the basis of monies already spent (and because neither country wanted to lose face, a different sort of investment). Note that there can be instances where further investment is warranted, even if it were to come at a loss. For example, it might be needed to maintain customer good will or to signal to competitors that the company would follow through on its commitment. But in those instances, it’s not the past investment that justifies keeping the project alive, it’s the future returns that do so.

Question 26

General Lack of Relevant Evidence for the Conclusion

Answer 26

Some authors misuse information to such a degree that they fail to provide any information to support their conclusion or they provide information that is irrelevant to their conclusion. (A form of error in the use of evidence.)