LSAT LR Study Prep - Common Errors of Reasonings

Errors in the Use of Evidence

• When arguments contain errors in evidence, in failing to use information correctly.

• It has 4 types

General Lack of Relevant Evidence for the Conclusion

• A type of error in the use of evidence

• Some authors misuse information to such a degree that they fail to provide any relevant information to support their conclusion, or provide information irrelevant to their conclusion.

Lack of Evidence Against a Position is Taken to Prove That Position is True

• A type of error in the use of evidence

• Just because there is evidence disproving a position does not mean that the position is true.

• The lack of evidence against a position does not undeniably prove a position.

Some Evidence Against a Position is Taken to Prove that the Position is False

• A type of error in the use of evidence

• The introduction of evidence against a position only weakens it; it does not necessarily prove the position to be false.

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

• A type of error in the use of evidence

• The introduction of evidence that supports a conclusion does not automatically prove the conclusion is undeniably correct.

Source Argument

1. Aka ad hominem

2. This type of flawed argument attacks the person or the source instead of the argument they advance.

What are the Two forms that Source Arguments Can Take on?

1. Focusing on the motive of the source

2. Focusing on the actions of the source.

Circular Reasoning

1. These errors occur when the author assumes as true what is supposed to be proved.

2. The premise supports the conclusion, but the conclusion equally supports the premise, creating a “circular” situation where you can move from premise to conclusion.

Errors of Conditional Reasoning

1. Flaw in reasoning questions will ask you to describe Mistaken Reversal and Mistaken Negation in logical terms, specifically focusing on the common error of the two: confusing the sufficient condition for the necessary condition, and vice versa. 

Mistaken Cause and Effect

1. Because of the extreme basic causal assumption, arguments that draw causal conclusions are often flawed because there may be another explanation for the stated relationship.

2. There are 4 types

Assuming a causal relationship on the basis of the sequence of events.

• A type of mistaken cause and effect

• mistakes a temporal relationship for a causal relationship

Assuming a causal relationship when only a correlation exists.

• A type of mistaken cause and effect

• assumes a causal relationship where only correlation exists.

Failure to consider an alternate cause and effect, or an alternate cause for both the cause and the effect.

• A type of mistaken cause and effect

• fails to exclude an alternative explanation for the observed effect

Failure to consider that the events may be reversed

• A type of mistaken cause and effect

• The author mistakes an effect for a cause

Straw Man

This error occurs when an author attempts to attack an opponent’s position by ignoring the actual statements made by the opposing side and instead distorting and refashioning their arguments, thereby weakening them.

Appeal Fallacies

There are 3 main appeal fallacies:

1. Appeal to Authority

2. Appeal to Public Opinion/Numbers

3. Appeal to Emotion

Appeal to Authority

1. ⅓ of the fallacies.

2. Uses the opinions of authority in an attempt to persuade the reader.

3. The flaw of reasoning is that the authority may not have the relevant information or knowledge regarding a situation, or there is a difference in what experts say to what is true in the case.

Appeal to Public Opinion/Appeal to Numbers

1. ⅓ of the fallacies

2. This error states that a position is true because the majority believe it to be true.

3. An appeal to popular opinion does not present a logical reason for accepting a position, just an appeal based on numbers.

Appeal to Emotions

1. ⅓ of the fallacies

2. Occurs when emotions or emotionally charged language is used in an attempt to persuade the reader.

Survey Errors

1. Typically, LSAT makers believe survey data when conducted properly. Therefore, surveys are invalidated when:

   1. The survey uses a biased sample

   2. The survey questions are improperly constructed

   3. Respondents to the survey give inaccurate responses.

Errors of Division and Composition

These errors involve judgments made about groups and parts of groups.

Error of Composition

1. Occurs when the author attributes a characteristic of part of the group to the group as a whole.

2. From small to big

Errors of Division

1. Occurs when the author attributes a characteristic of the whole to a part of the group.

2. From big to small

Uncertain Use of a Term or Concept

1. Errors that occur when the author uses a term or concept in different ways within the stimulus, which confuses and undermines the integrity of the argument.

False Analogies

1. occurs when the author uses an analogy that is too dissimilar to the original situation to be applicable.

False Dilemmas

1. Dilemmas that assume that only two courses of action are available when there may be others.

2. Do not confuse a false analogy with a situation where the author legitimately establishes that only two possibilities are possible.

Time Shift Errors

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

2. What has occurred in the past is no guarantee that the future will be the same.

Relativity Flaw

1. Errors that occurs when information about a relative relationship—one involving a comparison—is used to draw an absolute conclusion.

Sunk Cost/Concorde Fallacy

1. Often seen in the finance and economics world.

2. The fallacy occurs when an argument is made that continuing in a project or making additional investments is justified because of past money or efforts already invested.

3. Just because you’ve invested in something, the return on investment may not justify finishing the project or further investments.

Numbers and Percentages Errors

1. Errors that occur when an author improperly equates a percentage with a definite quantity.