Logical reasoning question types - Flaw in the reasoning que...

Learning Outcomes

By the end of this article, you will be able to identify and evaluate flaws in arguments presented in LSAT Logical Reasoning questions. You will understand the most common types of logical fallacies, recognize flaw question stems, and apply strategies to eliminate incorrect answer choices. You will also practice how to find parallel flaws and avoid common test errors, enhancing your ability to select the best answer on flaw-based LSAT questions.

LSAT Syllabus

For LSAT, you are required to understand argument evaluation and flaw detection in the Logical Reasoning section. When revising this area, focus on:

• recognising and describing common logical fallacies (e.g. correlation/causation, circular reasoning, hasty generalization)
• understanding how flaw questions are presented and how to spot them in the question stem
• identifying flaw types in arguments and explaining what is wrong with their reasoning
• using appropriate strategies for approaching flaw and parallel flaw questions on exam day

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which question stem below most likely signals a flaw question?
   1. "Which of the following, if true, most strengthens the argument?"
   2. "The reasoning in the argument is flawed because the argument..."
   3. "Which one of the following can be properly inferred from the statements above?"
   4. "Which of the following most accurately expresses the main point?"

2. What is the classic flaw when an argument assumes that because two events occur together, one causes the other?

3. True or false? On LSAT flaw questions, the correct answer always completely disproves the argument's conclusion.

4. What is the difference between a flaw and a necessary assumption in LSAT Logical Reasoning?

Introduction

When facing a Logical Reasoning flaw question on the LSAT, you must pinpoint what is wrong with the way an argument moves from its premises to its conclusion. Instead of strengthening or weakening an argument, you are describing the error in reasoning. Recognizing the argument’s flaw is critical for scoring well, as several questions in each Logical Reasoning section will assess this precise skill.

Key Term: flaw question
A question type that asks you to identify a mistake in the argument's logical reasoning that prevents the conclusion from being properly supported.

Flaw in the Reasoning: What Is Being Tested?

A flaw question requires you to spot an error in how the argument connects its evidence to its main claim. The tested skills include identifying classic logical fallacies, translating abstract answer choices, and matching flawed reasoning patterns in parallel flaw questions.

Flaw questions are commonly signposted by question stems such as:

• "The argument is most vulnerable to criticism on the grounds that it..."
• "Which one of the following most accurately describes a flaw in the argument's reasoning?"
• "A flaw in the reasoning of the argument is that..."

Types of Flaws Commonly Tested

The LSAT uses a set of recurring logical fallacies in its questions. Some of the most frequent are:

Key Term: logical fallacy
An error in reasoning that undermines the logic of the argument, often by making an unjustified assumption or leap.

Key Term: correlation/causation flaw
Assuming that because two things occur together or in sequence, one must cause the other, without eliminating other possible causes.

Key Term: circular reasoning
An argument that assumes its own conclusion as a premise, rather than providing independent evidence.

Key Term: hasty generalization
Drawing a broad or definitive conclusion from a limited or unrepresentative sample of evidence.

Key Term: ad hominem
Attacking the character or circumstances of the person making the argument, rather than addressing the merits of their position.

Key Term: false dichotomy
Presenting only two possible options or outcomes when others exist.

Key Term: equivocation
Using a word or phrase in more than one sense within the argument, creating a misleading connection.

Each of these can be described in abstract answer choices, so it’s important to be familiar with their characteristics.

Spotting Flaw Questions and Recognizing Flawed Reasoning

Most LSAT arguments contain a flaw or gap. Your task is to articulate, in the language of logic, what the gap is. Flaw questions often focus on these mistaken steps:

• Assuming causation from correlation.
• Mistaking necessary for sufficient conditions, or vice versa.
• Ignoring possible alternative explanations.
• Overgeneralizing from small or unrepresentative evidence.
• Attacking a person instead of responding to their argument.

Worked Example 1.1

A passage states:
"After a new transit system was introduced, the city saw a 30% drop in traffic accidents. Therefore, the transit system must have made the roads safer."

What is the flaw?

Answer:
The argument mistakes correlation for causation. There could be other reasons for the drop in accidents, such as new traffic laws or seasonal changes, not just the new transit system.

Worked Example 1.2

Argument:
"All the best tennis players train daily. Maria trains daily. Therefore, Maria is one of the best tennis players."

What is the flaw?

Answer:
The argument confuses necessary and sufficient conditions. While all the best players may train daily (training is necessary), training daily alone does not guarantee someone is among the best (not sufficient).

Tackling Flaw Questions on the Exam

To answer flaw questions efficiently:

1. Read the stimulus carefully and pinpoint the argument's conclusion and support.
2. Before reading the answers, use strict logic to identify any gaps or assumptions that might be unjustified.
3. Recognize abstract, generalized wording in answer choices and translate them into everyday reasoning.
4. Eliminate answers that do not address a genuine reasoning error.
5. Choose the answer that most directly describes how the argument fails to justify its conclusion.

Key Term: parallel flaw question
A variation of flaw question that requires you to identify another argument—among the answer choices—with reasoning that is flawed in the same way as the original argument.

Parallel Flaw Questions

Parallel flaw questions demand that you abstract the logical structure of the original flawed argument and match it to another scenario with the same mistake. This usually involves diagramming conditional statements or summarizing the pattern of reasoning.

Worked Example 1.3

Original:
"Whenever healthy pets eat Brand X food, they stay healthy. Fluffy is healthy, so she must have eaten Brand X."

Which of the following arguments contains a flaw most similar to the original?

(A) If a person eats fruit, they stay healthy. Mark is healthy, so Mark ate fruit.
(B) If a machine is maintained, it won’t break down. My laptop is working, so it must have been maintained.
(C) Only students who study pass the exam. Jane passed, so she must have studied.
(D) All cars that are washed shine. Mike’s car shines, so he must have washed it.
(E) If a contract contains errors, it is invalid. The contract is invalid, so it must have contained errors.

Answer:
Choice (D) is most similar in structure. Both arguments presume that the only way for a result to occur is via a specific cause, ignoring other possible ways for that result to arise.

Exam Warning

On LSAT flaw and parallel flaw questions, the most tempting wrong answer often describes a flaw that is actually not present in the argument. Focus on the exact logical jump made in the passage and do not be distracted by answer choices with similar but not identical flaws.

How to Translate Abstract Flaw Descriptions

Flaw answer choices may use abstract or technical language rather than concrete examples from the stimulus. Practice rewriting or matching abstract descriptions to common fallacies:

• "Takes for granted that... [hidden assumption]"
• "Fails to consider that... [ignored possibility]"
• "Mistakes correlation for causation."
• "Presumes what it sets out to prove." (circular reasoning)
• "Generalizes from a small or unrepresentative sample." (hasty generalization)

Revision Tip

Keep a list of common LSAT flaw "templates" in your notes and practice matching them to real question examples. This makes abstract answer choices much easier to translate on test day.

Summary

Table: Common Flaw Types, Their Abstract Descriptions, and How to Spot Them

Key Point Checklist

This article has covered the following key knowledge points:

• Flaw questions test your ability to identify errors in reasoning on the LSAT
• LSAT flaw questions use abstract answer choices that describe reasoning mistakes such as correlation vs causation, circularity, and overgeneralization
• Parallel flaw questions require you to match arguments with similar logical errors
• Recognizing flawed reasoning involves understanding the structure of arguments, not just their subject matter
• Translating abstract flaw descriptions into concrete reasoning is essential for success

Key Terms and Concepts

• flaw question
• logical fallacy
• correlation/causation flaw
• circular reasoning
• hasty generalization
• ad hominem
• false dichotomy
• equivocation
• parallel flaw question