Deconstructing LSAT Logical Reasoning: Common Logical Fallacies
The Logical Reasoning section of the LSAT is designed to test your ability to analyze arguments, identify assumptions, and evaluate reasoning. A crucial component of mastering this section is understanding common logical fallacies – errors in reasoning that weaken or invalidate an argument. Recognizing these fallacies is key to deconstructing arguments effectively and choosing the correct answer on the LSAT.
What are Logical Fallacies?
A logical fallacy is a flaw in the structure of an argument that makes it invalid or unsound. These flaws can be subtle and are often used intentionally in persuasive rhetoric, but on the LSAT, they are presented as errors in reasoning that you need to identify. Understanding fallacies helps you pinpoint weaknesses in an argument, predict the correct answer choices, and avoid falling for deceptive reasoning.
Key Common Logical Fallacies on the LSAT
Specific Fallacies and Their Identification
| Fallacy Name | Description | LSAT Clue/Example |
|---|---|---|
| Ad Hominem | Attacking the person making the argument rather than the argument itself. | Focuses on character, motives, or personal traits instead of the argument's logic. |
| Straw Man | Misrepresenting an opponent's argument to make it easier to attack. | Distorts or exaggerates the original claim to create a weaker version to refute. |
| False Cause (Post Hoc Ergo Propter Hoc) | Assuming that because one event followed another, the first event caused the second. | Correlation is mistaken for causation; 'After X, therefore because of X.' |
| Hasty Generalization | Drawing a conclusion based on a small sample size, rather than looking at statistics that are much more in line with the typical or average situation. | Jumping to a broad conclusion from insufficient evidence. |
| Appeal to Authority | Claiming something is true because an authority figure (who may not be an expert in the relevant field) says it is. | Relies on the word of an unqualified or irrelevant authority. |
| False Dichotomy (Either/Or) | Presenting only two options or sides when there are actually more. | Forces a choice between two extremes, ignoring middle ground or alternatives. |
| Circular Reasoning (Begging the Question) | The argument's conclusion is used as one of its premises. | The premise assumes the truth of the conclusion, leading to a loop. |
| Slippery Slope | Asserting that a relatively small first step will inevitably lead to a chain of related events culminating in some significant (usually negative) effect. | Suggests an extreme chain reaction without sufficient evidence. |
Strategies for Identification
When encountering an argument on the LSAT, actively look for these patterns. Ask yourself: Does the conclusion logically follow from the premises? Is the evidence sufficient? Is the argument attacking the idea or the person? Are there unstated assumptions that are not justified? Practice identifying these fallacies in real-world examples and LSAT-style questions to build your recognition skills.
Think of fallacies as 'red flags' in an argument. They signal a weakness that you can exploit to find the correct answer.
To pinpoint weaknesses in an argument and select the correct answer choice.
Practice Makes Perfect
The best way to master logical fallacies is through consistent practice. Work through official LSAT prep materials, focusing on questions that ask you to identify flaws in reasoning, strengthen or weaken arguments, and make inferences. Pay close attention to the explanations for why certain answer choices are correct and others are incorrect, especially when fallacies are involved.
Visualizing the structure of an argument can help in identifying fallacies. Imagine an argument as a bridge. The premises are the pillars, and the conclusion is the deck. A fallacy is like a weak or broken pillar, or a deck that doesn't connect properly to the pillars, making the entire structure unstable. For example, a 'hasty generalization' is like building a bridge with only one tiny, unstable pillar – it can't support the weight of the conclusion. An 'ad hominem' attack is like trying to fix a broken pillar by painting it a different color; it doesn't address the structural issue.
Text-based content
Library pages focus on text content
Learning Resources
A clear and concise guide to common logical fallacies with simple explanations and examples.
An in-depth explanation of common fallacies specifically as they appear on the LSAT, with LSAT-specific examples.
A comprehensive academic overview of logical fallacies, their history, and classifications.
Tips and strategies for recognizing flawed reasoning and common fallacies in LSAT Logical Reasoning questions.
A video tutorial that breaks down several common logical fallacies with clear examples.
While a book, the official PowerScore LSAT Logical Reasoning Bible has extensive sections on fallacies, often excerpted or discussed in their blog.
A practical overview of frequently encountered logical fallacies with relatable examples.
A blog post dedicated to dissecting logical fallacies relevant to the LSAT exam.
An extensive and well-organized database of logical fallacies with detailed explanations and examples.
An introductory video from Khan Academy explaining the concept of logical fallacies and providing examples.