LSAT Flaw Questions Overview

Flaw Questions in Logical Reasoning

Identifying Flaw Questions

  • Look for specific language in the question stem:
    • "Describes a flaw"
    • "Questionable technique"
    • "Vulnerable to criticism"
    • "Takes for granted" (indicates an assumption flaw)
    • "Fails to consider" (suggests a weakening flaw)

Approach to Flaw Questions

  • The approach to flaw questions is identical to other questions in the assumption family (sufficient assumption, necessary assumption, strengthening, and weakening questions).
  • Process:
    • Identify the conclusion.
    • Find the evidence supporting the conclusion.
    • Evaluate if the conclusion logically follows from the evidence (it should not).
    • Identify the gap in reasoning.
    • Evaluate the argument.

Evaluating Arguments

  • Look for reasoning structures:
    • Comparison
    • Causation
    • Conditional logic
  • Identify the missing piece in the argument.
  • Anticipate the answer.
  • Use knowledge of trap answer patterns to eliminate incorrect choices.

Common Reasoning Structures in Flaw Questions

Comparative Reasoning (71% of flaw questions)

  • Example: Striking vs. Not Striking
    • Some union members want to strike.
    • The union member argues against striking due to financial losses (cuts into strike fund, steep fine, major financial loss).
    • Flaw: Incomplete comparison.
      • Fails to consider the financial implications of not striking.
      • Lacks a full picture of both outcomes to make a sound comparison.
    • Fails to consider information that would help us figure out the relative merit of the two choices, that it's failed to include information that would be relevant to the decision.
    • Incorrect Answer Examples:
      • Fails to consider a strike might cause financial loss even without a fine (strengthens the argument).
      • Fails to define "major financial loss" (definition flaw not present).
      • Takes for granted the most important factor is financial strength (too strong of an assumption).
      • Fails to establish a better opportunity to strike later (irrelevant relationship).
    • Correct Answer Example:
      • Fails to consider the benefits to be gained from a strike might outweigh the costs (weakens the argument).

Causation

  • Example: Sports Car vs. Minivan
    • Friends claim driving recklessly in a sports car will lead to an accident.
    • Research shows minivans have lower accident rates than sports cars (correlation).
    • Conclusion: Trading a sports car for a minivan will lower the risk of an accident (causation).
    • Flaw: Mistakes correlation for causation.
    • The argument suggests that a minivan would cause a lower accident rate, moving from a correlation to a causal relationship.
    • Incorrect Answer Examples:
      • Relies on a sample that is too narrow (wrong flaw).
      • Misinterprets evidence that a result is likely as evidence that the result is certain (likely vs. certain flaw not present).
      • Mistakes conditions sufficient for bringing about a result for a condition necessary for doing so (conditional logic flaw not present).
      • Relies on a source that is probably not well informed (appeal to authority flaw not present).
    • Correct Answer Example:
      • Infers a cause from a mere correlation

Conditional Logic (23% of flaw questions)

  • Example: Anthropologist's Claim
    • Anthropologist's claim: If the human species had not evolved the ability to cope with diverse natural environments, then the species could not have survived prehistoric times.
      • ¬Cope \implies ¬Survive
    • Conclusion: The anthropologist's claim is false.
    • Evidence: Australopithecus afarensis thrived in diverse environments but became extinct.
      • Cope \land ¬Survive
    • Flaw: Mistakes a sufficient condition for a necessary condition.
    • The argument attempts to refute the claim.
      • Refuting a conditional requires meeting the sufficient condition and denying the necessary condition.
      • The argument actually refutes the reversal of the anthropologist's claim rather than the claim itself.
    • The contrapositive of the anthropologist's claim is: Survive \implies Cope
    • To refute this, one would need to show: Survive \land ¬Cope
      • The evidence shows: Cope \land ¬Survive
    • Incorrect Answer Examples:
      • Takes for granted that if one species had a characteristic that it happened to enable to survive certain conditions, at least one related extinct species must have had the same characteristic (irrelevant relationship, gets terms wrong, reverses the argument).
      • Generalizes from the fact that one species with a certain characteristic survived certain conditions that all related species with the same characteristic must have survived exactly the same conditions (generalization flaw not present).
      • Fails to consider the possibility that Australopithecus afarensis had one or more characteristic that lessened its chances of surviving prehistoric times (strengthens the argument instead of weakening it).
      • Fails to consider the possibility that even if a condition caused a result to occur in one case, it was not a necessary cause for the result to occur in a similar case (irrelevant relationship, gets the terms wrong.).
    • Correct Answer Example:
      • It confuses the conditions being required for a given result to occur in one case with a condition being sufficient for such a result to occur in a similar case.

Trap Answer Patterns

  • Scope:
    • Out of scope answer choices are easiest to eliminate.
    • Answer choices that correctly describe a flaw but not one in the argument are tempting but wrong.
    • Answer choices that correctly describe something that happened but is not a flaw are also wrong.
  • Logic:
    • Answer choices that strengthen the argument (do the opposite) are wrong.
    • When an answer choice begins with "takes for granted that," be wary of ideas stronger than what was assumed.
    • Irrelevant relationships are wrong because of logic.
  • Degree:
    • Answer choices can be too strong (presenting more than what was assumed).
    • Answer choices can be too weak (not forcefully undermining the argument).

Summary

  • Spot Flaw Questions: Look for flaw, vulnerable to criticism, questionable technique, or fallacious reasoning in the question stem.
  • Keep an eye out for these phrases in the question stems "Takes for granted", and "Fails to consider".
  • Reasoning Structures: Pay attention to comparison, causation, and conditional logic.
  • Trap Answers:
    • Correctly describes a flaw, but not in the argument.
    • Out of scope.
    • Too strong (for assumptions).
    • Too weak (for weakening).
    • Correctly describes something that happened, but it isn't a flaw.
    • Irrelevant relationships.