Strip the argument to its skeleton
Replace the actual nouns with placeholders (A, B, C) and rewrite the argument as a bare logical form: conditional structure, quantifier used ('all,' 'some,' 'no'), and the specific move from premises to conclusion.
Two arguments about completely different topics can share an identical skeleton, and two arguments about the same topic can have completely different skeletons: topic overlap is never the test.
For parallel flaw specifically
First identify the exact error in the original: affirming the consequent, denying the antecedent, treating a necessary condition as sufficient, an unrepresentative sample. Then find the answer choice committing that exact same error, not just any error.
A choice with a valid argument, or a choice with a real but different flaw, is always available as a trap. Match the specific mistake, not just the presence of a mistake.
What LSAC says about comparing patterns of reasoning
LSAC lists recognizing similarities and differences between patterns of reasoning among the skills the Logical Reasoning section tests, which is the skill a parallel reasoning question isolates. LSAC also says these questions do not require specialized logical terminology, so you can describe a structure in your own words.
LSAC says taking practice tests under time limits helps you estimate how much time you can afford on each question and identify the question types that need more practice. Timing yourself on parallel questions in particular shows how much of a 35-minute section they take.
3 original practice questions
Written for this guide, not taken from any licensed test. Your result is saved on this device only.
If the bridge is closed, then traffic will be rerouted through downtown. Traffic has been rerouted through downtown. Therefore, the bridge must be closed. Which of the following arguments has a flawed pattern of reasoning most similar to the argument above?
Answer and explanations
Correct answer: B. The original affirms the consequent: A leads to B, B is true, so it concludes A: ignoring other possible causes of B. Choice B mirrors this exactly. A is valid modus ponens, D commits a different flaw (denying the antecedent), and E is valid modus tollens.
Every member of the orchestra can read sheet music. Diego can read sheet music. Therefore, Diego is a member of the orchestra. Which of the following exhibits a flawed pattern of reasoning most similar to that in the argument above?
Answer and explanations
Correct answer: A. The original treats a trait guaranteed by membership as though it guarantees membership. Choice A repeats that exact structure. B is valid, C and D are valid (modus tollens), and E starts from a weaker 'some' premise, a different structure entirely.
A watch that is running loses accuracy the longer it goes without being wound. This watch has not been wound in three weeks. Therefore, this watch is running very inaccurately. Which of the following contains reasoning most similar to that in the argument above?
Answer and explanations
Correct answer: A. Both arguments state a degree relationship (more time without X means more of effect Y) then plug in a specific time value to conclude a specific degree of the effect. Choice A tracks this exactly; D reverses the inference (effect to cause), a different and invalid structure.
Questions this guide answers
What is an LSAT parallel reasoning question?
It asks for the answer choice built from the same abstract logical structure as the original argument, regardless of topic.
What is a parallel flaw question?
A parallel reasoning question with one more requirement: the matching argument must also commit the same specific error as the original.
How do I find the structure of an argument?
Replace the nouns with placeholders such as A, B and C and rewrite it as a bare form showing the conditional structure, the quantifiers and the move to the conclusion.
Do I have to match the quantifiers in a parallel question?
Yes, exactly. All, some and no are different claims, so a choice using some when the original used all is not parallel.
Does topic overlap help on parallel questions?
No. Two arguments on different topics can share an identical skeleton, and two arguments on the same topic can have completely different ones.
Which errors show up in parallel flaw questions?
Affirming the consequent, denying the antecedent, treating a necessary condition as sufficient, and an unrepresentative sample are examples. Name the exact error, then find that same one.
Why are parallel flaw questions full of traps?
A choice with a valid argument, or one with a real but different flaw, is always available. Match the specific mistake, not just the presence of a mistake.
How does LSAC suggest using timed practice?
LSAC says practice tests under time limits help you estimate the time you can spend per question and show which question types need more work.
Your next steps
- Rewrite the original argument in abstract A/B/C form before reading the choices.
- Match quantifiers ('all' vs. 'some' vs. 'no') exactly, not approximately.
- On parallel flaw questions, name the specific error first, then hunt for that same error.
- Eliminate any choice that is logically valid when the original argument was flawed.