Parallel Flaw Questions – LSAT Logical Reasoning

Identifying a Parallel-Flaw Question

• Look for trigger language in the stem:
  • “exhibits flawed reasoning most similar to …”
  • “the flawed pattern of reasoning … most closely resembles …”
  • “the questionable pattern of reasoning … most similar to …”
• “Flawed reasoning” + “most similar / most closely resembles / parallels” ⇒ a Parallel Flaw task.
• Only ≈4 % of LR items; 1–3 per exam.

Standard Five-Step Approach

1. Find the conclusion
2. Find the evidence supporting it
3. Evaluate the reasoning
   • Is it valid or flawed?
   • What structure is being used (conditional, comparison, causal, etc.)?
4. Anticipate what a matching answer must look like (both structure and flaw)
5. Use trap-answer patterns to eliminate remaining choices

Structures That Appear Most Often

• $55\%$ Conditional logic (if/then, sufficient ↔︎ necessary)
• $43\%$ Comparative reasoning (opposite ends of a spectrum, “more/less”, “none/all”)
• $10\%$ Causal reasoning (cause → effect)
• Comparative plays a bigger role in Parallel-Flaw than in regular Parallel questions.

Example 1 – “Moderate Barkers” (Comparative)

• Stimulus facts
  • All Labradors bark a great deal.
  • All Saint Bernards bark infrequently.
  • Rose’s dogs are Lab × Saint Bernard mixes.
• Conclusion: Rose’s dogs are moderate barkers (mid-point assumption).
• Embedded flaw: Assumes blending extremes necessarily yields a mid-point.

Working the Answer Choices

• A. Students that study diligently ⟶ good grades; some non-diligent ⟶ good grades; Jane studies “somewhat” diligently ⟶ “somewhat” good grades.
  • Same outcome for both groups ⇢ Wrong premise & no spectrum.
• B. Type-A chemical = extremely toxic; Type-B = non-toxic; cleaner is A + B ⟶ moderately toxic.
  • Mirrors “blend extremes ⇢ middle.” Correct.
• C. Hanson School → Greene County, Edwards School → Wynn County; Perry family attends both → some in Greene, some in Wynn.
  • Valid deduction, no flaw ⇢ Wrong validity.
• D. Transcriptionists know shorthand, Engineers know calculus; Bob is both → knows both.
  • Also valid ⇢ Wrong validity.
• E. Kenisha’s dresses well-made, Connie’s badly-made; half closet well-made, half badly-made → half Kenisha’s, half Connie’s.
  • Flaw = mistaking necessary for sufficient, different from spectrum-blend flaw ⇢ Wrong flaw.

Example 2 – Conditional Logic & Reversal

• Rule: If someone is a paleomycologist (PM) ⇒ acquainted with all PM publications.
• Fact: Prof. Mansour is acquainted with Prof. D’Angelis’ publications (D’Angelis is a PM).
• Conclusion: Mansour must be a PM.
• Flaw: Reverses necessary ↔︎ sufficient (ACQ → PM instead of PM → ACQ).

Evaluating Answer Choices

• A. Original flight delayed ⇒ connecting flight delayed. Frida’s connecting delayed ⇒ original delayed.
  • Perfect reversal. Correct.
• B. If agent misses shift ⇒ others work harder. No one missed ⇒ others didn’t work harder.
  • Negating sufficient ⇢ negating necessary (Denying the antecedent). Wrong flaw (negation, not reversal).
• C. Fuel price ↓ ⇒ expenses ↓ & income steady. Fuel ↓ several times ⇒ GA made a profit.
  • Conclusion unrelated to rule ⇢ Wrong conclusion.
• D. ≥1 year at GA ⇒ can join retirement. Gavin 3 yrs ⇒ does participate.
  • Treats “can” as “does”. Conclusion too strong / wrong flaw.
• E. Competitor fares ↓ ⇒ GA must match or lose passengers. GA carried more passengers last year ⇒ GA matched fares.
  • Adds hidden premise “competitors reduced fares.” Resulting chain is valid ⇢ Wrong validity.

Trap-Answer Statistics & Patterns

(Percentages sum >100 because many wrong choices fail on multiple grounds)

• $42\%$ Wrong conclusion (content, strength, or scope)
• $33\%$ Wrong premise / mismatched evidence
• $33\%$ Wrong validity (valid vs. flawed)
• $33\%$ Wrong flaw (different logical error)
• $8\%$ Different reasoning type (conditional vs. comparative vs. causal)

Common Logical Missteps to Match / Avoid

• Reversal: claiming $B\to A$ from a rule $A\to B$
• Negation: from $A\to B$ + $\lnot A$ infer $\lnot B$
• Spectrum mash-up: assuming “middle” result from mixing extremes
• Necessary ↔︎ Sufficient confusion overall
• Treating “can / may” as “will / does” (over-strengthening conclusions)

Practical Tips for Timed Work

• Spend extra seconds diagnosing stimulus flaw; saves minutes in choices.
• Skip reading entire wrong answer once a mismatch appears (premise scope, validity, etc.).
• Keep a mini-checklist in head:
  1. Same overall structure?
  2. Same number/type of premises?
  3. Same conclusion form & strength?
  4. Same flaw?

Ethical / Real-World Echoes

• Important to recognize why an argument is bad, not just that it is, to avoid replicating such reasoning in professional/legal writing.
• Comparative “middle-ground” fallacy mirrors everyday assumptions (e.g., thinking half caffeine + half decaf ⇒ medium caffeine impact).

Numeric / Statistical References Recap

• $4\%$ of LR ≈ Parallel Flaw items per test.
• Distribution of reasoning types: $55\%$ conditional, $43\%$ comparative, $10\%$ causal.
• Wrong-answer frequencies: $42\%$ wrong conclusion, $33\%$ wrong premise, $33\%$ wrong validity, $33\%$ wrong flaw, $8\%$ wrong reasoning type.

Key Takeaways

• Identify the flaw precisely; every evaluation step hinges on that clarity.
• Check both structure and validity—a valid answer can never parallel a flawed stimulus.
• Most traps hide in the conclusion; scrutinize wording, scope, modality (must / can / probably).
• Use percentages above to guide your elimination strategy: conclusion first, premises next, then validity/flaw.
• Practice conditional translations (sufficient ↔︎ necessary) and comparative extremes to gain speed.