Critical Thinking flaw taxonomy
Accept the reasons as true. Your job is to test whether they prove the conclusion.
Map it first
- Conclusion: what should you accept?
- Reasons: what supports it?
- Bridge: what unstated claim links them?
Six flaws
| Flaw | Quick test |
|---|---|
| Cause from association | Could it run backwards, or a third factor explain both? |
| Selection bias | Who chose to be in the sample? |
| Necessary treated as sufficient | What else must be true? |
| False choice | Is there a third option? |
| Weak analogy | Is the feature that matters actually shared? |
| Slippery slope | Which link has no support? |
Find the missing comparison
Worked example Optional seminars and higher scores
After a college introduced optional morning reasoning seminars, attendees scored higher on a TARA practice test than non-attendees. So the seminars caused the improvement, and all applicants should attend. What is the main flaw?
- Some applicants may not apply to university.
- Seminar attendees may already have been stronger or more motivated.
- A practice test contains Critical Thinking and Problem Solving.
- Morning sessions may be inconvenient for commuters.
- The college cannot require students at other colleges to attend.
Why this works: The second option gives a rival explanation. The students chose themselves.
Why the tempting route fails: Inconvenience matters for the policy, not for the reasoning.
How the wrong answers are built
- True but irrelevant to the reasoning.
- Attacks the topic, not the argument.
- Strengthens when the stem asks for a flaw.