The 12 LSAT logical flaws, explained with examples
Flaw questions are the most common Logical Reasoning type. They all test the same skill: find the gap between the evidence and the conclusion. These twelve patterns cover nearly every gap the test uses.
How these differ from the fallacy pages. Our fallacy encyclopedia teaches the classic informal fallacies as general reasoning errors. These pages teach how each flaw appears inside LSAT Flaw questions: the argument shape, how the correct answer is usually worded, and the trap answers paired with it. Same family, test-day version.
All examples on these pages are original. None are real LSAT questions.
The causation flaw
Correlation is not causation, and the LSAT tests this constantly.
The sampling flaw
A bad sample proves nothing about the whole group.
Confusing necessary and sufficient conditions
Required for success is not the same as enough for success.
Circular reasoning
The conclusion is hiding inside the premises.
Equivocation: the word that changed meaning
One word, two meanings, one broken argument.
The part-to-whole flaw
What is true of the parts is not automatically true of the whole.
The false dilemma
It is rarely either/or.
Ad hominem on the LSAT
Attacking the arguer is not refuting the argument.
Absence of evidence is not evidence of absence
Not finding it does not mean it is not there.
The time-shift flaw
Old evidence, new conclusion.
Percentages vs. numbers
A bigger slice of a smaller pie can be less pie.
Survey and self-selection flaws
Who answers the survey decides what the survey says.
Which flaws cost you points?
The free diagnostic scores flaw questions by pattern, so you study the flaws you actually miss.