The logical fallacies the LSAT actually tests

Most published fallacy lists are philosophy-department lists. They are long, they are full of Latin, and perhaps a third of what is on them ever appears on the LSAT. This is the shorter list — the errors the test reuses, with the phrasing the answer choices actually use for each, because recognizing the phrasing is half the work.

Every example here was written for this page. Reading a fallacy defined is nearly useless; reading it committed is what makes it recognizable later.

Errors about cause

• Correlation to cause — "Neighborhoods with more libraries have higher literacy, so building libraries raises literacy." Perhaps literate populations lobby for libraries. Answer phrasing: presumes that because two things are correlated, one causes the other.
• Reversed causation — the same pairing, with the direction backwards. Answer phrasing: mistakes an effect for a cause.
• Overlooked alternative — one explanation is offered and treated as the only one available. Answer phrasing: fails to consider that some other factor may account for the result.
• Post hoc — B followed A, therefore A caused B. Answer phrasing: infers a causal relation from the mere temporal sequence of two events.

Errors about evidence and groups

• Unrepresentative sample — "Ninety per cent of respondents to our website poll support the change." People who answer a website poll are not people. Answer phrasing: draws a general conclusion from a sample that is unlikely to be representative.
• Absence of evidence — "No study has found harm, so it is safe." Answer phrasing: treats the lack of evidence for a claim as evidence against it.
• Percentage against number — a hospital's mortality rate rising while it treats far more patients tells you very little on its own. Answer phrasing: confuses a proportion with an absolute quantity.
• Missing comparison — "Our graduates earn eighty thousand, so the program works." Compared to whom? Answer phrasing: offers a figure without the baseline needed to interpret it.

Errors about the structure of the claim

• Necessary treated as sufficient — "You need a permit to build, and she has one, so she may build." A permit is required, not enough. Answer phrasing: treats a condition necessary for an outcome as though it were sufficient.
• Part and whole — "Every player on the team is excellent, so the team is excellent." Answer phrasing: assumes what is true of the parts must be true of the whole.
• Equivocation — "The law should treat all men equally; he is not much of a man." Answer phrasing: relies on a term being used in two different senses.
• Circularity — "The policy is fair because it treats people as they deserve, and people deserve what a fair policy gives them." Answer phrasing: assumes what it sets out to establish.
• False dilemma — "Either we cut the budget or the program closes." Answer phrasing: presents two alternatives as exhaustive when others are available.
• Possibility to certainty — "It could be the cause, so it is the cause." Answer phrasing: treats something that may be true as though it had been established.

Errors about the arguer

• Attacking the source — the speaker's funding, motive, or inconsistency is offered instead of an answer to what they said. Answer phrasing: rejects a claim on the basis of its source rather than its merits.
• Appeal to authority or popularity — believed by experts, or by many, therefore true. Answer phrasing: takes the acceptance of a claim as evidence of its truth.
• Straw man — the opposing view is restated in a weaker form and then defeated. Answer phrasing: misrepresents a position in order to dismiss it.

One caution about lists like this. The credited answer on a Flaw question describes the error the argument in front of you committed — not the most famous error, and not one that resembles it. Four of the five choices routinely name real fallacies that are simply absent from that passage. Knowing the list makes them recognizable; it does not excuse you from checking which one is actually there.