LSAT Cannot Be True questions: the answer the passage rules out

A Cannot Be True question asks which answer is impossible if everything in the passage is true. Stems read "if the statements above are true, which one of the following CANNOT be true" — and sometimes appear as "must be false", which is the same demand in different words.

This is an Inference question with the polarity flipped. On Inference you look for the one answer that must be true; here you look for the one that cannot. The other four are not false — they are simply not ruled out, which is a much weaker property than being supported.

Impossible, not implausible

The bar is contradiction. An answer that seems unlikely, or that the author would probably disagree with, or that no reasonable person would expect, is still perfectly possible unless the passage rules it out. Students who pick on the basis of "that doesn't sound right" get these wrong consistently.

The credited answer conflicts with something the passage states, or with something that follows necessarily from what it states. Everything else — every plausible-sounding, on-topic, sensible-seeming choice — survives.

Where the contradiction usually hides

• A conditional. If the passage says every member of a group has a property, an answer describing a member without it cannot be true. These are the most common and the most mechanical.
• A stated maximum or minimum. "No more than a third" makes any answer requiring more than a third impossible.
• An exclusive pair. If two categories are said not to overlap, an answer placing something in both is dead.
• A definitional claim. The passage defines a term, and an answer uses it in a way the definition forbids.
• Arithmetic. Percentages and totals that cannot both hold — often the quietest contradiction on the page.

The habit

Work the conditionals before touching the answers. Write the contrapositive of anything with "only", "unless", "all" or "no" in it. Most credited answers on this type violate a contrapositive, and the contrapositive is the half students skip.

Then, for each choice, ask a single question: could this be true at the same time as everything in the passage? Four times the answer is yes, and you move on quickly. Do not argue with the four — they do not have to be likely, only possible.