LSAT Strengthen and Weaken questions: moving the needle, not settling it

Strengthen and Weaken are the same question pointed in opposite directions. Both hand you an argument with a gap between its evidence and its conclusion. Strengthen asks which new fact narrows that gap. Weaken asks which widens it. Neither asks you to establish anything.

That last point costs people more time than any other feature of the type. The credited answer does not have to disprove the conclusion, and on Weaken it usually does not come close. It only has to make the conclusion less well supported than it was a moment ago. Students hunting for a knockout blow read past the answer that merely lands.

Find the gap first, always

Written for this page: a clinic reports that patients who attended its new nutrition workshop had lower cholesterol six months later than patients who did not attend, so the clinic concludes the workshop lowers cholesterol.

The gap is not hidden. Attendance was voluntary, so the two groups may differ in ways that have nothing to do with the workshop — people who sign up for a nutrition workshop are plausibly already more inclined to change what they eat. Any answer that makes those groups look more alike strengthens. Any answer that makes them look more different weakens.

Notice how much work that one sentence did. Once you can state the gap, you are no longer evaluating five sentences on their general persuasiveness — you are asking one question of each: does this make the two groups more comparable, or less? Four answers will not touch that question at all.

The three moves that weaken almost anything causal

• Offer an alternative cause — something else explains the outcome. The single most common credited answer on causal Weaken questions.
• Reverse the direction — the supposed effect came first, or produced the supposed cause.
• Break the correlation — a case where the cause is present and the effect is not, or the reverse.

Strengthen runs the same three in reverse: rule out the alternative, fix the direction, show the pattern holds where it should. If you recognize an argument as causal — and a great many of them are — you can predict the shape of the answer before you read one.

Why the boldest answer is usually a trap

Wrong answers on Strengthen questions frequently sound more decisive than the right one. They make a sweeping claim about the topic that would be excellent news for the author if true, but do not connect to the specific leap the argument made. Meanwhile the credited answer is a modest sentence closing exactly the gap you identified.

This is not a trick, it is the type working as designed. The question asks which answer most strengthens the argument — this argument, with this gap. An answer that is impressive about the subject matter and silent about the gap strengthens nothing at all.

One further trap worth naming: an answer that supports the conclusion directly rather than supporting the reasoning. If the conclusion is that the workshop lowers cholesterol, an answer asserting that nutrition education generally lowers cholesterol restates the conclusion in wider terms without helping this argument get there. The test uses this shape often, because it feels like support.