Rank 4 by frequency | 402 questions in corpus (8.9% of all questions)
Weaken questions present an argument and ask which new fact, if true, would most undermine the conclusion. The correct answer does not need to destroy the argument — it just needs to reduce confidence in the conclusion more than any other choice. The correct answer always attacks the unstated assumption linking premises to conclusion, not the premises themselves.
Every Weaken stimulus contains an argument whose conclusion overreaches its premises in at least one way: a scope shift (conclusion uses a term or category not in the premises), a causal leap (premises show correlation; conclusion asserts causation), a degree/certainty escalation (premises support "possible"; conclusion states "certain"), a temporal mismatch (premises describe past; conclusion extends to future), or a comparison without basis (premises describe one situation; conclusion compares to another).
That overreach creates an unstated assumption linking premises to conclusion — the argument's vulnerability. Your task is to identify the answer that exploits that vulnerability: a NEW fact that damages the connection between premises and conclusion. The premises themselves are accepted as true and cannot be attacked; the conclusion's truth value is what is at issue. The answer does NOT need to disprove the conclusion — it only needs to make it LESS likely.
Correct Weaken answers cluster into a handful of recognizable strategies. Knowing them lets you anticipate what the right answer will look like.
Alternative explanation. The most common strategy on causal arguments. The premises show A is associated with B, and the conclusion asserts A caused B. An answer that identifies a different factor Z as the real cause damages the argument. This accounts for a large share of all Weaken correct answers.
Counterexample. A case where the premises hold but the conclusion fails — a specific instance that contradicts the generalization the argument rests on.
Attack an assumption. Directly challenge the unstated premise the argument depends on. Often this means showing that what the author quietly took for granted is not the case.
Undermine the data. Show the evidence is flawed, biased, or unrepresentative — the study had no control group, the sample was skewed, or the methodology was confounded.
Break an analogy. On comparison arguments, show a relevant difference between the compared items that makes the analogy fail.
Show the reasoning is flawed. Expose a timing mismatch (cause and effect don't align temporally), a scale or scope issue (numbers vs. percentages, part-to-whole error), or a reversed causation (Y actually causes X).
On causal stimuli specifically (roughly 30% of Weaken questions), there are five classic attack vectors: present an alternate cause, show a cause without effect (X occurred but Y did not), show an effect without cause (Y occurred but X did not), establish reversed causation, or expose a data/methodology problem. Recognizing a causal argument immediately narrows your search to this shortlist.
Variation 1 — Standard Weaken. "Which one of the following, if true, most seriously weakens the argument?" Single-speaker stimulus with a clear argument. Most common form.
Variation 2 — Weaken EXCEPT. "Each of the following, if true, weakens the argument EXCEPT:" Four answers weaken; one does NOT. Critical insight: the correct answer is NOT necessarily a strengthener — it is simply "not a weakener." It could be neutral, irrelevant, or even a strengthener. The logical opposite of "weaken" is "not weaken," not "strengthen."
Variation 3 — Dialogue/two-speaker format. "Which one of the following, if true, would provide [Speaker A] with the strongest counter to [Speaker B]'s response?" Must track two separate arguments and identify which to attack. Generally harder.
Variation 4 — Principle-based weaken. "Which one of the following principles, if valid, most seriously undermines the argument above?" The answer is an abstract principle whose application damages the argument.
Variation 5 — Weaken with causal stimulus. Roughly 30% of Weaken questions. Apply the five attack vectors above.
Variation 6 — Weaken with analogy/comparison stimulus. Attack vector: show a relevant difference between the compared items.
Step 1 — Read the stem first. Confirm it's a Weaken question before reading the stimulus with weakening in mind.
Step 2 — Read the stimulus for conclusion, premises, and gap.
Step 3 — Identify the conclusion using indicator words or by asking what the author is trying to prove.
Step 4 — Identify the premises. Separate evidence from background.
Step 5 — Articulate the gap. What does the author assume? Where does the logic leap?
Step 6 — Prephrase broadly. What TYPE of information would hurt this argument? For causal claims, think alternative explanation or reversed causation. For generalizations, think counterexample or unrepresentative sample.
Step 7 — Evaluate each answer. Accept as true; ask "does this make the conclusion less likely?"
Step 8 — Eliminate in order: irrelevant choices first, then strengtheners, then premise restaters.
Step 9 — Compare remaining candidates. Pick the one causing MORE damage with FEWER additional assumptions.
Step 10 — Adopt an "opposing counsel" mindset. Which answer represents the most devastating rebuttal?
The correct answer introduces new information not in the stimulus, targets an unstated assumption, and makes the conclusion less likely (without needing to disprove it). It often uses stronger wording (all, most, none) for decisive weakening, and crucially, it does NOT contradict stated premises — it attacks the inferential link, not the evidence itself.
Across most Weaken questions, correct answers fit one of these patterns: alternative explanation, undermined data, broken analogy, counterexample, timing mismatch, scale/scope issue, or reversed causation. Recognizing the argument's structure tells you which pattern to expect.
Trap 1 — Irrelevant/out of scope. Tangential topic that mentions stimulus terms but doesn't address the conclusion's logic.
Trap 2 — Opposite (strengthener). Makes the conclusion MORE likely — the direction-confusion trap.
Trap 3 — Premise restater. Repeats existing evidence; no net effect on the argument.
Trap 4 — Too extreme. Sweepingly absolute claim that goes beyond what's needed to damage the argument.
Trap 5 — Addresses the wrong conclusion. Weakens a claim that sounds like but isn't the actual conclusion — often a sub-conclusion or a misidentified main point.
Trap 6 — Requires extra assumptions. Could theoretically weaken, but only through a long chain of inferences you have to supply yourself.
Trap 7 — Attacks the premises. Tries to prove a stated premise false. Premises are accepted as true on the LSAT; the correct answer attacks the inferential link, not the evidence.
Trap 8 — Addresses background only. Relates to context surrounding the argument rather than the actual reasoning.
Buried or implicit conclusions not signaled by indicator words make the argument hard to pin down. Multiple possible weakeners where several choices genuinely weaken and only one attacks the CENTRAL assumption force you to compare damage levels. Abstract or unfamiliar topics — obscure scientific, legal, or philosophical content — strain your reading without changing the underlying task.
Subtle scope shifts — tiny but critical word changes, like "some" in the premises versus "most" in the conclusion — hide the gap in plain sight. Correct answers that seem tangential introduce a seemingly unrelated fact that devastatingly undermines the assumption once you trace the connection. Decoy strengtheners catch students who lose direction, and numbers/percentages traps exploit stimuli that conflate absolute numbers with rates.
The most common argument structures on this question type, roughly in frequency order: causal claims based on correlation (about 30%), prediction/recommendation based on evidence, generalization from sample, argument by analogy, rejection of alternatives ("the only explanation for X is Y"), numbers-vs-percentages confusion, comparison without basis, and conditional reasoning.
For practice, classic examples include PT47 S3 Q24 (Difficulty 3, alternative explanation) on a police commissioner crediting a mandatory sentencing law for a 15% violent crime decrease; PT64 S1 Q8 (Difficulty 3, counterexample) on the "bottom-up" ecosystem theory; and PT57 S2 Q14 (Difficulty 3, breaking a causal link) arguing that foraging leads to increased brain size in bees.
vs. Flaw. Both require identifying a weakness, but Weaken asks you to PROVIDE new information (a concrete fact); Flaw asks you to DESCRIBE the existing error (an abstract characterization). Weaken answers introduce facts; Flaw answers name reasoning errors.
vs. Necessary Assumption. The negation of a necessary assumption will weaken the argument — but Weaken answers are not limited to negated assumptions. They can introduce entirely new facts that attack the reasoning from outside.
vs. Strengthen. Mirror image. Identical structure, opposite direction. The most common strategy on both types is handling alternative explanations — introduce them on Weaken, eliminate them on Strengthen.
vs. Sufficient Assumption. Both introduce new information, but Sufficient Assumption answers GUARANTEE the conclusion while Weaken answers DAMAGE it. Opposite tasks built on the same gap structure.
Weaken stems include some form of weakens, undermines, calls into question, casts doubt, or counter, combined with "if true." Recognize them and immediately start hunting for the gap between premises and conclusion.