The Denial Test (also called the Negation Test) is a specific, mechanical technique for verifying assumption answers on the LSAT — and it's one of the few LR strategies that works almost like a formula, yet it's frequently mentioned in passing rather than taught as the systematic tool it actually is.
For any Necessary Assumption question, take an answer choice and negate it — make it false. If that negation destroys the argument's conclusion (makes the argument fall apart), the original answer choice was a necessary assumption. If negating it leaves the argument's logic intact, it wasn't necessary, no matter how relevant or true it sounds.
Suppose an argument concludes a new policy will reduce costs, assuming (among the answer choices) that “no alternative policy would reduce costs more.” Negate it: “some alternative policy WOULD reduce costs more.” Does that break the argument's conclusion? If the argument specifically claimed THIS policy is the best cost-reduction option, yes — confirming it's a necessary assumption.
Necessary Assumption questions are specifically about what the argument REQUIRES to be true, not what would merely help or strengthen it. Intuition tends to reward answer choices that feel supportive or relevant — but “supportive” and “necessary” are different bars, and only the Denial Test cleanly distinguishes them.
The Denial Test is built specifically for Necessary Assumption questions — applying it to Sufficient Assumption, Strengthen, or Weaken questions doesn't map cleanly, since those question types aren't testing what's logically required, just what's logically supportive. Using the wrong tool for the wrong question type is a common source of confusion for people who over-apply this technique.
On every Necessary Assumption question, negate your top 2 answer choices explicitly — out loud or on scratch paper — before locking in an answer. This adds a few seconds per question but eliminates an entire category of “feels right but isn't necessary” wrong answers.