Use negation for necessity, a proof for sufficiency and opposite outcomes for evaluation.
GMAT45 min study guide9 indexed sections
BY THE END, YOU CAN
Explain and apply necessary-assumption negation test
Explain and apply sufficient-support reasoning
Explain and apply evaluate with opposite outcomes
Explain and apply distinguish assumption from inference
Explain and apply missing links
Explain and apply feasibility and alternative explanations
Explain and apply scope and modal precision
BEFORE YOU START
Read an argument or passage without assuming that every speaker agrees.
Distinguish a claim from the evidence offered for it; interpret simple counts and percentages.
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LEARN THROUGH ORIGINAL PRACTICE
Original GMAT-style worked examples and practice
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01 / UNDERSTAND & APPLY
Three question types, three different tests
A necessary-assumption question asks what the argument depends on. A sufficient-support question asks what, added to the premises, makes the conclusion follow. An evaluation question asks which information would help judge the argument. These tasks can use similar-looking options but demand different tests.
First isolate the exact conclusion and the stated grounds. A claim about net savings needs a financial bridge; a claim about fewer car trips needs substitution, not merely interest in a shuttle. Write the missing relation in plain language before reading choices.
02 / UNDERSTAND & APPLY
Necessary assumptions and the negation test
Negate a candidate precisely and add the negation to the argument. If this destroys a required bridge, the candidate is necessary. If the reasoning can still stand, the candidate may merely help or may be irrelevant. The test assesses dependence, not whether the candidate sounds plausible.
Negate “all” as “not all,” “some” as “none,” and “at least one” as “none.” Negate “more than 10” as “10 or fewer.” Do not turn a modest claim into an exaggerated opposite. “Not every customer leaves” is not the same as “no customer leaves.”
ORIGINAL WORKED EXAMPLE
Apply the test to a cost argument
A firm will replace its current process with a machine. The machine’s annual operating cost is $40,000; the old process costs $60,000 annually. The manager concludes that the replacement will save money in its first year after including all costs. Is it necessary that additional first-year replacement costs be less than $20,000?
The stated annual operating-cost difference is $20,000.
For positive first-year net savings, additional replacement costs must be below that difference, assuming the stated operating figures cover the respective annual operations.
Negation: additional replacement costs are $20,000 or more. Then net savings are zero or negative, defeating the exact positive-savings conclusion.
Answer Yes. “Less than $20,000” is necessary under the stated cost accounting; zero additional costs is not necessary.
03 / UNDERSTAND & APPLY
Negate the proposition, not your emotional reaction
A necessary assumption can be weak. To conclude that at least one applicant will qualify when certification is required, it may be necessary that not all applicants lack certification. Negating that means every applicant lacks it.
For empirical arguments the negation test should target the proposed reasoning. An argument may have several possible independent routes to its conclusion; a statement necessary for one route is not automatically necessary for every conceivable way the conclusion could be true. Ask whether the stated argument requires it.
ORIGINAL WORKED EXAMPLE
Negate a quantified claim
Negate “Some scheduled deliveries will arrive before noon.”
Some means at least one.
Its negation says zero scheduled deliveries will arrive before noon.
“Some will arrive after noon” is not the negation, because early and late deliveries can coexist; delivery exactly at noon also matters to the boundary.
Answer No scheduled deliveries will arrive before noon.
04 / UNDERSTAND & APPLY
Sufficient support closes every relevant gap
To test sufficiency, combine the option with the premises and derive the conclusion. A statement may be much stronger than necessary yet still be a correct sufficient condition. Conversely, a necessary condition can leave a major gap and fail to guarantee the conclusion.
Use the exact logical direction. If all eligible proposals are reviewed, showing a proposal was reviewed does not establish eligibility. A sufficient bridge might instead say every reviewed proposal is eligible, but that is an additional rule rather than a fact already implied.
ORIGINAL WORKED EXAMPLE
Complete a deductive bridge
Every proposal that meets both the budget rule and the safety rule is eligible. Proposal K meets the budget rule. Which added statement is sufficient to prove K eligible? A: Some eligible proposals are expensive. B: K meets the safety rule. C: K was submitted early. D: Eligible proposals are reviewed. E: K has a short title.
The rule requires budget AND safety. Budget is given; B supplies the missing conjunct.
A, C and E do not address the requirements. D points from eligibility to review, not from any given fact to eligibility.
Answer B
05 / UNDERSTAND & APPLY
Evaluate with two possible answers
A good evaluation question produces materially different assessments when answered in opposite ways. Try a yes answer and a no answer, or a high value and a low value. Explain how each affects the same conclusion. If both answers leave the argument similarly supported, the question is unlikely to be central.
The most useful unknown often concerns substitution, transfer, comparative cost, baseline conditions or alternative causes. Do not choose a question merely because it concerns the same broad topic. A question about a shuttle’s paint color is about shuttles but may say nothing about reduced car traffic.
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These are alternative answers to the same evaluation question, not successive events. Neither answer alone settles every possible effect of the plan.
ORIGINAL WORKED EXAMPLE
Use the two-outcome test
A town proposes a free shuttle to reduce car trips to its center. Surveys show many residents would ride it. Which is more useful to determine: whether riders would replace car trips, or whether they prefer green seats?
If riders replace car trips, shuttle use supports the traffic goal.
If riders mostly replace walking or add trips, high ridership gives much less support for reduced car trips.
Seat-color preferences do not provide the same direct contrast for the stated goal.
Answer Whether riders would replace car trips.
06 / UNDERSTAND & APPLY
An assumption is an input; an inference is an output
An inference follows from information already supplied. An assumption is an unstated input needed to move from supplied information to a conclusion. The two can share subject matter but occupy different logical positions.
Suppose the text says every installed sensor passed inspection, and concludes the new system will operate reliably. “The installed sensors passed inspection” is a premise or direct inference from the universal statement; “passing inspection predicts reliable operation under actual conditions” is a possible missing bridge. Do not label a repeated premise an unstated assumption.
ORIGINAL WORKED EXAMPLE
Classify the bridge
A courier predicts a new route will be faster because a trial drive took less time. Is “trial conditions are relevant to normal delivery conditions” an inference from the trial result or an assumption behind the prediction?
A single short trial time does not establish normal traffic, stops or parcel-handling conditions.
The prediction relies on the trial being informative about the actual operating setting.
Answer It is an assumption about transfer, not an inference guaranteed by the trial result.
07 / UNDERSTAND & APPLY
Feasibility, alternatives and modal precision
Plans need means as well as desires. A plan to extend clinic hours requires staffing at those times; popularity alone does not establish capacity. A causal argument needs evidence against plausible alternatives, not merely an assumption that alternatives are impossible.
Preserve modal strength. “Can reduce costs” requires a possible feasible route; “will reduce costs next year” predicts an actual outcome; “must reduce costs” is stronger still. A necessary-assumption answer should not demand perfect certainty when the conclusion is only a limited possibility.
08 / UNDERSTAND & APPLY
Practice: choose the correct test
Specify whether you are testing necessity, sufficiency or evaluative relevance.
ORIGINAL PRACTICE · 1
1. Negate “All returning participants improved.”
Reveal answer & reasoning
At least one returning participant did not improve.
“None improved” is stronger than the negation. The correct negation needs only one counterexample within the stated group.
ORIGINAL PRACTICE · 2
2. Negate “The total cost is at most $500.”
Reveal answer & reasoning
The total cost is more than $500.
“At most” includes equality. Its negation excludes $500 and every smaller value.
ORIGINAL PRACTICE · 3
3. A project saves $9,000 in annual labor but costs $3,000 in annual maintenance. Its one-time installation cost is $8,000. Does it save money in year one, using only these costs?
Reveal answer & reasoning
No; year-one net savings are −$2,000.
$9,000−$3,000−$8,000=−$2,000. Annual recurring savings do not imply first-year savings after installation.
ORIGINAL PRACTICE · 4
4. All approved requests require a signature. Request M is signed. Is that sufficient to establish approval?
Reveal answer & reasoning
No.
Approval → signature. Signature alone does not imply approval; other conditions may remain unmet.
ORIGINAL PRACTICE · 5
5. Every package with both tags R and S receives priority handling. Package N has R. What added fact is sufficient?
Reveal answer & reasoning
N has S.
The conjunction R and S activates the given rule. This is sufficient under the rule, even though there might be other unstated ways to obtain priority handling.
ORIGINAL PRACTICE · 6
6. A retailer credits new displays for a sales increase. Why is it useful to ask whether prices also fell at the same time?
Reveal answer & reasoning
The answers change the availability of a competing explanation.
If prices fell substantially, price may explain some increase; if prices did not change, that specific alternative is reduced. Neither answer alone settles all causal uncertainty.
09 / UNDERSTAND & APPLY
Practice: do not demand more than the conclusion
Use exact scope and the appropriate diagnostic.
ORIGINAL PRACTICE · 1
7. A plan needs at least one qualified operator. Must it assume every employee is qualified?
Reveal answer & reasoning
No; that is stronger than necessary.
The plan can work with one qualified operator even if others are not qualified. Negating “every employee is qualified” leaves that possibility intact.
ORIGINAL PRACTICE · 2
8. A shuttle argument concludes it will reduce car trips. Which question is most useful? A: Will most riders substitute for car trips they otherwise would make? B: Is the shuttle’s name short? C: Do residents like the logo? D: Is the timetable printed in blue? E: Was the proposal presented on a Tuesday?
Reveal answer & reasoning
A
Opposite answers directly change support for the car-trip mechanism. B through E lack a stated connection to substitution; they are topical background rather than central evaluation evidence.
KEEP THE BIG IDEAS
Quick revision
Negation tests necessity; a derivation tests sufficiency.
Evaluation asks for information whose opposite outcomes matter to the same claim.
Preserve quantifier and modal boundaries instead of inventing extreme opposites.
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