LSAT Quiz: Necessary Assumption

What this quiz covers

This quiz focuses on Necessary Assumption, giving you a quick way to practice the rules, question types, and explanations that matter most for LSAT.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Voters who follow competitive campaigns care more about the volume of a candidate's advertising than they do about that candidate's stated policy positions.
2. Candidates who refuse corporate donations typically cannot raise enough funds from other sources to cover the extensive ad buys that competitive campaigns require. (correct answer)
3. Corporate donors who fund competitive campaigns generally expect specific policy concessions from candidates in exchange for the large sums they contribute.
4. The costs of the extensive ad buys that competitive campaigns require will continue to increase steadily across local media markets over time.
5. Accepting donations from corporate sources is the only method by which any candidate can reliably raise large sums of money quickly.

Explanation: The argument jumps from candidates who refuse corporate money raising 'less' money to their being unable to run competitively. That leap only holds if the money they can raise elsewhere still falls short of funding the ad buys competitive campaigns require. The correct answer states exactly this: non-corporate sources cannot cover the needed ads. Deny it, and the conclusion collapses, so the argument depends on it. The claim about voters caring more about ad volume than policy is irrelevant; the argument is about whether ads can be funded, not about how voters weigh ads against positions. The claim that corporate donors expect policy concessions concerns donors' motives, which the argument never needs. The claim that ad costs will keep rising over time adds a trend the argument does not rely on; the conclusion is about current competitiveness, not future costs. The claim that corporate donations are the 'only' way to raise large sums quickly is too strong; the argument needs only that other sources fall short of the required amount, not that no other fast method exists at all.

Question 2

1. The optical scanner reproduces every feature of a worn cylinder's grooves with perfect accuracy, whatever the age or condition of the cylinder in question may be.
2. The archive has already secured enough funding to complete the scanning of all of its wax cylinders within the next several years.
3. Playing a cylinder with a stylus captures features of a recording that optical scanning of the same cylinder's grooves cannot capture.
4. Wax cylinders kept in climate-controlled storage lose fidelity more slowly, over a given period, than cylinders kept at room temperature.
5. Studying the digital files produced by the scanner can serve the research purposes for which researchers have until now played the cylinders with a stylus. (correct answer)

Explanation: The conclusion is that after scanning, researchers can study the recordings' content without causing further fidelity loss in the cylinders. The premises establish only that a noncontact scanner exists and produces files; they never establish that the files serve research needs, which is the gap. Negating the credited response leaves researchers dependent on the stylus and the conclusion unsupported. Each distractor, when negated, leaves the inference intact: imperfect scanning accuracy, uncertain funding, stylus advantages that do not exist, and storage conditions all leave the director's reasoning standing.

Question 3

1. Every warbler population whose insect prey has advanced its emergence by nine days has advanced its own spring arrival by nine days as well.
2. The marsh warblers nesting at Kesler Pond feed on no insects other than those whose emergence has shifted earlier in recent decades.
3. The warblers' earlier arrival is not merely a separate effect of the same warmer springs that have made the insects emerge earlier. (correct answer)
4. The insects' earlier emergence at Kesler Pond is a response to the earlier spring arrival of the warblers that prey on them.
5. Marsh warblers that arrive at Kesler Pond earlier in spring raise more offspring, on average, than those arriving later.

Explanation: The conclusion is causal: the warblers arrive earlier in response to earlier insect emergence. The evidence is only that the two timings shifted by the same amount, so the argument depends on ruling out a common cause of both shifts. Negating the credited response installs that common cause and the conclusion fails. Negating the distractors does not: the inference survives if some other warbler populations have not tracked their prey, if these warblers also eat unshifted insects, if the insects' timing is not driven by the warblers, and if arrival date has no effect on breeding success.

Question 4

1. The solvent gel has removed nineteenth-century varnish without damaging the paint beneath in every previous restoration in which conservators have employed it.
2. The paint on the murals still on the walls does not respond to the solvent gel differently from the paint on the detached fragments. (correct answer)
3. No method available to the restorers other than the solvent gel would remove the yellowed varnish without damaging the paint.
4. Removing the yellowed varnish will return the murals' colors to something close to the appearance they had before 1890.
5. The paint on the Halverd murals is in the same condition today as it was in 1890, when the yellowed varnish was first applied.

Explanation: The conclusion is that applying the gel to the in-place murals will remove the varnish without damaging the paint; the only evidence is tests on detached fragments. The gap is the representativeness of those fragments. Negating the credited response severs the link between test and prediction, and the argument collapses. Negating each distractor leaves the argument standing: a past failure elsewhere does not undo these tests, the existence of a rival method is irrelevant, the visual outcome is beside the point, and the paint's 1890 condition does not matter since the fragments came from these same murals.

Question 5

1. All residents who named the length of the wait as their principal objection to the ferry would use it regularly if the average wait were eight minutes.
2. Residents who currently use the ferry object to the twenty-minute wait more strongly than do residents who never use it.
3. The second vessel will carry as many passengers on each trip as the vessel now serving the Riverport crossing carries.
4. The additional fares paid by new passengers will be sufficient to cover the cost of operating the second vessel.
5. Some residents who never use the ferry have no objection to using it other than the length of the wait. (correct answer)

Explanation:

1. Conclusion: the number of residents using the ferry will increase once the second vessel operates. The support is that the wait, cited by most non-users as their principal objection, will fall from twenty minutes to eight. The gap is between removing a principal objection and removing every objection that keeps a non-user away. 2. Negation test on the credited response: if no non-user's objections are exhausted by the wait, all of them still have a live reason to stay away, and the prediction is unsupported. The argument therefore needs at least some non-user for whom the wait is the whole objection. 3. Distractors: each is either stronger than needed or aimed elsewhere, and negating each leaves the prediction intact.

Question 6

1. The proposed composting facility would require no diesel fuel whatever to operate, since its machinery would run entirely on electricity.
2. Composting Halbrook's household organic waste locally would yield a soil amendment that gardeners in the town would be willing to purchase.
3. Reducing fuel consumption is the most important consideration for the council in deciding whether to approve the proposed composting facility.
4. Any reduction in the fuel Halbrook consumes in handling household organic waste would have to come from processing that waste somewhere within the town's limits.
5. Operating the proposed facility, including running its machinery, would not consume more fuel than trucking the waste to the landfill now consumes. (correct answer)

Explanation:

1. The conclusion is that building the facility would reduce Halbrook's fuel consumption for handling household organic waste; the gap is that the argument tallies only the fuel currently spent hauling and never accounts for the fuel the local alternative would require. 2. Negating the credited response makes the facility's operating fuel exceed the hauling fuel it replaces, so the net figure need not fall at all and the argument collapses. 3. The distractors survive negation: the facility may burn some diesel and still save fuel; salability of compost, the council's priorities, and the only-possible-source claim are all logically detachable from the fuel comparison.

Question 7

1. Greater locomotive acceleration reduces the average delay per trip on every rail route on which it is introduced.
2. Rail routes on which delays have been frequent are the routes to which a rail company is most likely to assign newly purchased electric locomotives.
3. The electric locomotives now used on the coastal route require less maintenance time between trips than the diesel locomotives they replaced.
4. No change on the coastal route during those twelve months other than the replacement of the locomotives contributed substantially to the reduction in delay. (correct answer)
5. Operating electric locomotives on the coastal route is less expensive for Ferris Rail than operating the diesel locomotives that they replaced was.

Explanation:

1. The conclusion is that greater acceleration produced the drop in average delay; the gap is the standard causal one—coincident change plus a plausible mechanism does not establish that this mechanism, rather than some other alteration on the route, produced the effect. 2. Negating the credited response installs a competing substantial cause and the attribution collapses. 3. Each distractor can be negated harmlessly: the universal claim is not needed for this one route; the assignment practice, maintenance intervals, and operating costs all leave the causal inference about this route's delays intact.

Question 8

1. Ferreira's translation of the Portuguese novel, which appeared from a small press, was among the translations eligible for last year's Hollis Prize. (correct answer)
2. Every translation that preserves the rhythm of its original closely reproduces that original's imagery less vividly than competing translations of the same work do.
3. The judges of the Hollis Prize compare the rhythm of candidate translations before considering how vividly each reproduces the original's imagery.
4. Marek's translation of the Portuguese novel is, on the whole, a better translation of that novel than Ferreira's translation is.
5. The rhythm of the Portuguese novel's original text can be reproduced fully in a translation into another language.

Explanation:

1. The conclusion is a comparison of Marek's and Ferreira's translations with respect to rhythm, drawn from Marek's having won a prize awarded within a defined pool; the gap is that the comparison holds only if Ferreira's translation belonged to that pool. 2. Negating the credited response removes Ferreira's translation from the pool the award ranks, and the award then licenses no claim about it. 3. The distractors survive negation: the imagery generalization, the judges' order of comparison, overall quality, and the possibility of fully reproducing rhythm all leave the award-based comparison intact.

Question 9

1. The clay from which the glazed vessels at Verrill were formed does not match any clay deposit lying within a day's walk of the site.
2. Every settlement that traded with Verrill during the period in question possessed kilns capable of firing clay well above 1,200 degrees Celsius.
3. Any kiln in the region that could fire clay above 1,200 degrees Celsius was fueled by something other than wood.
4. The residents of Verrill, who produced unglazed pottery of their own, valued glazed vessels highly enough to acquire them regularly from settlements in other parts of the region.
5. The glaze on the Verrill vessels could not have been produced at the site by any firing method that does not require a kiln. (correct answer)

Explanation:

1. Conclusion: the glazed vessels were manufactured elsewhere and traded to Verrill. The premises establish only that no kiln at Verrill could reach the required temperature; the gap is the unstated step from 'no adequate kiln' to 'no local production by any means.' 2. Negating the credited response supplies exactly the overlooked possibility — a non-kiln firing technique at Verrill reaching the needed temperature — and the inference to foreign manufacture collapses. 3. Each distractor can be negated without disturbing the inference, as detailed below.

Question 10

1. No lichen growing on the boulders beneath Craig Bern has been damaged by frost, falling debris, or grazing animals at any time.
2. Lichens of the same species growing on the cliff face above Craig Bern expand at about the same rate as those in the surrounding valley.
3. The lichens now growing on the Craig Bern boulders began growing on those surfaces only after the rockfall exposed them. (correct answer)
4. Any rock surface in the valley that has been exposed for 180 years bears at least one lichen 90 millimeters across.
5. The Craig Bern rockfall resulted from the same freeze-thaw processes that produce most rockfalls elsewhere in the surrounding valley.

Explanation:

1. Conclusion: the rockfall occurred roughly 180 years ago. The premises give a size and a growth rate; the gap is that a size-to-age calculation dates the exposure of the surface only if growth started with that exposure. 2. Negating the credited response permits pre-existing lichen on the rock, so the calculation no longer dates the rockfall and the conclusion collapses. 3. Each distractor survives negation, as explained below.

Question 11

1. Every cook now working in the Larkspur Inn's dining room kitchen, including its pastry cooks, has completed a training term with Dufort.
2. Any cook who has mastered Dufort's sauces, whatever else that cook may lack, completed a training term in Dufort's kitchen.
3. Voss's six years in Dufort's kitchen was a longer training term than most of Dufort's other cooks have completed.
4. The Larkspur Inn's dining room has been criticized for nothing other than the poor quality of the sauces it serves.
5. The sauces served in the Larkspur Inn's dining room will be prepared by Voss or by cooks working under her direction. (correct answer)

Explanation:

1. Conclusion: the criticism of the dining room's sauces will soon be obsolete. Premises: the new head cook trained with Dufort, and Dufort's trainees master her sauces. The gap is the missing link between one cook's skill and the sauces the dining room actually serves. 2. Negating the credited response severs that link and the conclusion no longer follows. 3. The distractors each fail the negation test, as set out below.

Question 12

1. Every cedar warbler that migrates through the region in September passes within sight of the ridge from which the observatory's counters work.
2. The region's cedar warbler population was larger in 1990 than it had been at any earlier point during the forty years of counting.
3. A shift in a bird species' migration route is generally the result of a decline in that species' population in the surrounding region.
4. Measures taken since 1990 to protect the vegetation on the ridge have succeeded in keeping the site attractive to migrating songbirds of several species.
5. Cedar warblers migrating through the region in September have not, since 1990, shifted onto routes that bypass the observatory's ridge. (correct answer)

Explanation: The conclusion is that the region's cedar warbler population has genuinely declined; the evidence is a halved count at a single fixed observation point, with effort and local vegetation held constant. The gap is the inference from 'fewer birds seen here' to 'fewer birds in the region,' which requires that the birds still pass this ridge. Negating (E) supplies exactly the competing explanation the argument needs to exclude: if the flyway moved, the count drop tells us nothing about population size, and the conclusion collapses. (A) is stronger than needed: even if not every warbler passes within sight of the ridge, a stable fraction passing it preserves the inference, so its negation leaves the argument standing. (B) concerns the population's history before 1990, which the conclusion does not address; negating it leaves the post-1990 comparison untouched. (C) inverts the relationship the argument must rule out, and negating it (route shifts are not generally caused by population declines) leaves the argument as it was. (D) supports the premise that the site remains suitable habitat rather than the conclusion about population; negating it leaves the stated premise about unchanged vegetation intact.

Question 13

1. No bottle sealed with a screw cap has ever been judged faulty by a consumer, whatever the wine inside it.
2. Consumers who detect cork taint in a bottle can distinguish it from other faults that wine may develop in the bottle.
3. Bottles of wine that consumers judge faulty are usually sealed with natural cork rather than with a screw cap.
4. Marchetti's customers do not prefer the appearance of a natural cork closure to that of a screw cap.
5. Sealing Marchetti's wine with screw caps will not produce other faults consumers detect in as large a proportion of bottles. (correct answer)

Explanation: The conclusion is that the proportion of Marchetti bottles consumers judge faulty will fall once screw caps replace cork; the premise is that screw caps never allow cork taint, which affected three percent of the winery's corked bottles. The gap is between removing one specific fault and lowering the overall fault rate. Negating (E) supplies an offsetting source of faults and the conclusion no longer follows. (A) would settle the matter but far exceeds what is needed: the argument survives if screw-capped bottles are occasionally faulty, so long as they are faulty less often than three percent. (B) concerns consumers' powers of discrimination, which do not affect the tally of bottles judged faulty; negating it leaves the argument standing. (C) states a converse-style generalization about faulty bottles the argument never requires. (D) addresses consumer preference about closures rather than the rate of faults concluded about.

Question 14

1. Every subscriber who did not reply to the questionnaire also prefers reading Corvid Quarterly in print rather than on a screen.
2. Most people who read Corvid Quarterly without subscribing to it prefer the print edition to reading the magazine on a screen.
3. Subscribers who prefer reading on a screen are more likely to answer a mailed questionnaire than those who prefer print.
4. Subscribers who replied to the questionnaire are not much more likely to prefer print than subscribers who did not reply. (correct answer)
5. Continuing to print Corvid Quarterly will not cost the publisher more than the print edition brings in from subscriptions.

Explanation: The conclusion is that most of the magazine's subscribers prefer the print edition; the evidence is that seventy percent of the roughly twenty percent who returned the questionnaire said so. The gap is response bias: the repliers must be reasonably representative of subscribers with respect to this preference. Negating (D) makes the repliers unrepresentative in exactly the relevant way and the generalization collapses. (A) would guarantee the conclusion but demands far more than representativeness requires. (B) concerns nonsubscribing readers, whom the conclusion excludes; negating it leaves the claim about subscribers intact. (C) posits a bias running the other way, which the argument does not need; negating it leaves the argument standing. (E) speaks to the financial wisdom of the printing plan rather than to the conclusion about preferences.

Question 15

1. The Quarterly's editors devoted at least as much time to evaluating each submitted manuscript last year as they did five years ago.
2. The Halden Quarterly is regarded by most mathematicians as more prestigious than the other journals to which manuscripts of comparable quality are commonly submitted.
3. Manuscripts submitted to the Quarterly last year were not, on the whole, of lower quality than those submitted five years ago. (correct answer)
4. The average quality of the manuscripts submitted to the Quarterly has risen substantially over the five years in question.
5. Readers of the Quarterly consider the articles it published last year more important than those it published five years ago.

Explanation: The conclusion is that the journal's standards for acceptance have risen; the evidence is that the acceptance rate fell from eighteen percent to nine percent while the number of manuscripts published stayed roughly the same. The gap is that the same rule applied to a much larger and weaker inflow of submissions would also halve the rate. (C) blocks that alternative explanation, and negating it destroys the inference. Negating the distractors leaves the argument standing: less time spent per manuscript (A) is compatible with stricter standards; the journal's prestige relative to other journals (B) is beside the point; a submission pool whose average quality merely held steady rather than rose (D) still yields the editors' conclusion; and readers' judgments of importance (E) concern the value of published work, not the acceptance threshold.

Question 16

1. Any hybrid orchid that has been registered with the society's archive and has bloomed at least twice may be entered in the society's annual exhibition.
2. Both of Aurelia's bloomings, in April and in July, occurred after its registration with the society's archive had been completed.
3. At the Bellamy exhibition, hybrids that have bloomed several times are judged more favorably than hybrids that have bloomed only twice.
4. Aurelia satisfies any requirement for entry, other than registration and two bloomings, that the society's rules may impose on hybrids. (correct answer)
5. Ferreira intends to enter Aurelia in this year's exhibition rather than to hold it back for a future exhibition.

Explanation: The conclusion is that Aurelia may be entered in this year's exhibition. The premises establish only that Aurelia meets the two conditions stated in the 'only if' rule, which are necessary conditions; nothing rules out further conditions. (D) supplies the needed guarantee that no unmet requirement remains, and its negation collapses the inference. Negating the distractors leaves the argument standing: even if not every registered, twice-bloomed hybrid is admissible (A), Aurelia may still be admissible; the rule as stated sets no order between registration and blooming, so a blooming preceding registration (B) is compatible with eligibility; how many-bloomed hybrids fare in judging (C) does not affect who may enter; and Ferreira's intentions (E) bear on whether the orchid will be entered, not on whether it may be.

Question 17

1. The five-toed pattern found in the Corrin prints is unique to Hadros among all herbivores known to have lived during the period.
2. No fossil bones have been recovered at the Corrin site that would allow the smaller prints to be matched with a particular skeleton.
3. Every member of a herbivore species, whether juvenile or adult, leaves footprints displaying the same number of toes.
4. Hadros traveled in herds that included juveniles as well as adults, as several other herbivores of the period are known to have done.
5. Apart from Hadros, no animal that was present at the Corrin site left footprints displaying a five-toed pattern. (correct answer)

Explanation: The conclusion is that the smaller Corrin prints were made by juvenile Hadros rather than by some other, smaller animal. The only evidence distinguishing these hypotheses is the shared five-toed pattern, so the argument depends on that pattern's being diagnostic among the animals that were actually at the site. (E) states precisely that, and negating it destroys the inference. Negating the distractors leaves the argument intact: another herbivore of the period possessing five toes (A) is harmless if it was not present at Corrin; the recovery of matchable bones (B) would if anything help; the failure of a general rule about uniform toe counts within species (C) does not undermine prints that are observed to share the pattern; and Hadros's not traveling in mixed herds (D) still allows juveniles to have walked those trackways at other times.

Question 18

1. The compost produced from the food waste Ferndale collects is of high enough quality to be used in the city's public parks and gardens.
2. Every household in Ferndale takes part in the curbside composting program and places all of the food waste it generates in the bins the city provides free of charge.
3. Households that generate relatively little food waste are more likely to take part in curbside composting collection than households that generate a great deal.
4. The food waste that households place in composting bins does not account for the entire decline in the weight of material Ferndale sends to its landfill. (correct answer)
5. The twelve percent decline in the weight of material sent to Ferndale's landfill will continue in each of the next several years.

Explanation:

1. Conclusion: Ferndale's households now generate less food waste than before the program. The support is a twelve percent drop in landfill tonnage. The gap is that a program that diverts food waste to compost lowers landfill tonnage without lowering the amount of food waste generated. 2. Negation test on the credited response: if the diverted food waste accounts for the whole decline, the decline is entirely a matter of where the waste goes, and the commissioner's inference collapses. So the argument requires that diversion not explain all of the decline. 3. Distractors: see distractor_reasons; negating each leaves the inference from the twelve percent decline to reduced generation exactly as strong or weak as it was.

Question 19

1. The gallery's windows are fitted with shutters that remain closed during the hours when watercolors are on display in the affected rooms.
2. The fifty-lux threshold at which fading begins applies to oil paintings as well as to the watercolors the gallery displays.
3. Any watercolor whose surface illumination exceeds fifty lux will fade noticeably within a year of being placed on display.
4. Light from sources other than the new lamps does not raise illumination at the watercolors' surfaces above fifty lux. (correct answer)
5. The new lamps reproduce the colors of the watercolors more accurately than the fixtures that the gallery removed did.

Explanation: The conclusion is that none of the displayed watercolors will fade from light exposure; the premise is that the new lamps deliver forty lux, below the fifty-lux fading threshold. The gap lies between one fixture's contribution and the total illumination reaching the surface. Negating (D) makes total illumination exceed the threshold and destroys the argument. (A) would secure the conclusion by eliminating daylight, but the argument survives its negation if the windows admit little light or the rooms have none. (B) extends the threshold to a medium the argument never discusses; negating it changes nothing about watercolors. (C) converts the stated necessary condition into a sufficient one with an added timeframe; negating it leaves 'fade only when above fifty lux' fully in force. (E) concerns color rendition rather than fading; negating it leaves the fading argument intact.

Question 20

1. Whenever a distinctive decorative motif appears at two sites that were occupied during the same century, the inhabitants of those sites traded with one another.
2. The spiral motif appears on pottery at Draymoor at least as frequently as it appears on pottery at the Kelvin site.
3. The spiral motif was not devised independently by potters at Kelvin and by potters at Draymoor, however similar the clay available to each. (correct answer)
4. The inhabitants of Kelvin traded more extensively with Draymoor than with any settlement lying closer to Kelvin than Draymoor does.
5. Pottery was among the goods most frequently carried over long distances during the century in which Kelvin and Draymoor were occupied.

Explanation:

1. The conclusion is that the inhabitants of Kelvin and Draymoor traded with one another, inferred solely from a motif shared by contemporaneous sites; the gap is that a shared motif is evidence of contact only if it was not invented twice over. 2. Negating the credited response makes independent invention the explanation of the shared motif, which removes the argument's only evidential link between the two populations. 3. The distractors leave the argument standing when negated: the universal rule is stronger than needed, and relative frequency, comparative trading partners, and the general prominence of pottery in long-distance trade are all detachable from the inference.