Weaken

71 questions

All types71 Multiple choice36 Multiple select17 True / False18

Agronomist: In a multi-year agricultural study across several commercial grain farms, fields planted with hairy vetch as a winter cover crop produced subsequent corn yields that were on average 20 percent higher than those from fields left fallow during the winter. Because hairy vetch is known to fix atmospheric nitrogen into the soil, this substantial increase in yield must be directly attributable to the additional nitrogen provided by the cover crop.

Which of the following statements, if true, most seriously weaken the agronomist's argument? Select all that apply.

Select all that apply

Fields planted with hairy vetch retained significantly higher soil moisture throughout early summer droughts than fallow fields, and moisture retention is the primary determinant of corn yields in these regions.

Soil samples taken from the vetch-planted fields immediately before corn planting showed nitrate concentrations nearly double those of the fallow fields.

Farmers participating in the study applied identical high levels of synthetic nitrogen fertilizer to all fields, raising soil nitrogen well above the maximum threshold usable by corn plants.

The commercial farms in the study did not actually achieve any measurable increase in corn yield following the winter cover crop trials.

Several other leguminous cover crops fix atmospheric nitrogen at substantially higher rates per acre than hairy vetch.

Show answer & explanation

Answer: Fields planted with hairy vetch retained significantly higher soil moisture throughout early summer droughts than fallow fields, and moisture retention is the primary determinant of corn yields in these regions.; Farmers participating in the study applied identical high levels of synthetic nitrogen fertilizer to all fields, raising soil nitrogen well above the maximum threshold usable by corn plants.

Answer

The argument is weakened by the statement establishing soil moisture retention as an alternate cause for the higher yields, as well as the statement demonstrating that preexisting synthetic fertilizer levels already saturated the crops' nitrogen requirements.

The correct statements undermine the argument by challenging the causal attribution: one introduces an alternative causal factor (enhanced moisture retention during critical drought periods) that fully accounts for the yield disparity, while the other shows that nitrogen levels were already saturated beyond the threshold of utility, eliminating the possibility that supplemental nitrogen caused the yield improvement.

Step-by-Step Solution

Identify the conclusion and the supporting premises in the stimulus

Premise: Fields with hairy vetch cover crops produced 20 percent higher corn yields than fallow fields. Premise: Hairy vetch fixes atmospheric nitrogen. Conclusion: The yield increase must be directly attributable to the additional nitrogen.

Isolating the structural components reveals the core causal claim made by the author.

Identify the underlying assumptions and potential points of vulnerability

The author assumes that nitrogen fixation is the only relevant difference caused by the cover crop and that additional nitrogen was capable of driving yield gains in this setting.

Causal arguments can be weakened by offering an alternative cause for the effect or showing that the proposed cause could not have produced the effect.

Evaluate each option to find all statements that undermine the causal connection

Introducing moisture retention as the decisive factor provides an alternative explanation, while showing that nitrogen was already supplied past the crop's uptake capacity negates the proposed causal mechanism.

Both findings directly attack the link between the cover crop's nitrogen fixation and the observed yield increase.

Key Concept

Weakening causal arguments through alternative explanations and demonstrating the ineffectiveness of the proposed cause

Estimated Time:1m 30s

Question 2Question →

Chronobiologist: A recent two-year study monitored adolescent students who completed their academic assignments during early morning hours rather than late evening hours. These morning-studying students reported substantially higher sleep quality and improved memory retention. Therefore, shifting mentally demanding tasks from late evening to early morning directly optimizes sleep architecture and cognitive performance in adolescents.

Which of the following statements, if true, most seriously weaken the chronobiologist's argument? (Select all that apply)

Select all that apply

Students who voluntarily shifted their study schedule to the morning already adhered to stricter household limits on evening screen exposure, an independent factor known to improve adolescent sleep quality.

Completing intellectually intensive assignments late at night causes sustained elevations in pre-sleep physiological arousal that inhibit restorative slow-wave sleep.

Adolescents with naturally advanced circadian rhythms, who inherently experience superior sleep consolidation and baseline memory retention, are disproportionately more likely to adopt morning study routines.

A portion of the self-reported sleep logs kept by students during the study contained minor recording discrepancies regarding exact bedtimes.

Adult professionals in demanding occupations do not experience measurable improvements in cognitive performance when shifting work hours from evening to morning.

Show answer & explanation

Answer: Students who voluntarily shifted their study schedule to the morning already adhered to stricter household limits on evening screen exposure, an independent factor known to improve adolescent sleep quality.; Adolescents with naturally advanced circadian rhythms, who inherently experience superior sleep consolidation and baseline memory retention, are disproportionately more likely to adopt morning study routines.

Answer

The statements establishing an alternative confounding cause (household screen time limits) and a self-selection bias based on preexisting biological chronotypes both weaken the argument by undermining the author's direct causal conclusion.

The conclusion asserts a direct causal relationship based purely on a correlation observed between study timing and sleep/memory metrics. The statement showing that morning studiers were subject to stricter evening screen time limits provides an alternative causal explanation for the improved sleep. Similarly, the statement showing that students with naturally advanced circadian rhythms already possess superior sleep consolidation demonstrates that baseline biological differences, rather than the schedule change itself, likely account for the observed benefits.

Step-by-Step Solution

Identify the conclusion and underlying premises in the argument.

Premise: Morning-studying adolescents had better sleep quality and memory scores than evening studiers. Conclusion: Shifting mentally demanding tasks to the morning directly causes optimized sleep architecture and cognitive retention.

Weaken questions require targeting the unstated logical gap between the correlation observed in the premise and the causal link asserted in the conclusion.

Formulate potential vulnerabilities in the causal inference.

The author assumes no confounding third variables (such as other lifestyle habits) and no self-selection bias (inherent physiological differences between morning and evening types) explain the observed correlation.

Causal claims based on observational studies are inherently vulnerable to alternate causes, reverse causality, and selection bias.

Evaluate each choice against the causal gap.

The option citing stricter household screen limits introduces a plausible confounding variable, and the option noting inherent circadian advantages explains the correlation via selection bias. Both undermine the conclusion.

Introducing credible alternative explanations directly breaks the necessary assumption that the homework timing itself caused the beneficial outcomes.

Key Concept

Alternative Causal Explanations and Selection Bias

Estimated Time:1m 30s

Question 3Question →

City officials have introduced a municipal subsidy for independent bookstores, contingent on the stores hosting free weekly community events. Critics argue the subsidy will financially harm these businesses, as the grant amount is significantly smaller than the staffing costs required to host such events. However, this concern is unfounded. A recent comprehensive survey revealed that independent bookstores that already host regular community events report 40 percent higher annual revenues than those that do not. Thus, participating in this subsidy program will ultimately improve the financial health of the bookstores.

Which of the following, if true, most seriously weakens the argument?

The free community events hosted by independent bookstores frequently attract large crowds of new customers who make substantial retail purchases during the event.

The monetary value of the new municipal subsidy is too small to cover even half of the expected operational costs for the weekly events.

Independent bookstores that currently host regular community events generally do so because their exceptionally high pre-existing revenues allow them to afford the associated costs.

Many independent bookstores have recently shifted a significant portion of their sales online in order to compete with larger corporate retailers.

Only those independent bookstores that host community events are capable of remaining financially viable in the current economic climate.

Show answer & explanation

Answer: Independent bookstores that currently host regular community events generally do so because their exceptionally high pre-existing revenues allow them to afford the associated costs.

Answer

The option stating that independent bookstores hosting events do so because their high pre-existing revenues allow them to afford the costs.

The argument assumes that because independent bookstores hosting events have higher revenues, the events must be the cause of that financial success. The correct answer undermines this causal assumption by indicating reverse causality: these bookstores host events *because* they already possess high revenues. If this is true, the survey data is plagued by selection bias. Consequently, forcing a financially struggling bookstore to host events in order to receive a small subsidy will merely impose additional costs without producing the promised revenue boost, severely weakening the author's conclusion.

Step-by-Step Solution

Analyze the argument's structure.

Premise: Stores that currently host events have 40% higher revenues. Conclusion: Participating in the event-based subsidy program will improve a bookstore's financial health.

Identifying the core premises and the main conclusion is necessary to pinpoint the logical gap in the reasoning.

Identify the underlying assumption.

The author assumes a causal relationship: hosting community events causes the higher revenue. The author rules out alternative explanations for the survey data.

Weaken questions often hinge on exposing flawed causal assumptions or selection bias in the evidence.

Evaluate the options for a counter-explanation.

The correct option demonstrates reverse causality (selection bias). It shows that the bookstores in the survey already had high revenues, meaning the events are a luxury afforded by success, not the cause of it.

If the cause and effect are reversed, then forcing financially struggling stores to host events will merely impose additional costs without generating the promised revenue, directly undermining the conclusion.

Key Concept

Weaken

Question 4Question →

Archaeologist: A recently translated archive of clay tablets from the ancient city of Kesh details all raw metal shipments received over a decade. The proportion of raw tin to copper recorded in these logs is significantly lower than the high proportion of tin found in the ornate bronze artifacts excavated from the city's contemporaneous elite tombs. This discrepancy indicates that the bronze items buried with the elite were likely imported as finished luxury goods rather than locally smelted from Kesh's raw material shipments.

Which one of the following, if true, most seriously weakens the archaeologist's argument?

Raw tin was extraordinarily expensive and was exclusively reserved by Kesh artisans for smelting the specialized items destined for the elite class, whereas copper was used abundantly for common tools.

Trace element analysis of the ornate bronze artifacts reveals distinct isotopic signatures that match copper ores found hundreds of miles away from Kesh.

The translation of the clay tablets is highly contested among scholars, with some arguing that the symbol for tin has been misinterpreted.

The bronze artifacts found in the elite tombs of Kesh are significantly larger and heavier than the standard bronze tools used by commoners during that period.

The overall volume of copper imported into Kesh vastly exceeded the volume of tin imported during the decade recorded in the archive.

Show answer & explanation

Answer: Raw tin was extraordinarily expensive and was exclusively reserved by Kesh artisans for smelting the specialized items destined for the elite class, whereas copper was used abundantly for common tools.

Answer

The statement regarding tin being exclusively reserved for elite items while copper was used broadly for common tools.

The argument relies on a flawed statistical assumption: that the composition of a specific subset of goods (elite tomb artifacts) must perfectly match the aggregate composition of all raw materials entering the city. The correct answer destroys this assumption by showing that distribution was heavily skewed. If artisans used the abundant copper for everyday tools but reserved the rare, expensive tin almost entirely for elite items, then local artisans could easily produce high-tin bronze for the elite. This perfectly bridges the gap between the low-tin trade records and the high-tin artifacts, proving that local smelting is a viable explanation and weakening the conclusion that the items had to be imported.

Step-by-Step Solution

Identify the main conclusion of the argument.

The bronze items buried with the elite were imported as finished goods rather than locally smelted.

This is the author's main claim based on the discrepancy presented in the premises.

Identify the premises supporting the conclusion.

The proportion of tin to copper in raw shipments (overall imports) is significantly lower than the proportion of tin found in the elite bronze artifacts.

The author uses this mismatch in proportions as the sole evidence for the conclusion.

Identify the unstated assumption linking the premise to the conclusion.

The argument assumes that any bronze smelted locally in Kesh would necessarily reflect the aggregate tin-to-copper ratio of the city's total raw metal shipments.

For the premise to prove the conclusion, the overall average of raw materials must dictate the composition of all individual local products.

Find the option that attacks this assumption.

The correct answer shows that the aggregate ratio does not dictate the specific ratio of elite goods, because tin was disproportionately concentrated into items made for the elite.

If local artisans concentrated the limited tin into a few elite items, the elite items would have a high tin ratio despite the city's overall low tin imports, destroying the author's logic.

Key Concept

Identifying Flaws in Generalization / Part-to-Whole Fallacy

Question 5Question →

Environmental Engineer: To mitigate the urban heat island effect, city planners propose resurfacing municipal roads with a newly developed reflective polymer sealant. In trials on an open, isolated test track, asphalt coated with the sealant absorbed 60 percent less solar energy and maintained surface temperatures 8 degrees Celsius lower than untreated asphalt. Therefore, applying this sealant across the city's roadways will substantially reduce daytime ambient air temperatures in adjacent residential neighborhoods.

Which of the following, if true, most seriously weakens the environmental engineer's argument?

The reflective polymer sealant is substantially more expensive to produce and apply than the conventional sealants currently used on municipal roads.

The specialized thermal sensors used during the test track trials failed to measure the temperature of the asphalt at regular hourly intervals.

In dense residential neighborhoods, solar radiation reflected by street surfaces is primarily absorbed by the vertical walls of adjacent buildings rather than escaping into the upper atmosphere.

The reflective sealant also inhibits asphalt from retaining heat overnight, significantly lowering evening ambient temperatures in nearby parks.

Unless every single roadway in the metropolitan region is coated with the sealant, no neighborhood will experience any measurable reduction in daytime heat.

Show answer & explanation

Answer: In dense residential neighborhoods, solar radiation reflected by street surfaces is primarily absorbed by the vertical walls of adjacent buildings rather than escaping into the upper atmosphere.

Answer

In dense residential neighborhoods, solar radiation reflected by street surfaces is primarily absorbed by the vertical walls of adjacent buildings rather than escaping into the upper atmosphere.

The conclusion relies on the assumption that lower surface temperatures on pavement will translate directly into cooler ambient air in residential areas. If reflected solar energy is captured and absorbed by the surrounding buildings, the thermal energy remains trapped within the neighborhood environment, preventing the predicted drop in ambient air temperature.

Step-by-Step Solution

Analyze the argument's structure and identify premises and conclusion.

Premise: Reflective sealant reduced surface heat by 8°C on an open test track. Conclusion: Applying the sealant across municipal roads will reduce ambient air temperatures in adjacent residential neighborhoods.

Weaken questions require identifying the inferential gap between experimental evidence and real-world application.

Identify the unstated assumption linking the premises to the conclusion.

The argument assumes that reducing pavement absorption on an open track will result in net atmospheric cooling in dense residential settings without redirecting thermal energy into surrounding structures.

Highlighting discrepancies between test conditions and actual urban environments exposes the logical vulnerability.

Evaluate choices for an alternative mechanism or factor that breaks this connection.

Showing that reflected solar radiation is absorbed by nearby building walls demonstrates that the heat remains in the neighborhood air layer, neutralizing the expected cooling effect.

Introducing a factor that undermines the causal outcome directly weakens the conclusion.

Key Concept

Evaluating causal arguments by identifying unrepresented differences between test environments and applied settings

Estimated Time:1m 15s

Question 6Question →

Paleontologist: Fossil specimens of *Eoconstrictor*, an ancient snake from the Eocene epoch, exhibit cranial and vertebral adaptations characteristic of modern arboreal snakes that hunt in high forest canopies. Additionally, fossilized stomach contents from three distinct specimens contain remains of an arboreal lizard species. Therefore, *Eoconstrictor* must have hunted primarily in tree canopies rather than foraging along the forest floor.

Which of the following statements, if true, undermine the paleontologist's argument? Select all that apply.

Select all that apply

The arboreal lizard species identified in the gut contents spent substantial periods basking on the forest floor, where it was most easily ambushed.

Modern snakes sharing the cranial and vertebral adaptations of *Eoconstrictor* capture more than ninety percent of their prey in tree canopies.

Biomechanical models indicate that the bone density and mass of *Eoconstrictor* would have prevented it from climbing or navigating slender canopy branches.

Fossilized stomach contents from predatory reptiles of the Eocene epoch are rarely preserved well enough to identify prey species reliably.

Other predatory reptiles living in the same Eocene ecosystem preyed upon ground-dwelling rodents rather than arboreal lizards.

Show answer & explanation

Answer: The arboreal lizard species identified in the gut contents spent substantial periods basking on the forest floor, where it was most easily ambushed.; Biomechanical models indicate that the bone density and mass of *Eoconstrictor* would have prevented it from climbing or navigating slender canopy branches.

Answer

The statements showing that the prey was accessible on the forest floor and that the predator had physical constraints preventing canopy climbing both undermine the conclusion.

The argument concludes that the predator hunted primarily in tree canopies based on two premises: anatomical similarity to modern arboreal snakes and the presence of arboreal lizard remains in its stomach. The statements that weaken this reasoning show that the arboreal lizard prey was accessible on the forest floor during basking and that the predator possessed physical traits that made climbing into canopies biomechanically unfeasible.

Step-by-Step Solution

Identify the argument's premises and main conclusion

Premises: The snake exhibits skeletal traits seen in canopy hunters, and its stomach contents contained an arboreal lizard. Conclusion: The snake hunted primarily in tree canopies rather than on the forest floor.

Clarifying the conclusion and supporting evidence reveals the core assumption: that anatomical similarity and prey identity necessarily imply canopy foraging behavior.

Identify potential vulnerabilities and alternative explanations

The argument assumes that arboreal prey could only be caught in trees and that morphological traits definitively indicate canopy locomotion.

Weakeners will either offer an alternative explanation for how canopy prey was consumed on the ground or demonstrate why canopy hunting was improbable.

Evaluate each choice to identify all statements that weaken the reasoning

The choice showing that the lizards basked on the ground severs the link between prey type and canopy hunting, while the choice showing biomechanical climbing limitations directly counters the feasibility of canopy hunting.

Both statements independently introduce evidence that diminishes the plausibility of the paleontologist's conclusion.

Key Concept

Identifying alternative explanations and physical constraints to weaken causal and behavioral inferences

Question 7Question →

Economist: A recent three-year study compared manufacturing firms that adopted automated inventory management software with firms that retained manual tracking systems. The automated firms experienced a 30 percent greater reduction in unscheduled assembly line shutdowns. The study's authors concluded that implementing automated inventory management directly causes reductions in assembly line shutdowns by preventing component shortages caused by manual record-keeping errors.

Which of the following, if true, most seriously weakens the study's conclusion?

The initial capital expense required to purchase and integrate automated inventory software exceeded the revenue recovered from reducing shutdown frequency.

A post-implementation audit revealed that component shortages caused by manual record-keeping errors were virtually nonexistent among the firms that converted to automation.

The firms that invested in the automated software had concurrently overhauled their aging production machinery as part of a broader facility modernization initiative.

Most automated inventory software systems require periodic software updates and cannot completely eliminate every conceivable type of clerical error.

The automated firms did not actually experience a 30 percent reduction in assembly line shutdowns over the three-year period.

Show answer & explanation

Answer: The firms that invested in the automated software had concurrently overhauled their aging production machinery as part of a broader facility modernization initiative.

Answer

The statement indicating that the firms investing in automated software simultaneously overhauled their production machinery as part of a broader modernization program.

The argument concludes that automated software was the direct cause of the decrease in shutdowns. The correct answer undermines this by introducing a confounding variable: these same firms modernized their mechanical equipment at the same time. This alternative factor provides an independent, plausible reason why line shutdowns decreased, thereby casting substantial doubt on the claim that the software was responsible.

Step-by-Step Solution

Identify the main conclusion and underlying evidence in the stimulus.

Evidence: Automated inventory firms had a 30 percent greater reduction in shutdowns than manual tracking firms. Conclusion: Automated software directly caused this reduction by eliminating manual record-keeping errors.

Deconstructing the argument isolates the causal claim from the empirical correlation.

Identify the reasoning gap in the causal claim.

The author assumes that no other confounding variable or alternative cause distinguishes the automated firms from the manual firms during the study period.

Causal conclusions based on observational group comparisons are vulnerable to unaddressed third variables.

Evaluate the answer choices to identify the option that supplies an alternative cause.

The choice showing that automated firms also overhauled aging production machinery accounts for the reduced shutdowns through improved mechanical reliability rather than inventory logging.

Providing a confounding factor directly undermines the validity of attributing the outcome exclusively to the software.

Key Concept

Alternative Explanations in Causal Arguments

Estimated Time:1m 15s

Question 8Question →

Civil Engineer: To reduce groundwater seepage that was degrading structural foundations in the historic district of Oakhaven, the municipal water authority installed permeable pavement across all surrounding pedestrian plazas two years ago. Since the installation, average basement water ingress reports from property owners have declined by over 60 percent. Given that annual rainfall levels remained consistent with historical averages during both years, the permeable pavement installation was responsible for the decline in water ingress.

Which of the following, if true, most seriously weakens the civil engineer's argument?

Pedestrian plazas in neighboring districts that did not install permeable pavement experienced no reduction in basement water ingress reports over the same two-year period.

Annual precipitation in Oakhaven was unevenly distributed across several individual months during the two-year period, despite the total yearly volume matching historical averages.

Shortly before the permeable pavement was laid, the municipal water authority completed extensive repairs that sealed several chronically leaking water mains beneath the historic district.

Permeable pavement has never been shown to completely eliminate groundwater accumulation beneath building foundations in any urban environment.

The municipal expenditure required to install and maintain permeable pavement far exceeded the district's initial budgetary projections.

Show answer & explanation

Answer: Shortly before the permeable pavement was laid, the municipal water authority completed extensive repairs that sealed several chronically leaking water mains beneath the historic district.

Answer

The statement showing that extensive repairs sealed chronically leaking subterranean water mains beneath the historic district just prior to the pavement installation most seriously weakens the argument.

The correct response introduces an alternative explanation for the observed reduction in basement flooding. If subterranean water mains beneath the historic district were leaking heavily and were sealed immediately before the pavement was laid, the repair of those mains—rather than the permeable pavement—could fully account for the 60 percent decline in basement water ingress.

Step-by-Step Solution

Isolate the argument's premises and main conclusion.

Premises: Permeable pavement was installed two years ago; basement water ingress reports fell by over 60 percent; annual rainfall remained at historical averages. Conclusion: The permeable pavement installation caused the decline in water ingress.

Deconstructing the argument reveals the underlying causal claim linking the installation to the outcome.

Identify the primary logical vulnerability or unstated assumption.

The author assumes that no other concurrent event or intervention was the true cause of the reduced subterranean moisture.

Causal arguments on the LSAT are vulnerable to alternate causes that explain the observed correlation.

Evaluate the choices for a plausible alternative explanation.

Sealing heavily leaking underground water mains right before the pavement was installed provides a strong competing explanation for the reduction in groundwater ingress.

Demonstrating an alternate source of subterranean water was eliminated severs the causal attribution to the pavement.

Key Concept

Alternative Causal Explanations in Logical Reasoning

Estimated Time:1m 45s

Question 9Question →

Public Health Researcher: A recent observational study monitored municipal road-resurfacing crews routinely exposed to concentrated asphalt vapor and found that they exhibited significantly higher concentrations of systemic inflammatory biomarkers than municipal administrative workers. Because both cohorts demonstrated comparable baseline sleep patterns, nutritional profiles, and self-reported psychological stress, the researchers concluded that prolonged inhalation of asphalt vapor directly triggers this systemic inflammatory response.

Which of the following, if true, most seriously weakens the public health researchers' argument?

Controlled laboratory trials on mammalian lung tissue demonstrated that exposure to aerosolized asphalt compounds induces an immediate, dose-dependent release of inflammatory biomarkers.

Detailed physiological assessments revealed that municipal administrative workers had substantially lower baseline psychological stress and significantly better sleep quality than the study reported.

The road-resurfacing crews regularly operated heavy pneumatic tampers and vibratory compactors, tools whose prolonged mechanical vibration is independently known to trigger elevated systemic inflammatory biomarkers.

All airborne volatile compounds encountered in heavy industrial construction projects inevitably produce severe systemic inflammation in every exposed individual.

Municipal administrative workers who were occasionally exposed to minor vehicle exhaust fumes in office parking structures showed no detectable elevation in systemic inflammatory markers.

Show answer & explanation

Answer: The road-resurfacing crews regularly operated heavy pneumatic tampers and vibratory compactors, tools whose prolonged mechanical vibration is independently known to trigger elevated systemic inflammatory biomarkers.

Answer

The finding that road-resurfacing crews regularly operate pneumatic tools whose mechanical vibration independently triggers systemic inflammation most seriously weakens the argument.

The correct choice introduces an alternative explanation for the elevated inflammatory biomarkers observed among road-resurfacing workers. The author's argument relies on a causal inference: because road crews had higher biomarkers than office workers with similar sleep, diet, and psychological stress, asphalt vapor must be the cause. Demonstrating that road crews were simultaneously exposed to another distinct condition—mechanical vibration from heavy pneumatic equipment—that independently induces systemic inflammation undermines the conclusion that asphalt vapor is the causal agent.

Step-by-Step Solution

Identify the conclusion and supporting premises of the argument.

Premises: Road crews exposed to asphalt vapor have higher inflammatory biomarkers than office workers with similar sleep, diet, and psychological stress. Conclusion: Asphalt vapor inhalation directly triggers this systemic inflammatory response.

Isolating the core premises and conclusion clarifies the causal claim.

Determine the logical gap and implicit assumption.

The author assumes that because sleep, nutrition, and psychological stress were controlled, no other confounding factor unique to road crews could account for their elevated inflammatory biomarkers.

Causal arguments on the LSAT frequently overlook alternative causes for an observed correlation.

Evaluate the options to identify new information that provides a plausible alternative cause or exposes the unstated assumption.

The option establishing that road crews operate vibrating pneumatic machinery—a known independent cause of systemic inflammation—provides an alternative explanation for the elevated biomarkers, breaking the direct causal link to vapor inhalation.

Providing an unconsidered alternative cause for the effect directly undermines a causal conclusion.

Key Concept

Weakening Causal Arguments via Alternative Explanations

Estimated Time:2m 0s

Question 10Question →

Organizational Psychologist: A study tracked twenty mid-sized technology firms that replaced assigned private cubicles with unassigned, open-plan workstations. Over the subsequent two years, documented collaborations between employees from different functional departments increased by thirty percent. The researchers concluded that eliminating assigned seating directly increased interdepartmental collaboration by encouraging spontaneous daily interactions among employees who otherwise would not meet.

Which of the following, if true, most seriously weakens the organizational psychologist's argument?

Prior to the workstation transition, employees in these firms spent the vast majority of their working hours interacting solely with colleagues seated immediately adjacent to them.

Employees at technology firms that maintain assigned seating generally report higher overall job satisfaction than employees who share unassigned desks.

The firms transitioned to unassigned workstations as part of a broader corporate restructuring that mandated cross-departmental project teams for all major product initiatives.

The tracking methods used during the two-year study failed to record several informal, undocumented conversations that occurred in hallway areas.

No employee in any open-plan work environment can ever maintain sustained concentration on complex individual assignments.

Show answer & explanation

Answer: The firms transitioned to unassigned workstations as part of a broader corporate restructuring that mandated cross-departmental project teams for all major product initiatives.

Answer

The statement showing that the firms adopted unassigned workstations concurrently with a corporate restructuring that mandated cross-departmental teams directly undermines the conclusion by introducing an alternative cause.

The correct response introduces an alternative explanation for the thirty percent increase in cross-departmental collaborations. If the firms simultaneously enacted a restructuring that explicitly mandated interdepartmental project teams, this corporate requirement—rather than spontaneous daily interactions enabled by open-plan seating—is likely responsible for the documented increase. This severs the inferred causal connection between the physical seating layout and the collaborative outcome.

Step-by-Step Solution

Analyze the argument's structure and identify the conclusion and premises.

Premise: Moving to unassigned workstations correlated with a 30% increase in interdepartmental collaborations. Conclusion: The seating change directly caused the increase via spontaneous interactions.

Weaken questions require identifying the exact causal gap between the evidence (correlation) and the author's claim (causation).

Identify the primary flaw or underlying assumption in the author's reasoning.

The author assumes that no other concurrent policy or confounding factor was responsible for the increase in cross-departmental collaborations.

Causal conclusions are vulnerable to alternative explanations, reverse causation, or third-variable confounders.

Evaluate the answer choices to find the one that introduces an effective alternative cause.

The finding that the workstation change was part of a company-wide restructuring requiring joint project teams provides a direct alternative explanation for the rise in collaborations.

Demonstrating that an institutional mandate occurred simultaneously undermines the claim that seating-induced spontaneous interactions were the cause.

Key Concept

Causal reasoning and alternative explanations in Logical Reasoning arguments

Estimated Time:1m 15s

Question 11Question →

Ecologist: Subterranean mycorrhizal fungal networks can transport carbon and defensive biochemical compounds between established canopy trees and developing understory saplings. A forestry study monitored Douglas fir saplings planted within five meters of mature birch trees and compared them to saplings planted in open, cleared plots without neighboring trees. The saplings planted near birch trees grew thirty percent faster and exhibited significantly lower rates of foliar blight. The researchers concluded that subterranean nutrient and defense transfers through shared fungal networks from the birch trees directly account for the improved growth and blight resistance of these saplings.

Which of the following statements, if true, most seriously undermine the researchers' conclusion? (Select all that apply.)

Select all that apply

Douglas fir saplings whose root zones were isolated from nearby birch trees by subterranean impermeable mesh barriers that prevent fungal connections exhibited the same enhanced growth rates and blight resistance as connected saplings.

Isotopic tracing assays confirmed that substantial concentrations of carbon compounds synthesized by the mature birch trees were absorbed into the root vascular systems of the neighboring Douglas fir saplings.

The cleared plots used in the study had undergone heavy mechanical scraping that severely compacted the subsoil and stripped topsoil moisture, whereas the soil surrounding the mature birch trees remained loose and hydrated.

Douglas fir saplings planted in proximity to mature alder trees demonstrate even higher annual biomass gains than those planted near mature birch trees.

Foliar blight spores invariably kill every infected conifer sapling regardless of host nutritional status or general vigor.

Show answer & explanation

Answer: Douglas fir saplings whose root zones were isolated from nearby birch trees by subterranean impermeable mesh barriers that prevent fungal connections exhibited the same enhanced growth rates and blight resistance as connected saplings.; The cleared plots used in the study had undergone heavy mechanical scraping that severely compacted the subsoil and stripped topsoil moisture, whereas the soil surrounding the mature birch trees remained loose and hydrated.

Answer

The statements establishing that saplings isolated by subterranean mesh barriers still experience the same gains and that the cleared comparison plots suffered from severe soil compaction and degradation together undermine the conclusion.

The conclusion asserts a direct causal relationship: shared underground fungal networks transfer nutrients and signals, causing improved sapling growth and disease resistance. The statement showing that saplings separated by physical mesh barriers still exhibit identical benefits severs the causal mechanism by showing the effect occurs in the absence of the proposed cause. Additionally, the statement detailing severe soil compaction and degradation in the cleared plots provides an alternative explanation for the performance gap between the two test groups, undermining the claim that the birch trees were responsible.

Step-by-Step Solution

Isolate the argument's premises and main conclusion.

Premises establish that birch trees and fir saplings can share fungal networks, and saplings planted near birch trees grew faster and suffered less blight than saplings in cleared plots. Conclusion claims that underground nutrient and defense transfers through fungal networks directly cause these improvements.

Weaken questions require identifying the specific gap between the observed correlation in the premises and the causal claim in the conclusion.

Identify unstated assumptions and vulnerabilities in the causal inference.

The author assumes that the fungal network is the causal agent rather than aboveground microclimate factors (e.g., canopy shade), and that the cleared plots were otherwise identical in growing conditions to the soil near the birch trees.

Causal conclusions in observational field studies are vulnerable to confounding baseline differences and alternative causal pathways.

Evaluate each answer choice to identify those that break the causal link or introduce plausible alternative explanations.

The option showing identical benefits when fungal connections are physically blocked removes the proposed cause while the effect remains. The option describing degraded soil in the cleared plots introduces a confounding factor that accounts for the disparity.

Both findings directly invalidate the attribution of the effect to shared mycorrhizal transfers.

Key Concept

Evaluating Causal Arguments and Confounding Variables

Estimated Time:2m 15s

Question 12Question →

Linguist: In a multi-year study of bilingual children, researchers found that those who acquired their second language primarily through unstructured conversational immersion exhibited a significantly higher degree of grammatical flexibility and were more likely to generate novel linguistic structures than those who acquired it through formal classroom instruction. Because formal instruction relies heavily on the rote memorization of rigid syntactic rules, it is evident that such structured educational environments stifle the cognitive creativity naturally associated with language acquisition.

Which one of the following, if true, most seriously weakens the linguist's argument?

The grammatical flexibility exhibited by children in unstructured immersion environments often leads to frequent syntactical errors that require continuous correction.

Many formal language classrooms now incorporate substantial periods of unstructured conversational immersion into their curriculum alongside standard rule memorization.

Children who demonstrate a lower baseline aptitude for spontaneous linguistic pattern recognition are disproportionately channeled by educators into formal classroom instruction.

No educational environment, regardless of how rigidly structured its curriculum may be, can completely eliminate a child's innate cognitive creativity.

Formal classroom language instruction typically penalizes students for deviating from established grammatical models, thereby actively discouraging them from experimenting with novel linguistic structures.

Show answer & explanation

Answer: Children who demonstrate a lower baseline aptitude for spontaneous linguistic pattern recognition are disproportionately channeled by educators into formal classroom instruction.

Answer

Children who demonstrate a lower baseline aptitude for spontaneous linguistic pattern recognition are disproportionately channeled by educators into formal classroom instruction.

The linguist makes a massive causal leap from a simple correlation: because children in formal instruction exhibit less creativity, the instruction must be causing that lack of creativity. The correct answer highlights a severe selection bias by demonstrating that children who already lack a natural aptitude for spontaneous linguistic pattern recognition (a core element of the creativity being measured) are disproportionately placed into formal instruction. This provides a compelling alternative explanation for the study's results: the difference in creativity existed before the instruction even began. By providing an alternate cause for the phenomenon, it severs the causal link the linguist attempted to establish.

Step-by-Step Solution

Identify the main conclusion of the linguist's argument.

The conclusion is that structured educational environments (formal instruction) stifle the cognitive creativity associated with language acquisition.

Accurately targeting the conclusion is required to find the logical gap in a Weaken question.

Identify the premises supporting this conclusion.

The primary premise is a correlation: children in formal instruction exhibit less grammatical flexibility and produce fewer novel structures than children in immersion environments.

Understanding the evidence allows you to see how the author makes the leap from premise to conclusion.

Analyze the logical gap in the causal reasoning.

The author assumes that the educational environment is the CAUSE of the difference in creativity. The gap is the failure to consider alternative explanations, such as a pre-existing difference between the two groups of children.

Causal arguments based on observational studies are highly vulnerable to selection bias or reverse causality.

Evaluate the options to find one that attacks this specific gap.

The correct option reveals that children who already lack a natural aptitude for linguistic pattern recognition are selectively placed into formal instruction.

This alternative explanation accounts for the lower creativity in the formally instructed group without accepting the conclusion that the instruction itself caused the stifling, thereby dismantling the argument.

Key Concept

Causal Reasoning: Selection Bias and Alternative Explanations

Question 13Question →

Argument: To halt the depletion of the native Silverfin fish population, the regional fisheries agency replaced its length-of-season restrictions with a strict, industry-wide annual catch quota. Over the past three years, the total recorded weight of Silverfin caught has not exceeded the new quota limit, yet the overall Silverfin population has declined at a substantially faster rate than before. The agency concludes that the total allowable catch limit was set too high to enable the population to stabilize.

Statement: The argument is significantly weakened by the fact that the industry-wide nature of the quota incentivized fisheries to adopt non-selective drag netting to maximize their catch speed before the total quota is reached, resulting in massive, unrecorded deaths of pre-reproductive Silverfin.

True

False

Show answer & explanation

Answer: True

Answer

True. The provided statement accurately identifies a fact that undermines the agency's specific conclusion.

The statement correctly identifies that the new fact undermines the agency's conclusion. The agency concludes that the total catch limit was numerically too high. However, the new fact provides an alternative explanation for the population decline: the 'industry-wide' structure of the quota caused fisheries to change their methods, resulting in unrecorded juvenile deaths. This severs the causal link between the numerical height of the quota limit and the population decline, thereby weakening the argument.

Step-by-Step Solution

Analyze the stimulus to separate the premises from the main conclusion.

Premise: Recorded catch met the new quota, but the population declined faster. Conclusion: The numerical limit of the catch quota was set too high.

Identifying the exact conclusion is necessary to determine what specifically must be weakened.

Identify the logical gap or assumption in the agency's reasoning.

The agency assumes that the recorded catch is the only variable affecting the population and that the numerical limit is the primary cause of the continued decline.

Weaken questions require attacking the unstated assumptions bridging the premises and the conclusion.

Evaluate the impact of the new fact presented in the statement on the agency's conclusion.

The fact introduces an alternative cause: the structural design of the quota (industry-wide) caused unrecorded juvenile deaths via a new fishing method.

If an alternative cause explains the observed effect (population decline), it weakens the agency's claim that the limit itself was the cause.

Determine the final truth value of the statement.

Because the fact successfully introduces an alternative explanation that severs the agency's causal link, the statement that 'the argument is significantly weakened' is True.

This confirms the statement accurately evaluates the logical impact of the new fact.

Key Concept

Alternative Explanations and Causal Flaws

Question 14Question →

Consider the following argument: A municipal commuter rail system reported a 15 percent increase in passenger volume during the three months following the installation of free onboard Wi-Fi. The transit authority concluded that offering the complimentary Wi-Fi service was the primary reason for the surge in commuters.

Statement: The fact that a major parallel highway bridge was closed for emergency repairs during those exact same three months weakens the transit authority's conclusion.

True

False

Show answer & explanation

Answer: True

Answer

True: The statement accurately notes that introducing an alternate explanation for the increased ridership weakens the transit authority's causal claim.

The statement is true because the emergency highway closure offers an obvious alternate cause for the commuter surge, directly weakening the author's claim that onboard Wi-Fi was the primary driver.

Step-by-Step Solution

Identify the argument's premises and main conclusion.

Premise: Passenger numbers increased after Wi-Fi was added. Conclusion: Wi-Fi was the primary cause of the increase.

Isolating the causal link is necessary to determine what would undermine the argument.

Assess the logical impact of the supplementary statement.

The emergency closure of a major parallel highway provides an independent reason why drivers switched to the train during that exact period.

Providing a viable alternative cause for an observed effect directly weakens a causal conclusion.

Evaluate the truth value of the statement.

Because the alternate cause undermines the original causal attribution, the assertion that it weakens the argument is true.

The statement correctly classifies the weakening effect of the new evidence.

Key Concept

Weakening a causal conclusion by identifying an alternative explanation

Estimated Time:45s

Question 15Question →

Agricultural Scientist: Vineyards in the Aris Valley that planted crimson clover between vine rows experienced a 40 percent lower incidence of grapevine leafroll virus than vineyards maintaining bare soil. Because crimson clover attracts predatory lady beetles that feed voraciously on mealybugs, which are the sole vectors of leafroll virus, the clover reduces viral infection specifically by suppressing the mealybug population.

Statement: If true, the discovery that vineyards with crimson clover maintained average mealybug densities per vine identical to those in bare-soil vineyards weakens the agricultural scientist's argument.

True

False

Show answer & explanation

Answer: True

Answer

True, because evidence showing unchanged mealybug populations directly undermines the author's claim that clover reduces viral disease specifically by suppressing mealybug numbers.

The correct assessment is True because the scientist's conclusion specifically attributes the disease reduction to the suppression of mealybug populations. If clover vineyards had the exact same density of mealybugs as bare-soil vineyards, the reduction in disease transmission must be due to some other factor, thereby directly undermining the scientist's explanatory hypothesis.

Step-by-Step Solution

Identify the argument's premises and main conclusion

Premises: Clover vineyards had 40% less leafroll virus than bare-soil vineyards; clover attracts lady beetles that eat virus-carrying mealybugs. Main conclusion: Clover reduces viral infection specifically by suppressing mealybug populations.

Weaken questions require isolating the exact claim the author attempts to prove.

Analyze the causal mechanism connecting the premises to the conclusion

The author assumes that attracting lady beetles actually succeeded in reducing the mealybug population, which in turn reduced disease transmission.

Attacking the proposed intermediary mechanism is a standard way to weaken a causal argument.

Evaluate the impact of the supplementary statement

If mealybug densities were identical in both groups of vineyards, lady beetle predation did not decrease vector density, falsifying the claimed mechanism of action.

Showing that the hypothesized mechanism did not occur undermines the specific conclusion drawn.

Key Concept

Undermining a causal conclusion by providing evidence that the proposed causal mechanism did not occur.

Question 16Question →

Botanist: Mycorrhizal fungi networks (MFNs) connect the root systems of various plants in a forest environment. In a recent five-year study of a mature Douglas fir forest, isotopic carbon tracing revealed that significant amounts of carbon moved continuously from mature, canopy-dominant Douglas firs to nearby shaded Douglas fir seedlings via these MFNs. Furthermore, the seedlings connected to the MFN exhibited a 30 percent higher survival rate than similarly shaded seedlings that were isolated from the fungal network. Therefore, it is clear that mature trees actively allocate resources through MFNs specifically to ensure the survival of their own species' offspring in light-limited environments.

Which of the following statements, if true, most strongly weaken the botanist's argument? (Select all that apply)

Select all that apply

Studies on mixed-species forests indicate that carbon transferred through MFNs flows from canopy-dominant trees to nearby shaded seedlings of entirely different plant species at the same volume and rate.

When researchers experimentally severed the MFN connections between mature Douglas firs and their seedlings, the mature trees demonstrably altered their root exudation patterns to compensate for the lost pathway.

The fungi comprising the network actively extract carbon from mature trees to fuel their own subterranean expansion, with seedlings merely passively absorbing excess carbon that the fungi excrete into the surrounding soil.

Advances in soil analysis have shown that isotopic tracing can sometimes miscalculate the precise origin point of carbon if the surrounding soil contains exceptionally high levels of decaying organic matter.

Douglas fir seedlings cultivated in controlled laboratory settings without any fungal networks demonstrate significantly faster vertical growth than seedlings grown in natural, mature forests.

Show answer & explanation

Answer: Studies on mixed-species forests indicate that carbon transferred through MFNs flows from canopy-dominant trees to nearby shaded seedlings of entirely different plant species at the same volume and rate.; The fungi comprising the network actively extract carbon from mature trees to fuel their own subterranean expansion, with seedlings merely passively absorbing excess carbon that the fungi excrete into the surrounding soil.

Answer

The correct statements are the one indicating carbon flows to different species at the same rate, and the one indicating fungi actively extract the carbon while seedlings passively absorb it.

The conclusion makes two distinct causal claims based on the observed correlation: that the mature trees 'actively allocate' the resources, and that they do this 'specifically to ensure the survival of their own species'. The correct answers introduce new evidence that dismantles both claims. The statement about mixed-species forests shows that the transfer is indiscriminate, destroying the 'own species' motive. The statement about fungal extraction shows that the fungi, not the trees, are driving the mechanism, destroying the 'actively allocate' claim.

Step-by-Step Solution

Analyze the structure of the argument.

Premises: Carbon moves from mature trees to shaded seedlings via MFNs. Connected seedlings survive 30% more. Conclusion: Mature trees actively allocate resources specifically to ensure their own species' survival.

Deconstructing the argument into premises and conclusion is necessary to identify the logical gap.

Identify the logical gaps and assumptions.

The author assumes that the transfer of carbon implies 'active allocation' by the tree (rather than passive diffusion or fungal action) and assumes the intent is 'specifically to ensure the survival of their own species'.

Finding assumptions reveals the vulnerabilities where the argument can be weakened.

Evaluate the options for statements that attack these specific assumptions.

One correct choice attacks the 'own species' assumption by showing cross-species transfer. The other correct choice attacks the 'active allocation' assumption by showing the fungi are the active agents.

Correct weaken answers often introduce new information that severs the causal link assumed by the author.

Key Concept

Identifying alternative explanations and severing assumed causal relationships in a correlation.

Estimated Time:2m 30s

Question 17Question →

Agricultural Economist: A newly engineered wheat strain resists the devastating "rust" fungus. In ideal conditions, this resistant strain yields 10 percent less grain per acre than traditional varieties. Nevertheless, farmers in regions susceptible to rust should transition entirely to the new strain. Adopting this strain completely eliminates the need for chemical fungicides, which currently account for nearly a third of these farmers' annual operating costs. Therefore, by making this transition, these farmers will maximize their average net income over the next decade.

Which of the following, if true, most seriously weakens the agricultural economist's argument?

The chemical fungicides conventionally used to prevent rust also provide essential protection against several other yield-destroying pests to which the new wheat strain is highly vulnerable.

During years with heavy rainfall, which promotes severe rust outbreaks, traditional wheat varieties experience yield losses far exceeding 10 percent even when treated with fungicides.

In agricultural regions that are completely unaffected by the rust fungus, farmers who adopted the newly engineered strain reported a substantial decline in their overall net income.

The market price of the chemical fungicides used to combat rust has decreased slightly over the past two years due to global manufacturing innovations.

Consumer advocacy groups frequently launch public campaigns against genetically engineered crops, though historical data shows such campaigns rarely impact wholesale grain market prices.

Show answer & explanation

Answer: The chemical fungicides conventionally used to prevent rust also provide essential protection against several other yield-destroying pests to which the new wheat strain is highly vulnerable.

Answer

The option stating that the chemical fungicides provide essential protection against other yield-destroying pests to which the new strain is vulnerable.

The economist bases the conclusion on a straightforward cost-benefit calculation: saving nearly a third of operating costs will more than make up for a 10 percent drop in ideal yield. The correct answer shatters this calculation by showing that eliminating the fungicide has a massive unintended consequence. Because the fungicide also protects against other pests, and the new wheat is highly vulnerable to them, removing the chemical will result in catastrophic yield losses far beyond 10 percent, effectively preventing the farmers from maximizing their net income.

Step-by-Step Solution

Identify the conclusion and premises of the argument.

Conclusion: Transitioning to the new wheat strain will maximize farmers' average net income. Premises: The strain yields 10% less in ideal conditions, but it eliminates the need for fungicides that cost 1/3 of operating expenses.

Deconstructing the argument is necessary to isolate the core logical gap.

Determine the unstated assumption linking the premises to the conclusion.

The argument assumes that eliminating the fungicide is a pure cost-saving measure that will not introduce new, unforeseen costs or severe yield losses beyond the stated 10% baseline.

Identifying the assumption reveals how the argument can be logically attacked.

Evaluate the answer choices to find the one that attacks this assumption.

The correct option reveals that stopping the fungicide treatments removes protection against other pests, which will ravage the highly vulnerable new strain, thereby destroying the expected financial gains.

A valid weakener must introduce new information that severs the logical link between the proposed action and the expected outcome.

Key Concept

Causal and Conditional Reasoning in Cost-Benefit Analysis

Question 18Question →

Archaeologist: Recent excavations at the Bronze Age settlement of Tell el-Marra uncovered dozens of copper-alloy daggers containing significant concentrations of arsenic rather than tin. Because tin-copper bronze was markedly more durable than arsenical copper, and substantial tin ore deposits were located less than thirty kilometers from the settlement, the metalworkers at Tell el-Marra must have lacked the metallurgical knowledge required to smelt and alloy tin with copper.

Which of the following, if true, most seriously weakens the archaeologist's argument?

Surrounding settlements that maintained documented trade contact with Tell el-Marra routinely produced tin-copper bronze tools with sophisticated metallurgical alloying techniques.

In high-humidity climates, weapons crafted from arsenical copper retain their structural integrity and sharp cutting edges far longer than those made from tin-copper bronze.

The tin ore deposits located near Tell el-Marra were controlled by a hostile regional power that enforced an embargo prohibiting the settlement from mining or importing the ore.

Excavations at Tell el-Marra failed to recover the ceramic crucibles and stone casting molds that were standard equipment in Bronze Age foundries.

No ancient metalworkers ever developed the ability to smelt tin ores without first mastering the extraction and processing of arsenical copper.

Show answer & explanation

Answer: The tin ore deposits located near Tell el-Marra were controlled by a hostile regional power that enforced an embargo prohibiting the settlement from mining or importing the ore.

Answer

The option stating that the tin deposits near Tell el-Marra were controlled by a hostile regional power that enforced an embargo prohibiting access to the ore.

The correct answer provides an alternative explanation for why the metalworkers did not produce tin-copper bronze. The archaeologist infers a lack of technical competence solely from the fact that tin ore was geographically close yet unused. Showing that a hostile political entity blocked access to the deposit breaks the assumption of availability, demonstrating that a lack of raw materials rather than a lack of metallurgical skill explains the composition of the daggers.

Step-by-Step Solution

Analyze the structure of the argument to isolate the premises and the main conclusion.

Premises: Excavated daggers used arsenic instead of tin; tin bronze is mechanically superior to arsenical copper; tin ore was physically located within thirty kilometers. Conclusion: The metalworkers lacked the technical knowledge to smelt and alloy tin.

Deconstructing the argument into premises and conclusion is essential for identifying the logical vulnerability.

Identify the unstated assumption linking the premises to the conclusion.

The author assumes that because tin deposits were geographically close, the artisans had practical access to the ore, meaning that the only reason they did not use it was ignorance or lack of skill.

Weakening an argument requires exposing an unstated assumption or providing an alternative explanation for the observed facts.

Evaluate the answer choices to find the one that provides an alternative cause for the failure to use tin.

The statement showing that a hostile power blocked access to the nearby tin deposits proves that lack of physical access, not lack of metallurgical skill, prevented the use of tin.

Demonstrating an external barrier to resource acquisition directly undermines the conclusion that the artisans were technically incapable.

Key Concept

Causal Fallacy / Overlooked Alternative Explanation

Question 19Question →

City Planner: Last year, the municipal transport authority converted one general-traffic lane into a dedicated express bus lane along each of the city's four main arterial roads. Over the subsequent year, average bus commute times dropped by 18 percent, while average automobile travel times on those arterial roads remained completely unchanged. Thus, converting general-traffic lanes to dedicated bus lanes does not reduce the volume of automobile traffic an arterial roadway can accommodate without congestion.

Which of the following, if true, most seriously weakens the city planner's argument?

Automobile drivers using the arterial roads reported that overall traffic flow became more predictable after buses were restricted to dedicated lanes.

A municipal survey conducted prior to the lane conversion showed that a majority of local automobile commuters strongly opposed the reduction of general-traffic lanes.

During the twelve-month period following the lane conversion, a substantial proportion of automobile commuters who previously used the arterial roads diverted their daily routes to adjacent residential streets.

The automated traffic sensors used to record automobile travel times along the arterial roads were recalibrated once during the twelve-month monitoring period.

Whenever dedicated bus lanes are established in any metropolitan area, public transit passenger volume invariably increases by more than twenty percent.

Show answer & explanation

Answer: During the twelve-month period following the lane conversion, a substantial proportion of automobile commuters who previously used the arterial roads diverted their daily routes to adjacent residential streets.

Answer

The statement that many automobile commuters diverted their routes to adjacent residential streets most seriously weakens the argument.

The argument concludes that dedicated bus lanes do not diminish a roadway's automobile traffic capacity based on the evidence that automobile travel times did not increase. The correct choice weakens this claim by showing an alternate explanation for the constant travel times: a significant fraction of drivers diverted to residential side streets. Because fewer cars remained on the arterial roads, congestion did not increase, masking the loss of physical road capacity.

Step-by-Step Solution

Identify the premises and conclusion of the argument.

Premises: Converting one general lane to a bus lane decreased bus commute times by 18% and left car travel times unchanged on four arterial roads. Conclusion: Converting general lanes to bus lanes does not reduce the automobile traffic volume a roadway can handle without congestion.

Isolating the core reasoning reveals the gap between observed travel times and actual road capacity.

Identify the unstated assumption linking the premises to the conclusion.

The author assumes that the volume of automobile traffic attempting to use the arterial roads remained constant, meaning stable travel times must reflect unaltered road capacity.

Travel time is a function of both roadway capacity and total traffic volume.

Evaluate the answer choices for information that breaks this assumption.

If significant numbers of drivers avoided the arterial roads and diverted to residential streets, then the arterial roads handled fewer cars than before. This explains the unchanged travel times as a consequence of reduced demand rather than preserved capacity.

Providing an alternative explanation for the observed correlation directly severs the premise from the conclusion.

Key Concept

Alternative explanation for stable travel times (traffic displacement / spillover effect)

Estimated Time:1m 15s

Question 20Question →

Marine Biologist: Deep-sea glass squid possess photophores on their undersides that emit bioluminescence matching the wavelength and intensity of downwelling sunlight. In laboratory trials, whenever overhead light levels fluctuated, the squid immediately adjusted their ventral light emission to match. Because this counterillumination eliminates the squid's dark silhouette against surface waters, the squid must have evolved this adjustable bioluminescence primarily to evade predators that hunt by looking upward.

Which of the following, if true, most seriously weakens the marine biologist's argument?

In laboratory conditions using artificial lighting, ventral photophores fail to replicate the exact spectral distribution of sunlight penetrating ocean waters.

Deep-sea predatory fish that regularly feed on glass squid possess specialized tubular eyes oriented almost exclusively toward the ocean surface.

The primary prey of deep-sea glass squid consists of small fish whose upward-pointing eyes detect overhead silhouettes, prompting them to flee before the squid can capture them.

All marine organisms residing at ocean depths below the maximum reach of downwelling sunlight lack ventral photophores entirely.

Several related species of shallow-water cephalopods rely on dynamic chromatophore pigmentation rather than bioluminescence for camouflage.

Show answer & explanation

Answer: The primary prey of deep-sea glass squid consists of small fish whose upward-pointing eyes detect overhead silhouettes, prompting them to flee before the squid can capture them.

Answer

The finding that the squid's primary prey possesses upward-pointing eyes and flees upon detecting overhead silhouettes.

The argument concludes that adjustable counterillumination evolved primarily for defense against upward-looking predators based solely on the fact that it eliminates the squid's downward silhouette. The correct answer weakens this conclusion by presenting an alternative explanation: the squid's prey also looks upward to detect silhouettes and escape. If eliminating the silhouette is essential for successfully catching food, the trait may have evolved primarily for predation rather than defense.

Step-by-Step Solution

Identify the argument's premises and main conclusion

Premises establish that glass squid adjust ventral bioluminescence to match downward sunlight and eliminate their silhouette. Conclusion asserts that this trait evolved primarily to evade predators hunting from below.

Deconstructing the argument isolates the core causal claim: that predator evasion is the primary evolutionary reason for counterillumination.

Identify the underlying assumption or logical gap

The author assumes that because eliminating a silhouette conceals the squid from viewers below, the selective pressure driving this adaptation came from predators rather than another selective advantage, such as capturing prey.

Weakening a causal or teleological conclusion typically requires introducing an alternative explanation for the observed adaptation.

Evaluate the choices to find the one providing a strong alternative explanation

Demonstrating that the squid's prey relies on detecting overhead silhouettes to escape provides a direct alternative purpose: offensive camouflage for hunting.

An alternative evolutionary function directly undermines the claim that the trait evolved primarily for predator evasion.

Key Concept

Alternative Causal Explanations in Evolutionary Arguments

Estimated Time:1m 15s

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