Each excerpt below presents an academic argument that relies on an unstated premise. Match each argument with the implicit assumption on which its conclusion necessarily depends.
- Marine Geochemist: Benthic foraminifera shells preserved in deep-sea sediment cores show marked spikes in barium-to-calcium ratios specifically during deglaciation phases. Because continental river runoff is the primary global source of dissolved barium entering ocean basins, pulses of intense glacial meltwater discharge must have reached the deep abyss during these climate transitions.The elevated barium concentrations recorded in deep-sea foraminifera shells were not primarily the result of post-depositional chemical migration within the seafloor sediments.
- Phonologist: Infants raised in bilingual households maintain the ability to distinguish non-native tonal contrasts significantly longer into infancy than do infants raised in monolingual households. Because exposure to diverse acoustic pitch contours is known to delay perceptual narrowing, infant-directed speech in bilingual environments must possess acoustic pitch variations that monolingual speech lacks.The prolonged retention of tonal discrimination in bilingual infants is not predominantly driven by domain-general attentional adaptations that arise from navigating two linguistic systems.
- Economist: Following a municipal fee levied on single-use beverage containers, discarded container litter along public riverbanks dropped by 40 percent in six months. Because municipal sanitation schedules and cleanup budgets remained completely unchanged, the fee must have successfully motivated consumers to curtail their container usage or utilize proper recycling receptacles.The observed decline in riverbank container debris was not largely caused by third-party collectors gathering the discarded containers to salvage material value.
Answer
Each argument correctly matches its corresponding defender assumption: the marine geochemistry argument depends on the assumption that sediment chemical alteration did not produce the barium signal; the phonology argument depends on the assumption that non-acoustic cognitive mechanisms did not cause the perceptual delay; and the economics argument depends on the assumption that third-party collectors did not remove the litter after disposal.
For each pair, the right-hand statement functions as a vital defender assumption. Applying the Negation Test confirms their necessity: if post-depositional seafloor processes created the barium spikes, the geochemist's inference that surface meltwater penetrated the abyss is unsupported; if domain-general attention accounts for prolonged tonal discrimination, the phonologist's claim about acoustic properties in bilingual speech is unjustified; if third-party salvagers cleaned up the cans, the economist's claim regarding changed consumer habits is unwarranted.
Step-by-Step Solution
Key Concept
Necessary Assumption (Defender Model and the Negation Test)
Estimated Time:1m 30s