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Difficulty: HardNecessary Assumption

Agricultural economist: The newly developed cultivar of soybean, "Drought-Shield", requires 30 percent less irrigation water per hectare than the conventional soybean varieties currently grown in the arid central valley. Conventional soybeans currently account for over 70 percent of the central valley's agricultural water use. Therefore, if central valley farmers entirely replace their conventional soybeans with Drought-Shield, the central valley's total agricultural water consumption will decline substantially.

Which one of the following is an assumption on which the agricultural economist's argument depends?

  1. A
    Drought-Shield soybeans are at least as profitable for central valley farmers to cultivate as conventional soybean varieties.
  2. B
    A 30 percent decrease in the per-hectare water required for soybean cultivation will result in a 30 percent decrease in the central valley's overall agricultural water consumption.
  3. C
    Conventional soybeans are currently the most water-intensive crop per hectare cultivated by farmers in the central valley.
  4. Central valley farmers will not increase the total number of hectares devoted to soybean cultivation to such an extent that it negates the per-hectare reduction in water use.Answer
  5. E
    Replacing conventional soybeans with Drought-Shield is the only viable method for central valley farmers to substantially reduce their total agricultural water consumption.

Answer

The argument assumes that farmers will not increase their total soybean acreage enough to negate the per-hectare water savings.
The argument shifts from a per-hectare reduction (a rate) to a total consumption reduction (an absolute amount). For a reduction in rate to guarantee a reduction in total amount, the underlying base (the total number of hectares cultivated) cannot increase enough to offset the efficiency gains. By applying the Negation Test, if farmers *did* increase their soybean acreage to such an extent that it negated the per-hectare reduction, total agricultural water consumption would not decline substantially, and the argument would fail. Therefore, this assumption is strictly necessary.

Step-by-Step Solution

1
Identify the core argument structure.
Premises: Drought-Shield uses 30% less water per hectare, and current soybeans account for over 70% of total agricultural water. Conclusion: If farmers switch entirely to Drought-Shield, total agricultural water use will decline substantially.
Deconstructing the argument structure is necessary to isolate the logical gap.
2
Analyze the logical gap between the premises and the conclusion.
The premises provide a reduction in a rate (water per hectare) and infer a reduction in an absolute amount (total water consumption).
Identifying shifts between rates and absolute numbers reveals potential flaws in the reasoning.
3
Anticipate a necessary assumption that bridges this gap.
The argument must assume that the total number of hectares planted will not increase so dramatically that it wipes out the efficiency savings gained per hectare.
If total acreage increases significantly, total water use could stay the same or rise, destroying the conclusion.
4
Apply the Negation Test to the anticipated assumption.
Negating the correct option yields: 'Farmers WILL increase soybean acreage to such an extent that it negates the per-hectare savings.' This directly invalidates the conclusion.
The Negation Test definitively proves whether an assumption is strictly necessary for the argument to hold.

Key Concept

Identifying a 'Defender' assumption that prevents a flaw related to rates versus absolute amounts.
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Topics

Necessary Assumption

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