Practice bank
Critical reasoning: find the necessary assumption
VerbalCritical reasoningMedium
Mayor: "Our city will adopt the door-to-door recycling program used in three neighboring cities. Landfill waste fell in each of those cities after adoption, so our city's landfill waste will fall too." The mayor's argument depends on which of the following assumptions?
- AThe neighboring cities' programs were funded entirely by state grants.
- BOur city currently sends more waste per capita to landfills than its neighbors do.
- CThe conditions that allowed the program to reduce landfill waste in the neighboring cities also hold in the mayor's city.
- DDoor-to-door recycling is the only effective method of reducing landfill waste.
- EA majority of the mayor's constituents already support the program.
Try it before you scroll. Two minutes on the clock, then commit to an answer.
Correct answer: C
The argument is an analogy: it worked there, so it will work here. Every analogy argument silently assumes the two cases are similar in the ways that matter. That is exactly what (C) states. If the conditions that produced the reduction elsewhere (participation rates, landfill pricing, collection logistics) do not hold here, the conclusion collapses.
The negation test confirms it: if the conditions that allowed the reduction do NOT hold in the mayor’s city, the prediction that waste will fall loses its support. The argument needs (C).
Why the others fail:
- (A) introduces funding, which the argument never relies on. The mayor could fund the program any way at all and the analogy would stand or fall on the same grounds.
- (B) compares current waste levels, but the conclusion is about a decrease, not about who produces more. The analogy works whether the city starts above or below its neighbors.
- (D) is far stronger than needed. The mayor claims this program will reduce waste, not that it is the only method that could. Arguments need sufficient assumptions, not extreme ones.
- (E) confuses popularity with effectiveness. Support might help adoption, but the argument’s logic rests on the neighboring results, not on polling.