Practice bank
Critical reasoning: weaken a causal claim
VerbalCritical reasoningMedium
A coffee shop's monthly sales rose 20 percent in the three months after it began offering free wifi. The owner concludes that the free wifi caused the increase. Which of the following, if true, most weakens the owner's conclusion?
- ASome regular customers say they appreciate the free wifi.
- BA large university opened a new campus across the street from the shop at about the same time the wifi was introduced.
- CTwo other coffee shops in the neighborhood also offer free wifi.
- DThe shop raised its prices on pastries slightly the previous year.
- EProviding free wifi costs the shop very little each month.
Try it before you scroll. Two minutes on the clock, then commit to an answer.
Correct answer: B
The owner’s evidence is pure sequence: sales rose after wifi arrived. The conclusion turns “after” into “because of.” The standard way to weaken that move is to supply an alternative cause for the same increase.
- (B) does exactly that. A new university campus across the street delivers a large new customer pool at precisely the time sales jumped, which explains the 20 percent without the wifi. Correct.
- (A) mildly supports the wifi story, or is simply irrelevant: appreciation by some regulars does not explain new revenue.
- (C) might suggest wifi is common, but it does nothing to explain this shop’s timing. If anything, competitors with wifi make the shop’s gain more surprising, not less attributable.
- (D) concerns the previous year, outside the three-month window, and higher prices would if anything depress sales.
- (E) addresses cost, not causation. Cheap wifi can still be ineffective wifi.
The pattern to memorize: post hoc arguments (X happened, then Y happened, so X caused Y) are weakened by alternative causes, and strengthened by ruling alternatives out. When you spot the post hoc structure, scan the choices for a rival explanation first.