PrepTest 154, Section 1, Question 25
Each major earthquake in this region has been(29 more words not shown)
Which one of the following(16 more words not shown)
- AIn the past,(35 more words not shown)
- BThis river has(29 more words not shown)
- COn planets other(37 more words not shown)
- DThe introduction of(36 more words not shown)
- ESo far, all(41 more words not shown)
Reading the argument
Perhaps the small tremors stop without a major earthquake.
Every major earthquake in the record had minor tremors before it. That doesn't tell us what happened after every series of minor tremors. Some could have been followed by a major quake; others could have led to nothing bigger. The author has treated a pattern found before major earthquakes as a guarantee that one is coming.
What we’re looking for
For the parallel flaw, keep track of which event the word “every” describes. We want: every big event was preceded by a warning sign; the warning sign appears now; therefore the big event will happen. We don't want a premise that already tells us every warning sign produces the big event. That would give the conclusion support the earthquake argument lacks.
Working the answers
- A
This starts with every tropical storm resulting in a hurricane, rather than every hurricane having a tropical storm before it. It then reasons from no tropical storm to no hurricane. The original observes the warning sign and predicts the outcome; A observes the absence of its starting event and denies the outcome. Both the stated relationship and the final move differ.
- B
This is initially tempting. High snowfall could be our minor tremors, and a flood could be our major earthquake. But reread the first sentence: the river overflowed after every winter with high snowfall. So each occurrence of the supposed warning has been followed by the outcome.
Our argument tells us something different: each major earthquake had the warning beforehand. To match it, B would need to say every flood had been preceded by a snowy winter, then use this snowy winter to predict a flood. Instead, B's evidence already tracks what followed snowy winters. The same topics in the right-looking order can hide a different relationship.
- C
This applies an indication found on other planets to Earth. Its question is whether the same minerals support the same conclusion in a different setting. It doesn't say every bombardment was preceded by minerals, observe minerals now, and predict a future bombardment. That would be the warning-to-event pattern we need.
- D
Here the first sentence explicitly guarantees the outcome: introducing non-native species always results in some native extinction. We are then told that non-native species are being introduced, so the stated result follows. The earthquake argument never gives an equivalent guarantee that every tremor sequence produces a major quake. D is therefore missing the flaw.
- ECorrect
Human outbreaks correspond to major earthquakes. Detected high infection rates in wildlife correspond to the minor tremors. Every past human outbreak was preceded by the wildlife warning; now that warning appears again, so the author predicts a human outbreak.
But high wildlife infection might occur without a human outbreak, just as minor tremors might occur without a major earthquake. E never establishes that every appearance of the warning leads to the outcome. It makes the same unsupported jump from something found before past events to a guarantee of the next one.
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