PrepTest 124, Section 2, Question 20
On some hot days the smog in Hillview(36 more words not shown)
The reasoning in the argument(6 more words not shown)
- Amistakes a condition(17 more words not shown)
- Bfails to recognize(28 more words not shown)
- Cuses the key(15 more words not shown)
- Dcontains a premise(11 more words not shown)
- Einfers a particular(15 more words not shown)
Reading the argument
What if those are different hot days?
Some hot days have unsafe smog. Some hot days have wind from the east. We haven't been told that either group includes all hot days, or even most of them. The word “some” leaves plenty of room for the two groups to miss each other entirely.
Imagine that Monday and Tuesday are both hot. Monday has unsafe smog with no east wind; Tuesday has east wind with safe smog levels. Both premises are true, but the conclusion doesn't follow. Think of the same mistake with a larger category: some days in Texas are extremely hot, and some are snowy. Those descriptions could refer to separate summer and winter days. Belonging to the same broad group doesn't force the smaller groups to overlap.
What we’re looking for
For the flaw question, that's the prediction: the argument assumes an overlap it hasn't established. We aren't proving that east wind and unsafe smog never occur together. We're showing that the two facts about hot days don't prove they ever do.
Working the answers
- A
The conclusion doesn't say anything must always accompany unsafe smog. It claims only that unsafe smog and east wind occur together on some days. That claim is still unsupported, but it isn't the move from sometimes to necessarily that A describes.
- BCorrect
Translate the three sets. One set is hot days. It has some days in common with the unsafe-smog set and some days in common with the east-wind set. Those could be entirely different days.
In the Monday/Tuesday example, hot days overlap each of the other groups, but the smog and wind groups don't overlap each other. B describes exactly the possibility the argument fails to consider.
- C
“Unsafe” refers to unsafe smog levels throughout. The author doesn't change from, say, an unsafe computer system to unsafe air while pretending the meanings match. The issue is which days belong to which groups, not a changed meaning of the word.
- D
Neither premise needs the conclusion to be true. Our example shows how we could have both hot-smog days and hot-east-wind days even if smog and east wind never coincided. The argument draws too much from independently acceptable premises; it doesn't support a premise by assuming the conclusion.
- E
No cause is proposed. The conclusion says east wind and unsafe smog sometimes occur together, not that the wind causes the smog or the smog causes the wind. We haven't established even that overlap, but the error isn't inferring a causal relationship from it.
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