PrepTest 139, Section 1, Question 14
Investigators have not proved that the forest fire(28 more words not shown)
The flawed pattern of reasoning(19 more words not shown)
- AKim has no(38 more words not shown)
- BWe have no(35 more words not shown)
- CMost of the(34 more words not shown)
- DIn some parts(32 more words not shown)
- EThe evidence shows(55 more words not shown)
Reading the argument
Maybe the investigators have narrowed it down to these two causes.
They could know the fire was caused by either campers or lightning without knowing which one. Imagine they've ruled out every other possible cause but can't distinguish these last two. They haven't proved campers did it, and they haven't proved lightning did it. Yet they have proved that one of those two caused the fire.
That's the mistake: lacking proof of each individual option doesn't mean lacking proof of the two-option claim. Be careful about the conclusion. It says the investigators haven't proved “campers or lightning.” It doesn't say they've proved that neither caused the fire.
What we’re looking for
For the matching flaw, look for two possibilities, no support settling either one individually, and an unjustified claim that there is no support for one or the other. The distinction between choosing a particular option and narrowing the possibilities to a pair is what matters.
Working the answers
- ACorrect
Sada corresponds to the campers, and Brown corresponds to lightning. Kim lacks a reason to pick either candidate individually, then concludes she has no reason to believe one or the other will win. But what if Sada and Brown are the only two candidates? Kim could know the winner must be one of them without knowing which one. That's the same gap between identifying an individual possibility and establishing the pair.
- B
This starts similarly: neither escape theory has been proved. But its conclusion is that the theories are equally plausible. Our argument doesn't compare the likelihood of campers and lightning. To match, B would need to conclude that there is no proof the thief escaped through either of the two routes.
- C
This combines two majority claims and makes an unsupported claim about their overlap. Most residents are engineering majors and most are from out of town, but the out-of-town residents need not make up most of the engineers. That's a mistake about proportions within groups, not about what can be proved concerning two possible explanations.
- D
Camping might be permitted in one part of the forest and hunting in a completely different part. D wrongly assumes the two areas overlap. It doesn't discuss uncertainty about which of two explanations is true, or distinguish proof of a pair from proof of an individual option.
- E
Evidence allowing Jones as a possible driver and Katsarakis as a possible driver doesn't necessarily allow both to have driven at the time of the accident. E moves from each being possible separately to both being possible together. The fire argument instead moves from lacking proof of either cause individually to lacking proof that one or the other was responsible.
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