Logical Reasoning

PT139 · S1 · Q14 Investigators have not proved

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Investigators have not proved that the forest fire was started by campers.

Therefore (So)

The investigators have not proved that the blaze was caused by campers or lightning.

Evidence

The investigators haven't proved that the forest fire was started by campers, nor have they proved it was started by lightning.

Evaluate

At first it seems like this conclusion is pretty reasonable, right?

Given that ... they haven't proved the fire was from campers and haven't proved the fire was from lightning,

How could we say that ... they have proved that fire was caused by campers or lightning?

Can you prove that "X or Y" is true even though you haven't proven that X or Y separately are true?

I guess so. There might be only two suspects at the scene of the crime. If you know someone committed an act of graffiti on the night of March 10, and you can prove that the only people who were there the night of March 10 were Sam and Pam, then you've proven that , even though you can't prove that it was Sam and can't prove that it was Pam.

Goal

In a sense this is a Part vs. Whole flaw. Since each part of "campers or lightning" has the trait "haven't been proven to be responsible for fire", the author assumes that the collective "campers or lightning" also shares that trait.

But it's a weird manifestation of Part vs. Whole, so it might be easier to just look for a similar conversational objection:

Even though we can't prove it's thing X vs. thing Y, it still might be possible that we're sure it had to be one of those two.

14.

The flawed pattern of reasoning in which one of the following arguments most closely resembles the flawed pattern of reasoning in the argument above?

Correct
Kim has no reason to
Why this is right
This seems somewhat similar to the original argument. It's possible that Kim and Sada are tied in the polls (they're each getting 40% of the vote) and then no other candidate has as much as 10% of the vote. Since they're tied in the polls, we have no reason to prefer one over the other. But since they are the two front-runners, we still have some reason to believe the winner will be one or the other of them. This answer doesn't seem perfect: this evidence is about having no reason at all to believe X, whereas the original argument is about not being able to prove X. Those are different. So we would bail from this if we were offered a tighter match, but we aren't.
Skill tested: Parallel Flaw · how this choice captures the argument's function is the move to repeat next time.
87% picked this
We have no proof either
Bad Conclusion Match
This has the right setup ingredients, but the conclusion should be saying, "Therefore, we have no proof that the thief escaped through the vent or the through the window".
5% picked this
Most of the students in
Different Flaw
This is a flaw relating to combining two Most statements. These two premises would allow us to say that, "some engineering majors are from out of town", but they don't allow us to get so precise as to say "most engineering majors in my dorm are from out of town". But the original argument has nothing to do with combining Most claims in an overly ambitious way.
1% picked this
In some parts of the
Different Flaw
Like (C), this flaw relates to trying to conclude some Venn Diagram overlap that is stronger than anything we can prove. Since each premise here just talked about Some parts of the forest, we have no reason to think that the camping parts have to overlap with the hunting parts. But the original argument had nothing to do with assuming there was an overlap between two Some statements.
2% picked this
The evidence shows that the
Different Flaw
The original argument was P1: Haven't proven X. P2: Haven't proven Y. C: Thus, haven't proven X or Y This answer's argument looks like this P1: Could have been X. P2: Could have been Y. C: Thus, could have been X and Y For the original, we were saying, "even though you can't prove it separately, maybe you can prove it together". For this, we're saying, "even though it could have happened separately, maybe it couldn't have happened together."
5% picked this

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