Supply the missing premise that makes the conclusion follow logically:P: X–some–YP: ?C: Z–some–Y
gharibiannickFebruary 27, 2020
Clarification on flipping premise & conclusion
P: X some Y
P:
C: Z some Y
I concluded that I needed to see both X and Z. This didn't affect any of the answer choices. Then I thought answer should be Z ->X because then it would lineup like this:
Z-X-some-Y
I'm having trouble understanding why this is wrong even though after I knew it didn't sound nor look right. Does the some change the way we come to find the answer ?
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I think I can explain this better if I use an example. But, to briefly describe your mistake: Z - - - -> X - - some - - Y leaves room for the possibility that no Zs are also Y. We know that some Xs are Y, but we do not know which. It could be none of the Xs that are Z. I know that is confusing, so I think this example will help.
X = Dogs Y = >50 pounds Z = Terriers
Premise 1: Some dogs (X) weigh more than 50 pounds (Y). X - - some - - Y
Premise 2: ?
Conclusion: Some terriers (Z) weigh more than 50 pounds (Y). Z - - some - - Y
What premise can I use to get to this conclusion? I will try it your way first: Z - - > X - - some - - Y Using my example: Terrier (Z) - - - -> Dog (X) - - some - - >50 (Y)
A terrier is a dog, and some dogs weigh more than 50 pounds. Does this prove that some terriers weigh more than 50 pounds (Z - - some - - Y)? No! It could still be true that all terriers are dogs, and some dogs weigh more than 50 pounds. But those dogs might be only rottweilers.
The correct answer would be X - - > Z, or Dog - - -> Terrier. If all dogs are terriers, then some terriers are definitely over 50 pounds. (Obviously in the real world this is not true, but in the LSAT world this is valid reasoning.)
Dog (X) - - - - - -> Terrier (Z) Dog (X) - - some - - >50 (Y)
We have an "all" statement and a "some" statement about dogs. There must be some overlap between Y and Z, giving us our conclusion.
