LSAT 79, Logical Reasoning I, Q4, LSATHacks

QUESTION TEXT: If a civilization as technologically advanced as…

QUESTION TYPE: Necessary Assumption

CONCLUSION: Scientists can safely say that no technologically advanced intelligent life exists within 50 light years of earth.

REASONING: If a civilization like ours existed within 50 light years of earth, that civilization could have detected us, and contacted us. If it wanted to.

ANALYSIS: The author misses the final point in the reasoning. Contact could have happened if the civilization wanted to. But, the argument doesn’t (and can’t) give us evidence about what aliens want.

So, the only conclusion we could have supported would have been: “Scientists can safely say that no technologically advanced civilization exists within 50 light years of us and wants to contact us.”

___________

1. This mixes things up. It’s not humans who have evidence of aliens. The stimulus is saying that if aliens existed nearby, those aliens would have evidence of us. 
2. This contradicts the argument. The author does give us reason to doubt that technologically advanced aliens exist: they haven’t contacted us.
3. We haven’t received a message. And the argument’s conclusion is that we never will, because no nearby aliens exist!
4. CORRECT. This is the crucial assumption. If there were aliens that didn’t want to communicate with us, then that would wreck the argument by providing an alternate explanation for why we haven’t heard from them.
   Negation: Technologically advanced civilizations on another planet would not want to communicate with us.
5. Negating all to “not all” is rarely significant, because you can negate it to 99.9999%
   Negation: Intelligent life on another planet would be able to recognize 99.999999% of signs of intelligent life on earth, but not all of them.

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