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#4 - If a civilization as technologically advanced as human

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Please post below with any questions!
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I see why D "A technologically advanced civilization on another planet would want to communicate with intelligent life that it detected on Earth" is a necessary assumption for the conclusion to be valid. However, I am not certain why E "Intelligent life forms on other planets would be able to recognize all signs of intelligent life on Earth" is not also a necessary assumption? Is it perhaps because the stimulus states that "that civilization would have found evidence of intelligent life on Earth" so this is already an explicit premise and therefore cannot be an assumption made by the argument?

Would appreciate your feedback!
Jonathan Evans
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Good question! Actually the issue has to do with the categorical statement in this answer choice, the use of the quantity word "all." It is not necessary that an extraterrestrial intelligence recognize all signs of intelligent life on earth. Consider the Negation Test here. Negated, this statement would be "extraterrestrial intelligence does not recognize all signs of intelligent life on earth." Clearly, this extraterrestrial intelligence could still recognize some signs of intelligent life on earth. Indeed, as you mentioned, its ability to recognize some of these signs is a premise of this argument! Therefore, there is no assumption about whether such an intelligence recognizes all or only some signs of intelligent life on earth.

On your work on Assumption problems such as these, focus on identifying the gap between the premises and the conclusion. Focus on the claim: There is no technologically advanced alien intelligence within 50 light years. Why not? Because such an intelligence would have been able to detect intelligence on earth and could have contacted us.

Now to prephrase, where's the gap? Just because this intelligence could have contacted us, the author provides no intelligence that the would actually do so.

I hope this helps!
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I understood how D could be the correct answer, but I am wondering how come C isn't a good answer. Is it because of the word "fully" because I understood utilizing the negation technique that basically those on earth searching for the signal would be unable to decipher it (and thus wouldn't receive it)? Thank you!
Adam Tyson
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"Fully" is part of the problem, Jenna, but also "decipher" is not the same as "receive". We might get an indecipherable message and still recognize that it is a message of some sort. Our ability to decipher the message is irrelevant to this question. Consider ancient hieroglyphs that remain hard for us to read yet are clearly recognizable as telling a story or recording information.

The negation of answer C is that they would not be able to decipher it fully, rather than that they could not decipher it at all, but neither of those hurts the argument because deciphering simply doesn't matter, only receiving.

Keep at it!
Adam M. Tyson
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