LSAT 132 | Section 4 | Logical Reasoning: Q18

LR Question 18 Explanation

QUESTION TEXT: If there are sentient beings on planets outside our…

QUESTION TYPE: Sufficient Assumption

CONCLUSION: We won’t know if there are aliens outside our solar system unless the aliens are as smart as us.

REASONING:

1. We can’t send spaceships to aliens.
2. If aliens were to send us messages, they’d have to be at least as smart as us.

ANALYSIS: I simplified the language in the conclusion/reasoning to make the argument clearer.

Now, you first must find the flaw, so your job is to imagine an alternate possibility. Pretend someone is paying you $50 to spot the flaw in this argument. Is there any other way we could figure out aliens exist, even if we can’t travel to them or receive messages?

Well, what about a telescope? There are other ways to discover what’s in the universe. The argument’s flaw is assuming that the two possibilities it gave are the only two possibilities for discovering aliens.

This is a sufficient assumption question, so you must prove this argument correct. The argument works if you assume that there are no other ways to discover the aliens. Then the argument will be correct. (This almost is a necessary assumption question)

Note that the argument is only talking about aliens outside the solar system. Note also that diagrams are not useful on this question, so I haven’t drawn any.

___________

1. The argument is talking about aliens outside the solar system. This answer is irrelevant.
2. The argument wasn’t saying that aliens will communicate with us if they’re as intelligent as us. The argument is saying that the only way we could possibly discover aliens is if they communicated with us.
3. The stimulus already said we can’t send spaceships to planets outside our solar system. Since the conclusion is only about aliens on planets outside the solar system, this answer doesn’t help.
4. CORRECT. This says that there are only two possibilities for discovering aliens:
   1. We send a spaceship.
   2. They communicate with us.
   The argument already eliminated the first possibility. And the second possibility only works if aliens are as smart as us. So this answer proves that the only way we’ll discover aliens outside our solar system is if they’re at least as smart as us.
5. This gets things backwards. The argument didn’t say that we’d definitely hear from aliens if they were at least as smart as us. It said that we’d only hear from aliens if they were at least as smart as us.
   So this answer adds nothing. We’re trying to prove that sentient aliens are the only possibility for communication. So we need to show there are no other possibilities. Whether or not aliens actually do or can communicate with us doesn’t matter.

Recap: The question begins with “If there are sentient beings”. It is a Sufficient Assumption question. To practice more Sufficient Assumption questions, have a look at the LSAT Questions by Type page.