LSAT 114 | Section 2 | Logical Reasoning: Q25

LR Question 25 Explanation

QUESTION TEXT: In our solar system only one of the nine planets-Earth-qualifies…

QUESTION TYPE: Necessary Assumption/Flawed Reasoning

CONCLUSION: The total number of planets fit to sustain life must be enormous.

REASONING: One out of nine planets in our solar system is fit to sustain life. And there a lot of planets in the universe. If we presume that one out of nine of them can sustain life…

ANALYSIS: This is a bad argument because it assumes that the ratio in our solar system (of planets that can sustain life) is the same for all of the other planets in the Universe. But it could be that the 1/9 ratio isn’t true everywhere and practically no planets can sustain life.

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1. This goes further than the argument. The argument only claimed that planets will be fit to sustain life. They might not actually have life. And it didn’t say anything about planets being Earthlike.
2. CORRECT. The argument is assuming that at least “many” solar systems are like ours. 
3. Even if the conditions aren’t well understood we definitely know that Earth can sustain life. We can presume there might be other planets like Earth without knowing exactly what the other planets need.
4. Even if this weren’t true it could still be the case that many planets could sustain life. It could exist in different forms.
5. It isn’t necessary that the other systems have nine planets. It’s just necessary that they have similar ratios. (E.g. if there are 18 planets then 2 could sustain life.)