- PowerScore Staff
- Posts: 8950
- Joined: Feb 02, 2011
- Tue Nov 20, 2012 12:00 am
#37546
Complete Question Explanation
Flaw in the Reasoning, SN. The correct answer choice is (B)
The stimulus features conditional reasoning, which is identifiable by the use of the necessary condition indicator “only if” in the third sentence. The argument has the following structure:
Note that even though the journalist qualifies her conclusion with the word “likely,” her argument is still flawed, because satisfying a condition necessary for a certain event to occur only ensures that the event can occur, not that it is likely to occur. Because the author mistakes a necessary condition for a sufficient condition, the correct answer choice will probably use at least one of these key words (or their synonyms) to describe the error in conditional reasoning. This gives savvy test takers an advantage: if you identify a stimulus with conditional reasoning and are asked a Flaw question, quickly scan the answers and identify those that contain such key words as “sufficient,” “necessary,” or both. Although this approach may not eliminate all four incorrect answers, it usually helps narrow down the number of possible contenders.
Answer choice (A): At first glance, this seems to be an attractive answer, since it does focus on the conditional aspect of this argument and uses the word “necessary,” which we expect to find in the correct answer. However, upon close inspection you should notice that this answer choice does not describe a Mistaken Reversal, but the contrapositive: if a condition is necessary for the evolution of life (liquid water), then life cannot evolve if this condition is not met (i.e. if there is no liquid water). This is a classic description of a contrapositive statement, and does not describe a Flaw in the reasoning.
Remember—although the word “necessary” makes this answer choice attractive, test makers often exploit what students perceive to be “shortcuts” and turn them into traps. To avoid falling into this one, you must prephrase and look for an answer describing a Mistaken Reversal. Although it would be acceptable to flag answer choice (A) as a contender, make sure to read all five answers before making your choice. Ultimately, only (A) and (B) contain the key words we are looking for (“sufficient,” “necessary”), and a more careful comparison between the two reveals that (B) contains the proper description of a Mistaken Reversal, whereas (A) describes a logically valid argument.
Answer choice (B): This is the correct answer choice. By confusing a necessary condition for a sufficient one, the journalist ignores the possibility that liquid water may not be the only condition necessary for the evolution of life. If other requirements need to be met before a planet can support life, then having liquid water on Europa does little to increase the likelihood that primitive life has evolved there.
Note that there are multiple ways to describe the same flaw in conditional reasoning. Compare the following examples, all of which amount to the same description of a Mistaken Reversal:
Because there are so many ways to describe a conditional reasoning flaw, it is important to prephrase an answer describing a Mistaken Reversal but keep an open mind—do not let yourself get “boxed in” by the exact language of your prephrase.
Answer choice (C): The stimulus contains no evidence suggesting that life is likely to be present on Europa if, but only if, life evolved on Europa. Both the premise and the conclusion focus on the conditions necessary (or sufficient) for life to evolve on Europa, not whether such evolution is a necessary or a sufficient condition for life to be present there.
Answer choice (D): The journalist does not overlook the possibility that there could be unfamiliar forms of life that have evolved without the presence of liquid water. If true, this possibility would only increase the likelihood that life has evolved on Europa, with or without liquid water. Furthermore, because the journalist qualified her premise with the phrase “life as we know it,” the possibility that some other life forms do not depend on water is consistent with it.
Answer choice (E): This answer choice implies that the data transmitted by the spacecraft does not necessarily indicate the presence of liquid water, as other conditions could potentially account for such data. Although there may be room for other interpretations of the data, the factual premise on which the author depends strongly suggests that liquid water is present. Questioning the factual validity of any premise is rarely an appropriate strategy on the LSAT, and does not capture the main problem in this argument.
Flaw in the Reasoning, SN. The correct answer choice is (B)
The stimulus features conditional reasoning, which is identifiable by the use of the necessary condition indicator “only if” in the third sentence. The argument has the following structure:
LW = Liquid Water
LE = Life Evolves
Premise: LWEuropa
Premise: LE 
LW
Conclusion: LEEuropa (likely)
Note that even though the journalist qualifies her conclusion with the word “likely,” her argument is still flawed, because satisfying a condition necessary for a certain event to occur only ensures that the event can occur, not that it is likely to occur. Because the author mistakes a necessary condition for a sufficient condition, the correct answer choice will probably use at least one of these key words (or their synonyms) to describe the error in conditional reasoning. This gives savvy test takers an advantage: if you identify a stimulus with conditional reasoning and are asked a Flaw question, quickly scan the answers and identify those that contain such key words as “sufficient,” “necessary,” or both. Although this approach may not eliminate all four incorrect answers, it usually helps narrow down the number of possible contenders.
Answer choice (A): At first glance, this seems to be an attractive answer, since it does focus on the conditional aspect of this argument and uses the word “necessary,” which we expect to find in the correct answer. However, upon close inspection you should notice that this answer choice does not describe a Mistaken Reversal, but the contrapositive: if a condition is necessary for the evolution of life (liquid water), then life cannot evolve if this condition is not met (i.e. if there is no liquid water). This is a classic description of a contrapositive statement, and does not describe a Flaw in the reasoning.
Remember—although the word “necessary” makes this answer choice attractive, test makers often exploit what students perceive to be “shortcuts” and turn them into traps. To avoid falling into this one, you must prephrase and look for an answer describing a Mistaken Reversal. Although it would be acceptable to flag answer choice (A) as a contender, make sure to read all five answers before making your choice. Ultimately, only (A) and (B) contain the key words we are looking for (“sufficient,” “necessary”), and a more careful comparison between the two reveals that (B) contains the proper description of a Mistaken Reversal, whereas (A) describes a logically valid argument.
Answer choice (B): This is the correct answer choice. By confusing a necessary condition for a sufficient one, the journalist ignores the possibility that liquid water may not be the only condition necessary for the evolution of life. If other requirements need to be met before a planet can support life, then having liquid water on Europa does little to increase the likelihood that primitive life has evolved there.
Note that there are multiple ways to describe the same flaw in conditional reasoning. Compare the following examples, all of which amount to the same description of a Mistaken Reversal:
- The author treats something that is necessary for bringing about a state of affairs as something that is sufficient to bring about a state of affairs.
From the assertion that something is necessary for the evolution of life, the journalist concludes that the same thing is sufficient to ensure the evolution of life.
The journalist takes for granted that if a condition is necessary for the evolution of life, satisfying that condition alone increases the likelihood that life would evolve.
Because there are so many ways to describe a conditional reasoning flaw, it is important to prephrase an answer describing a Mistaken Reversal but keep an open mind—do not let yourself get “boxed in” by the exact language of your prephrase.
Answer choice (C): The stimulus contains no evidence suggesting that life is likely to be present on Europa if, but only if, life evolved on Europa. Both the premise and the conclusion focus on the conditions necessary (or sufficient) for life to evolve on Europa, not whether such evolution is a necessary or a sufficient condition for life to be present there.
Answer choice (D): The journalist does not overlook the possibility that there could be unfamiliar forms of life that have evolved without the presence of liquid water. If true, this possibility would only increase the likelihood that life has evolved on Europa, with or without liquid water. Furthermore, because the journalist qualified her premise with the phrase “life as we know it,” the possibility that some other life forms do not depend on water is consistent with it.
Answer choice (E): This answer choice implies that the data transmitted by the spacecraft does not necessarily indicate the presence of liquid water, as other conditions could potentially account for such data. Although there may be room for other interpretations of the data, the factual premise on which the author depends strongly suggests that liquid water is present. Questioning the factual validity of any premise is rarely an appropriate strategy on the LSAT, and does not capture the main problem in this argument.
