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#40957
Complete Question Explanation
Justify the Conclusion, SN. The correct answer choice is (D)
This is a very challenging question, and possibly one of the most difficult logical reasoning questions on the test, in part because of the convoluted conditional approach taken by the author.
The stimulus begins with the author’s conclusion that we will not be able to determine the presence of sentient beings outside our solar system unless some of them are at least as smart as humans. Although the stimulus begins with the familiar term “if,” the first sentence could be more simply restructured as follows:
Even though there are no conclusion indicators to help us identify the conclusion, note that the second sentence contains two premises that support the observation in the first sentence: first, we will not be able to send spacecraft outside our solar system in the near future, and second, any sentient being able to communicate with us would need to be at least as intelligent as we are.
In other words, if we want to determine whether sentient beings exist outside our solar system, one approach might be to send a spacecraft. Without spacecraft as an option, however, the author asserts that we would have to rely on these beings’ ability to communicate with us. This, in turn, would require that such sentient beings be at least as intelligent as humans. The relationship between premises and conclusion is implicitly conditional, and, when re-worded, can be diagrammed as follows:
The question stem asks us to identify a statement that, if assumed, would enable to the conclusion to be properly drawn. Despite the word “assumed” in the stem, this is a Justify question because our job is not to identify a statement upon which the argument depends, but rather to prove the conclusion by adding a piece of information to the premises. The sufficient condition indicator (“if”) in the question stem is a reminder that you must select an answer that is sufficient to prove the conclusion by using the Justify Formula:
Premises + Answer choice = Conclusion
As with most Justify questions, there is a logical gap between the premises and the conclusion. To prove the conclusion, we must establish that there are only two ways to determine the existence of sentient begins outside our solar system: either we send a spacecraft outside our solar system, or the sentient themselves must be able to communicate with us. That way, if one of the two options is ruled out, the only other way to determine the existence of sentient beings would be to pursue the other option:
Note that the relationship between the two options contains a negative sufficient condition—if one cannot occur, the other must occur. The contrapositive would serve the same function: if the sentient beings cannot communicate with us, then the only other option for determining their existence would be to send a spacecraft to its planet:
Another way to approach this Justify question would be as follows:
Answer choice (A): Because the conclusion focuses on whether sentient beings exist outside our solar system, the fact that they do not exist on planets inside our solar system is irrelevant. Even if there were no sentient beings on planets in our solar system, that alone does not prove that there are only two ways of determining their existence.
A savvy test taker would eliminate this answer choice immediately because it does not contain the element of “Send Spacecraft.” Since this element appears in the premises but not in the conclusion, we would expect it to appear in the correct answer.
Answer choice (B): Even if the sentient beings would want to communicate with us, that does not prove that we would have to rely on their ability to communicate with us. Because the possibility remains that there is a third way to determine their existence, the conclusion is not fully justified.
To some test takers, this may seem like an assumption answer (which would still make it incorrect, as we are not answering an Assumption question). However, applying the Assumption Negation technique reveals that this is not an assumption: even if the sentient beings did not want to communicate with us, that would not weaken the conclusion that determining their existence requires that these beings be at least as intelligent as we are. Granted, if they refused to communicate with us, our job of determining their existence would be made considerably more difficult, but this is irrelevant to the conclusion of the argument. Therefore, answer choice (B) is neither sufficient, nor necessary, for the conclusion to be true.
Answer choice (C): Since the author already established that sending a spacecraft to planets outside our solar system is impossible in the near future, this answer choice merely restates a premise in the argument. If you found this answer choice attractive, you probably mistook the Justify question stem for a Must Be True question stem.
Answer choice (D): This is the correct answer choice, as it is the contrapositive of the Justify
Formula:
In other words, without the option of sending a spacecraft outside out solar system, the only other way to determine the existence of sentient beings is for them to communicate with us. Since their ability to communicate with us requires intelligence, it logically follows that determining the existence of sentient beings outside our solar system requires that such beings be at least as intelligent as humans.
Note that the Justify Formula could have been phrased in a number of ways:
A smart test taker would eliminate this answer choice immediately because it does not contain the element of “Send Spacecraft.” Since this element appeared in the premises but not in the conclusion, we would expect it to appear in the correct answer.
Justify the Conclusion, SN. The correct answer choice is (D)
This is a very challenging question, and possibly one of the most difficult logical reasoning questions on the test, in part because of the convoluted conditional approach taken by the author.
The stimulus begins with the author’s conclusion that we will not be able to determine the presence of sentient beings outside our solar system unless some of them are at least as smart as humans. Although the stimulus begins with the familiar term “if,” the first sentence could be more simply restructured as follows:
- We will not be able to determine the existence of other sentient beings (even if they do actually exist) unless some of them are at least as intelligent as humans.
Even though there are no conclusion indicators to help us identify the conclusion, note that the second sentence contains two premises that support the observation in the first sentence: first, we will not be able to send spacecraft outside our solar system in the near future, and second, any sentient being able to communicate with us would need to be at least as intelligent as we are.
In other words, if we want to determine whether sentient beings exist outside our solar system, one approach might be to send a spacecraft. Without spacecraft as an option, however, the author asserts that we would have to rely on these beings’ ability to communicate with us. This, in turn, would require that such sentient beings be at least as intelligent as humans. The relationship between premises and conclusion is implicitly conditional, and, when re-worded, can be diagrammed as follows:
The question stem asks us to identify a statement that, if assumed, would enable to the conclusion to be properly drawn. Despite the word “assumed” in the stem, this is a Justify question because our job is not to identify a statement upon which the argument depends, but rather to prove the conclusion by adding a piece of information to the premises. The sufficient condition indicator (“if”) in the question stem is a reminder that you must select an answer that is sufficient to prove the conclusion by using the Justify Formula:
Premises + Answer choice = ConclusionAs with most Justify questions, there is a logical gap between the premises and the conclusion. To prove the conclusion, we must establish that there are only two ways to determine the existence of sentient begins outside our solar system: either we send a spacecraft outside our solar system, or the sentient themselves must be able to communicate with us. That way, if one of the two options is ruled out, the only other way to determine the existence of sentient beings would be to pursue the other option:
Note that the relationship between the two options contains a negative sufficient condition—if one cannot occur, the other must occur. The contrapositive would serve the same function: if the sentient beings cannot communicate with us, then the only other option for determining their existence would be to send a spacecraft to its planet:
Another way to approach this Justify question would be as follows:
- (1) Elements that appear in the premises but not the conclusion usually appear in the correct answer. Although these premise elements do not have to appear in the correct answer, they often do because they represent a convenient linking point. In this argument, “Send Spacecraft” appears in the premises but not in the conclusion. Therefore, it is highly likely that it would appear in the correct answer. Its absence from answer choices (A), (B), and (E) helps eliminate them.
(2) Elements that are common to the conclusion and at least one premise normally do not appear in the correct answer, because there is a bridge already established that justifies the presence of that element in the conclusion. Here, the element of “Determine Exist” is common to both the premises and the conclusion and need not be present in the correct answer. Its presence in answer choices (B), (C), and (E) helps eliminate them.
Answer choice (A): Because the conclusion focuses on whether sentient beings exist outside our solar system, the fact that they do not exist on planets inside our solar system is irrelevant. Even if there were no sentient beings on planets in our solar system, that alone does not prove that there are only two ways of determining their existence.
A savvy test taker would eliminate this answer choice immediately because it does not contain the element of “Send Spacecraft.” Since this element appears in the premises but not in the conclusion, we would expect it to appear in the correct answer.
Answer choice (B): Even if the sentient beings would want to communicate with us, that does not prove that we would have to rely on their ability to communicate with us. Because the possibility remains that there is a third way to determine their existence, the conclusion is not fully justified.
To some test takers, this may seem like an assumption answer (which would still make it incorrect, as we are not answering an Assumption question). However, applying the Assumption Negation technique reveals that this is not an assumption: even if the sentient beings did not want to communicate with us, that would not weaken the conclusion that determining their existence requires that these beings be at least as intelligent as we are. Granted, if they refused to communicate with us, our job of determining their existence would be made considerably more difficult, but this is irrelevant to the conclusion of the argument. Therefore, answer choice (B) is neither sufficient, nor necessary, for the conclusion to be true.
Answer choice (C): Since the author already established that sending a spacecraft to planets outside our solar system is impossible in the near future, this answer choice merely restates a premise in the argument. If you found this answer choice attractive, you probably mistook the Justify question stem for a Must Be True question stem.
Answer choice (D): This is the correct answer choice, as it is the contrapositive of the Justify
Formula:
In other words, without the option of sending a spacecraft outside out solar system, the only other way to determine the existence of sentient beings is for them to communicate with us. Since their ability to communicate with us requires intelligence, it logically follows that determining the existence of sentient beings outside our solar system requires that such beings be at least as intelligent as humans.
Note that the Justify Formula could have been phrased in a number of ways:
- If we cannot send a spacecraft outside our solar system in an effort to determine the existence of sentient beings, we must rely on these beings’ ability to communicate with us.
To determine if there are sentient beings on other planets outside our solar system, we must either send a spacecraft there, or the sentient beings themselves must be able to communicate with us.
A smart test taker would eliminate this answer choice immediately because it does not contain the element of “Send Spacecraft.” Since this element appeared in the premises but not in the conclusion, we would expect it to appear in the correct answer.
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