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- Wed Mar 30, 2016 6:44 pm
#22665
Question #9: Parallel Flaw. The correct answer choice is (E)
This is an interesting Parallel Flaw question, as much for what we’re told in the stimulus as for how the question is posed.
The stimulus presents a fairly straightforward, albeit highly dubious, argument: if life ever existed on the Moon it would have left evidence, so since all lunar excursions have failed to find that evidence there must never have been life on the Moon.
Structurally speaking that’s easy: two premises and a concluding final sentence. But can you see the faulty reasoning? It’s the old mistake of thinking that absence of evidence is evidence of absence! Or more explicitly that just because no signs of life have been found so far, even if they are to be expected, it doesn’t prove that those signs aren’t there and still waiting for discovery. Life could, therefore, have existed and left signs, and we just haven’t spotted them yet.
So what’s interesting about the question itself? We’re not told that flawed reasoning is present, despite the fact that it clearly is. If you’ll recall, for years and years (beginning back in 1991 and lasting for decades) the test makers would indicate the presence of a reasoning error when they presented the Parallel question stem: “The flawed pattern of reasoning in the argument above is most similar to that in which one of the following?” (or similar). But here we’re left to recognize the mistake on our own! This happens on occasion, albeit rarely, so no longer can you just assume that LSAC will always indicate that a flaw is present. When they do, great! But when they don’t you still need to consider the argument’s validity, and if invalid you must incorporate the mistake into your answer choice analysis since the correct answer will commit the same error.
In this case we need an argument in an answer choice that matches the mistake in the stimulus: we looked for evidence of something and didn’t find it, so that something doesn’t exist.
Answer choice (A): This choice never presents the idea of looking for something and not finding it, and then drawing a definitive conclusion from that absence. It’s a poor argument, sure, but for an entirely different reason than what we read above.
Answer choice (B): Note a key thing about this wrong answer: it uses language of probability. “It is unlikely that...” The conclusion in the stimulus is absolute, so right away you can dismiss this choice. (It’s wrong for other reasons as well, like the “almost empty” idea in a premise, but in Parallel a single misstep is sufficient for removal)
Answer choice (C): is similar to (B) in its use of likelihood in the conclusion. Arguing that “voters will probably go with Hendricks” is quite different than arguing “there has never been life on the Moon.”
Answer choice (D): is the best option so far, in that it at least describes the search for evidence and uses absolute language in doing so. However it tells us that the evidence sought was actually found—signs of rodents in the warehouses were observed—so it is in effect the opposite of what the stimulus provides and thereby incorrect.
A sidenote for anyone curious as to (D)’s logical validity: it too is a poor argument, albeit for different reasons than the stimulus. The stimulus creates a near-conditional relationship between life and signs of life, and then attempts to conclude the contrapositive (no signs --> no life). The problem is that “no signs” is never satisfactorily proven (no signs found is not the same as no signs present). (D) on the other hand is a Mistaken Reversal: rodents responsible tells you signs, which the author turns into signs telling you rodents responsible. A bad argument to be sure, but a different kind of error than that in the stimulus.
Answer choice (E): This is the correct answer choice. And here we have it. An army attack would show signs of either troop movement or a weapons transfer, and the people looking for such things (those reporting intelligence) haven’t observed them happening. Hence, they must not be happening and no attack is planned. The same logical hole exists, where failing to observe something doesn’t prove its nonexistence.
This is an interesting Parallel Flaw question, as much for what we’re told in the stimulus as for how the question is posed.
The stimulus presents a fairly straightforward, albeit highly dubious, argument: if life ever existed on the Moon it would have left evidence, so since all lunar excursions have failed to find that evidence there must never have been life on the Moon.
Structurally speaking that’s easy: two premises and a concluding final sentence. But can you see the faulty reasoning? It’s the old mistake of thinking that absence of evidence is evidence of absence! Or more explicitly that just because no signs of life have been found so far, even if they are to be expected, it doesn’t prove that those signs aren’t there and still waiting for discovery. Life could, therefore, have existed and left signs, and we just haven’t spotted them yet.
So what’s interesting about the question itself? We’re not told that flawed reasoning is present, despite the fact that it clearly is. If you’ll recall, for years and years (beginning back in 1991 and lasting for decades) the test makers would indicate the presence of a reasoning error when they presented the Parallel question stem: “The flawed pattern of reasoning in the argument above is most similar to that in which one of the following?” (or similar). But here we’re left to recognize the mistake on our own! This happens on occasion, albeit rarely, so no longer can you just assume that LSAC will always indicate that a flaw is present. When they do, great! But when they don’t you still need to consider the argument’s validity, and if invalid you must incorporate the mistake into your answer choice analysis since the correct answer will commit the same error.
In this case we need an argument in an answer choice that matches the mistake in the stimulus: we looked for evidence of something and didn’t find it, so that something doesn’t exist.
Answer choice (A): This choice never presents the idea of looking for something and not finding it, and then drawing a definitive conclusion from that absence. It’s a poor argument, sure, but for an entirely different reason than what we read above.
Answer choice (B): Note a key thing about this wrong answer: it uses language of probability. “It is unlikely that...” The conclusion in the stimulus is absolute, so right away you can dismiss this choice. (It’s wrong for other reasons as well, like the “almost empty” idea in a premise, but in Parallel a single misstep is sufficient for removal)
Answer choice (C): is similar to (B) in its use of likelihood in the conclusion. Arguing that “voters will probably go with Hendricks” is quite different than arguing “there has never been life on the Moon.”
Answer choice (D): is the best option so far, in that it at least describes the search for evidence and uses absolute language in doing so. However it tells us that the evidence sought was actually found—signs of rodents in the warehouses were observed—so it is in effect the opposite of what the stimulus provides and thereby incorrect.
A sidenote for anyone curious as to (D)’s logical validity: it too is a poor argument, albeit for different reasons than the stimulus. The stimulus creates a near-conditional relationship between life and signs of life, and then attempts to conclude the contrapositive (no signs --> no life). The problem is that “no signs” is never satisfactorily proven (no signs found is not the same as no signs present). (D) on the other hand is a Mistaken Reversal: rodents responsible tells you signs, which the author turns into signs telling you rodents responsible. A bad argument to be sure, but a different kind of error than that in the stimulus.
Answer choice (E): This is the correct answer choice. And here we have it. An army attack would show signs of either troop movement or a weapons transfer, and the people looking for such things (those reporting intelligence) haven’t observed them happening. Hence, they must not be happening and no attack is planned. The same logical hole exists, where failing to observe something doesn’t prove its nonexistence.
T because we know that the spy we are referring to is also a traitor, they are one and the same. So, if we catch the spy, we catch the traitor. If spy, then traitor. Knowing that the person is a spy is sufficient to know they are a traitor. It is necessarily true that the person is a traitor, if we know they are a spy. 