#6 - Assumption, Subject Perspective

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=14432)

The correct answer choice is (E)

Although assumption questions are far more common in Logical Reasoning than in Reading
Comprehension, our approach will be the same. The answer you select must contain a statement
upon which Bull and Brandon’s argument depends, i.e. a statement that is necessary for their
conclusion to be true.

In lines 50-58, Bull and Brandon argue that lichenometry requires careful site selection and accurate
calibration of lichen growth, concluding that their method is “best used for earthquakes that occurred
within the last 500 years” (line 53-54). The rest of the paragraph provides additional information
regarding the specific environmental conditions that must be avoided or “factored into” the
calibration of lichen growth rates. This assumes, of course, that seismologists can properly factor in
the effect of these conditions when calibrating lichen growth rates.

Answer choice (A): Although this answer choice supports the position that lichenometry produces
more accurate results than radiocarbon dating, this is not an assumption upon which Bull and
Brandon’s argument depends. To double-check if this is an assumption, simply apply the Assumption
Negation Technique as if it were a Logical Reasoning question—logically negate the answer and ask
yourself if the following statement would undermine their argument:

• Lichenometry is just as accurate as other methods for dating earthquakes that
  occurred within the past 500 years.

Bull and Brandon merely stated that lichenometry is best used for dating such earthquakes that
occurred within the last 500 years, not that it is the absolute best method for dating such earthquakes.
Since the logical opposite of Answer choice (A) does not weaken Bull and Brandon’s conclusion,
this answer choice does not contain an assumption upon which their argument depends.

Answer choice (B): The statements made by Bull and Brandon concern lichenometry, not
radiocarbon dating, which is sufficient to eliminate this answer choice from consideration. If you are
having trouble with this answer choice, apply the Assumption Negation Technique:

• There is a reliable method for detecting the intensity of the radiation now hitting
  Earth’s upper atmosphere.

Even if there were a reliable method for determining the intensity of the radiation now hitting Earth’s upper atmosphere, this would not help us overcome the problem of fluctuating radiation during the
past 300 years. Since this fluctuation is the reason why radiocarbon datings of events during this
period are of little value (lines 45-48), it is still possible that lichenometry is more accurate than
radiocarbon measurements for dating such events.

Answer choice (C): Hopefully, you were able to eliminate this answer choice relatively quickly. The
types of rocks where lichens can grow are irrelevant to the statements made by Bull and Brandon in
the third paragraph.

Answer choice (D): If the mountain ranges that produce the kinds of rockfalls studied in
lichenometry are also subject to more frequent snowfalls and avalanches, it may prove difficult to
minimize the effect of various disturbances affecting normal lichen growth. This would undermine
the feasibility of calibrating lichen growth rates at these sites, and weaken the argument that
lichenometry is more accurate than radiocarbon dating. Since the question does not ask us to weaken
Bull and Brandon’s statements, this answer choice is incorrect.

Answer choice (E): This is the correct answer, as it agrees with our prephrase of a Defender
Assumption. If this answer is troubling you, use the Assumption Negation Technique and ask
yourself if the following statement would undermine Bull and Brandon’s argument:

• The extent to which conditions like shade and wind have affected the growth of
  existing lichen colonies cannot be determined.

If the effect of environmental conditions affecting lichen growth cannot be determined, it would be
difficult to factor them into our calibration of lichen growth rates. As a result, lichenometry may
prove unreliable in dating past earthquakes, which would weaken Bull and Brandon’s argument.

[mahmed19]

Hello!

I am still having some trouble understanding why A is incorrect. When I did the logical negation of the answer choice, I got:

While lichenometry is the (not necessarily less accurate) when it is used to date earthquakes that occurred more than 500 years ago, it is (not necessarily more) accurate than other methods for dating such earthquakes.

I chose this answer because I thought it undermined the argument, but is there a component that I am missing? Thank you in advance.

- Maliha

[Rachael Wilkenfeld]

Hi Mahmed,

First, be careful with those negations! You don't want to negate in multiple places because it changes the meaning of the phrase. You want to negate typically the main verb in the main clause, but not the dependent clauses. For example. let's look at some possible negations of the statement "While not all the press coverage was positive, overall Cruel Summer was a hit!"

Possibility 1: "While all the press coverage was positive, Cruel Summer was a hit." This doesn't negate the main part of the phrase, and isn't the opposite idea.

Possibility 2: While all the press coverage was positive, Cruel Summer was not a hit." This is a different situation than our original. Because we negated both, we both changed the situation (the press coverage) and the response to that coverage. It's a different negation.

Possibility 3: "While not all the press coverage was positive, overall Cruel Summer was not a hit." This is the logical opposite of our original statement.

So with answer choice (A), we'd negate it to "while lichenometry is less accurate when it is used to date earthquakes that occurred more than 500 years ago, it is no more accurate than other methods for dating such earthquakes." We negate that main verb.

In this case, that has no bearing on the argument. We don't really need to know the accuracy of lichenometry on earthquakes more than 500 years old. The arguments in the passage are all about using it for more recent earthquakes.

Hope that helps!

[mahmed19]

Hi Rachael,

Thank you for your response, I just finished reading this section in the Logical Reasoning Bible, but I am having some trouble grasping the concept still. Are there any other resources for this negation technique? Thank you in advance.

- Maliha

[Robert Carroll]

Maliha,

The blog posts here are relevant:

https://blog.powerscore.com/lsat/logica ... -sentence/

https://blog.powerscore.com/lsat/negati ... tatements/

https://blog.powerscore.com/lsat/bid-29 ... -the-lsat/

Also realize that in many of the threads for Assumption questions on the forum, the Assumption Negation technique will be used (often in our explanations!), so looking around at those threads can provide specific examples of negations at work.

Robert Carroll

[mahmed19]

Thank you Robert!

- Maliha