Tuesday, December 17, 2013

LSAT Logical Reasoning: Assumption

Question Type: Assumption
Assumption questions ask you to identify the missing link in the logic of the stimulus
argument.
Some example question stems are
1. Which one of the following, if assumed, allows the argument’s conclusion to be
properly drawn?
2. Which one of the following is an assumption on which the argument depends?
3. The final conclusion above follows logically if which one of the following is
assumed?
4. The claim made by the official in the argument above depends on the presupposition
that
5. Which one of the following is an assumption on which the argument relies?
Strategies
The most time-efficient way to answer assumption questions is to recognize the missing
link in the argument as you read the stimulus. Sometimes, the wording of the argument
and the answer choices can be confusing. So, you might want to employ the technique
of negating the answer choices that you want to test. Negation is fully explained in
Chapter 3, “Introduction to LSAT Logic.”
Because an assumption is an unstated piece of evidence, this technique “knocks out”
each answer choice that you test, one by one. When you test the correct answer, you are
knocking out a piece of evidence, and the argument should suffer accordingly.
In tutoring sessions, we often use the analogy of testing to see if a wall within a house
or an office is important to the structure by knocking the wall down to see if the roof
falls in. If the roof falls in, we have shown that the wall was important. If there is no
effect on the structure, the wall was not a load-bearing wall. In other words, the wall
was irrelevant to the strength of the structure.
Sample Assumption Question
Consider the following example:



1. The birth rate in Country X is down this year by 12% compared to last year. The
death rate in Country X has remained stable for several years. Therefore, the
population of Country X is decreasing measurably.
Which of the following is assumed by the author of the argument above?
(A) The causes of the declining birthrate in Country X can be discovered
through physician surveys.
(B) Statisticians are able to predict future changes in the size of the population
of Country X.
(C) Country Y, which has a nearly identical population to Country X, is experiencing
the same population shift as Country X.
(D) There was no significant migration into Country X during the time under
discussion.
(E) The causes of the declining birthrate in Country X are primarily economic
in nature.
 
The best answer is D. You might be able to answer the question directly by simply recognizing
the missing piece of evidence and selecting it. However, if you aren’t able to do so,
you can still determine the correct answer by negating whichever answer choices you view
as potentially correct. It is not likely that you will have time to carefully negate each choice
presented. So, you will need to “filter out” choices that you find clearly irrelevant.
Let’s say that you could easily recognize that answer choice C is irrelevant since it
discusses Country Y and, therefore, it can’t possibly be the missing link between the
stated evidence and the stated conclusion, which both involve Country X. Likewise, let’s
say that you could eliminate answer choice B, which is about predicting the future,
whereas the stimulus argument is about the recent past.
That leaves answer choices A, D, and E still in contention. Try to negate answer choice
A. You should come up with something like: “The causes of the declining birthrate in
Country X cannot be discovered through physician surveys.” Since physicians play no
part in the stimulus argument, you should recognize that neither the original phrasing
of answer choice A, nor its negation, has any bearing on the relationship between the
evidence and the conclusion stated in the argument. Similarly, negating E with “The
causes of the declining birthrate in Country X are not primarily economic in nature,”
has no impact on the likelihood that the conclusion is valid. However, if you negate
answer choice D, you get “There was significant migration into Country X during the
time under discussion.” This would dramatically call into question the stated conclusion
that the population of Country X is declining measurably. Therefore, answer choice D
must be correct.

No comments:

Post a Comment