This is a continuation of the Simple Guide on Necessary Assumption Questions. I encourage you to take a look if you haven’t; the explanation of the negation test with examples is very useful. Lots of students start out confused by Necessary Assumption (NA) questions and hit a groove after familiarizing themselves with the negation test. This alone can get you far, but for a student aiming for perfection, there is a bit more you want to know. In this guide, I will outline a few ways NA questions tend to trip students up and how to avoid falling for them.
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NA questions can be difficult for a variety of reasons. There are subtle gaps in reasoning that we have to identify and ambiguous answer choices (ACs) that force us to decide if a sufficient assumption can be right. Advanced students typically have the most trouble with conditional logic in the ACs, as the negation test fails us there.
One thing that tripped me up while studying was the dense, abstract stimuli; the ones you read once and shake your head and start over. In some other question types, we can get away with a partial understanding. With NA questions, it’s often difficult to do so.
When confused, people often select the most clear, strongly worded ACs, which tend to be incorrect by design. To combat this, I recommend asking “why?” after each statement. By this, I specifically mean asking “What evidence did the author provide for that?”. Use this to follow the chain of logic and identify the assumptions.
Simple example: “Bob, a friend, is a good mechanic. I just bought a car and it's making weird noises. If I am smart, I’m probably going to owe Bob a lot of money.”
Think about how many potential necessary assumptions there are:
Follow along with the reasoning on these:
This is pretty standard advice, but I still see advanced students make this mistake. Typically, the weaker the language, the easier it is for a statement to be necessary. However, the correct AC can range from minor and inconsequential to the argument (but must be true nonetheless) to an assumption guaranteeing the truth of the conclusion (P→C). From the above example, a very weak NA could be “Bob is not in a coma” or something dumb like that.
The more common mistake is ignoring those weak ACs in favor of something too strong to be absolutely necessary. However, some advanced students are wary of this and excessively avoid strong language. Strong language can be correct if the stimulus support is there; do not take strong language to be disqualifying.
Try out these. The first is a well-known question where the correct and trap AC are selected at the same rate:
I’m including these simpler concepts because I have too many students who learn them for the first time well into the 170s.
1) The negation test does not reveal new information for conditional ACs.
2) If the main conclusion is a conditional like the question above, the correct AC is not going to merely confirm the existence of the sufficient condition.
The first point in the previous section prompts the obvious question: how should we solve questions with conditional ACs?
1) Consider what its role in the argument would be. Is it filling a gap between a premise and a conclusion? If it simply connects p→c, it can feel too strong but be required.
2) Some are also just easy. The conclusion will look like “If I go to school, then I will go to math class.”
3) One claim I see confusing students is that the correct AC, if negated, should guarantee that it is impossible for the conclusion to be factually true. It actually only has to “make the argument fall apart” by showing that the conclusion does not follow; an important distinction.
4) In the same vein, I hear too often that students did not select the correct AC because “it was a sufficient assumption”. This does not disqualify it from being correct.
Thus, when we see a conditional as an AC, we try to plug it back into the argument and see if it is necessary for validity.
This is not intended to be a mock LSAT question with a correct AC; it is a task to practice the skills discussed previously.
Determine if each AC works as an NA, SA, both, or neither.
The physiological limits of basketball players today are largely unchanged from decades past. Consequently, regardless of increased youth pipelines, modern diets, and trainers, NBA players' ability to pull off new great feats of athleticism has stagnated. Thus, if future breakthroughs in genetic engineering or biopharmaceutical science expand the physiological limits of athletes, this plateau will be broken.
a) NBA players today would be able to pull off new great feats of athleticism only if significant physiological changes occurred.
b) If genetic engineering and biopharmaceutical breakthroughs expand the physiological limits of athletes, NBA players will be able to pull off new great feats of athleticism.
c) Genetic engineering or biopharmaceutical sciences will eventually be able to expand the physiological limits of athletes.
d) If NBA athletes pull off new great feats of athleticism, it will be due to genetic engineering or biopharmaceutical science.
Choice A)
Is it necessary?
Is it sufficient?
Choice B)
Is it necessary?
Is it sufficient?
Choice C)
Is it necessary?
Is it sufficient?
Choice D)
Is it necessary?
Is it sufficient?
A: NA
B: SA
C: Neither
D: Neither
