This blog is a part of the “Approach Question Type” series and like all articles in this series will focus on step 4 of the “Analyze Stimulus” step. If you need a refresher on how to approach LR questions generally, make sure to check up on our blog "How to Approach the Logical Reasoning Section.”
Table of Contents:
NA questions require you to identify an assumption that must be true for the argument to be valid. If this assumption is not true, the argument falls apart. The method to find the correct answer is to understand how to make the argument completely fall apart.
NA questions are not the same as Sufficient Assumption (SA) questions — think of them as very distant cousins. Besides depending on your ability to understand and parse through assumptions in an argument, NA and SA questions have little in common so be sure not to confuse the two.
In contrast, sufficient assumption questions require you to identify an assumption that, if true, guarantees the conclusion. The assumption is strong enough that it makes the argument valid on its own. To read more about SA questions, check out our guide here.
A Necessary Assumption has a logical flow of two options like this:
Take special note that a Necessary Assumption being fulfilled does not prove the validity of the argument. A Necessary Assumption is always a part of the core structure of the argument; without it, the argument collapses. This may make it seem like a strengthener for the argument, which in a way is true. However, Necessary Assumptions are crucial for the argument's validity, acting as a “bare minimum” before we can even attempt to engage with the conclusion. Strengtheners in the LR section enhance the argument's persuasiveness but are not indispensable.
There are three crucial concepts of which you should familiarize yourself with to improve your NA skills.
Identify the Argument: Understand the argument's conclusion and the evidence provided to support that conclusion. Accept the statements and the argument as true.
Prediction Practice Drill: Determine some possible NA’s — what must be true for the argument to work before looking at the answer choices. In practice, you can make infinite amounts of assumptions that must be true, any of which or none of which may appear in the answer choice options. Your goal here is not to actually predict the answer choice option, though it would be nice if your prediction did show up.
The practice here is to get in the mind of thinking how to absolutely nullify an argument. Necessary requirements to arguments must be satisfied, and in many arguments, these requirements are indeed assumed. There can be necessary assumptions pulled out in every sentence, some are so obvious we don’t need to mention. For example, if we are told that Michael is a strong law school applicant, a reasonable assumption that all of us likely agree on is that Michael is not a dog (as far as I know, dogs cannot be lawyers!). Sure, maybe you didn’t think of that initially, but it is indeed necessary.
Use this prediction practice drill as a starting point; it’s okay to point out even the most obvious, “of course!” assumptions, because sometimes the LSAT will have even these types of assumptions laid out in the answer choices. Eventually you want to be able to parse through more obscure, nuanced NA’s, but NA’s can be very bare minimum, so be sure to not overlook the basic “obvious” ones.
Negation Test for Answer Choices: One way to confirm you've identified the correct necessary assumption is to use the negation test. The negation test helps determine whether a statement is a necessary assumption by checking if negating (i.e., denying) the statement would invalidate the argument. If negating the statement causes the argument to fall apart, then the statement is a necessary assumption.
If we didn’t assume that Michael is not a dog earlier, negating this statement would mean Michael is a dog. That would make the argument he is a strong law school applicant impossible!
