Solving “Necessary Assumption” Questions in the LSAT

Necessary Assumption questions require you to identify an unstated piece of information that the argument must rely on to be logically sound. In other words, if the assumption is false, the argument falls apart.

This article will help you become more confident in answering necessary assumption questions on the LSAT. You'll learn how to identify the unstated premises essential for an argument's validity. This will help you improve your ability to answer these questions and boost your overall LSAT score.

What Are "Necessary Assumption" Questions in the LSAT?

Necessary assumption questions are found in the Logical Reasoning section of the LSAT. These questions ask you to find an assumption—an unstated premise—that the argument needs to be true:

• Which one of the following is an assumption on which the scientist’s argument depends?
• The conclusion relies on which one of the following assumptions?
• The argument presupposes which one of the following?
• The university president’s argument requires the assumption that…
• The conclusion does not follow unless…

Make a Few Strong Predictions

When you're facing a necessary assumption question in the LSAT, you can often predict necessary steps that are missing from an argument before you read the question. Here’s how:

1. Find the main conclusion. If you’re having trouble, see LR: Conclusion Questions and study up on argument parts and indicators.

2. Find the premises. Don’t assume that all statements other than the main conclusion are premises. They might include an opposing viewpoint, background information, or a concession.

3. Figure out why the premises don’t prove the main conclusion. Even though you have accepted the premises as true, they still don’t prove the conclusion. Why not? What’s missing?

Focus on exactly what the argument says. Don’t assume anything that isn’t explicitly stated.

Many arguments, by the way, have more than one problem. The more problems you notice, the better prepared you are to answer the question. After you spot one or two weaknesses, you’re ready to read the answers.

How to Evaluate Answer Choices

An argument can have many necessary assumptions. Even if you predict multiple necessary assumptions, you might not predict the correct answer. Making predictions remains a key step in engaging with the argument and ensuring that you understand its logic properly.

As you read each answer choice, the only question you need to ask yourself is: “Does this answer absolutely have to be true in order for the argument to work?” If the answer to that question is yes, then that answer choice is probably correct.

What to Look For in a Necessary Assumption Question

When you're analyzing a necessary assumption question, look for an answer that you can safely say the author must agree with. In general, the weaker the answer, the better.

Be wary of answers that use all, any, each, every, only, most, and other strong words that restrict the words that follow them. (Don’t discount these words completely, though. Remember content is more important than word strength.)

More on Necessary Assumption Questions

What's the difference between a sufficient assumption question and a necessary assumption question?

A necessary assumption is a piece of information that must be true for the argument to work. If the necessary assumption is false, the argument collapses. A sufficient assumption, on the other hand, is an assumption that, if true, guarantees the conclusion. While a necessary assumption is required for the argument's validity, a sufficient assumption is just one of many possibilities that could make the argument true.

How can I avoid choosing incorrect answer choices in necessary assumption questions?

To avoid incorrect answer choices when you're answering a necessary assumption question, focus on the core argument and the relationship between the premises and the conclusion. Be wary of answer choices that are too strong or too weak. The correct answer choice will be essential to the argument's logic.

What if I can't find the necessary assumption?

If you're struggling to find the necessary assumption, try to weaken the argument. The answer choice that, when negated, weakens the argument is likely the necessary assumption. Also, consider the logical gaps in the argument and what information would be needed to bridge those gaps.