How to Solve LSAT “Sufficient Assumption” Questions

"Sufficient Assumption" questions appear in the LSAT Logical Reasoning section.

This guide will show you how to approach these questions methodically, helping you make strong predictions and land on the correct answer choice every time.

What Are "Sufficient Assumption" Questions in the LSAT?

"Sufficient Assumption" questions on the LSAT challenge you to identify an assumption that, when added to an argument, proves the conclusion.

To solve these questions, you'll need to pinpoint the argument’s main conclusion, recognize any gaps in reasoning, and find the answer choice that fills those gaps completely.

Types of "Sufficient Assumption" Questions

These bottom-up questions ask you to find an assumption (a missing premise) that, if it were true, would prove the main conclusion:

• Which one of the following, if assumed, would justify the conclusion?
• Which one of the following, if assumed, enables the argument’s conclusion to be properly drawn?
• The argument’s conclusion can be properly inferred if which one of the following is true?
• The speaker’s main conclusion logically follows if which one of the following is assumed?

To Solve Sufficient Assumption Questions, Make Your Best Prediction

A sufficient assumption is an unstated premise that’s sufficient to prove the conclusion. After you add it to the argument, you don’t need to add anything else. So ask yourself: “What would I add to this argument to fix all the problems and prove the conclusion?”

There’s often only one problem, because it’s hard to write an answer that fixes multiple problems. But if there is more than one problem, the correct answer will fix all of them. It must, or else it isn’t sufficient.

If you notice anything in the conclusion that is not mentioned in the premises, then that idea must be addressed by the correct answer.

In order to make a strong prediction, start by understanding the argument inside and out. Find the main conclusion and the premises (review here), figure out why the premises don’t prove the main conclusion, then figure out what would. If the argument is making any implicit premises, make them explicit. If the argument has a gaping hole, patch it up.

Your job is to be the emergency first-responder that’s been dispatched to save this argument.

What to Look For in the Answer Choices

As you read each answer choice, ask yourself:

1. Does this answer prove the main conclusion?
2. Does this answer completely fix every problem with the argument?

Remember, take all five answer choices as true. The correct answer will give you new evidence that proves the main conclusion by fixing all its flaws.

Because we’re trying to prove the conclusion beyond a shadow of a doubt, stronger language is usually better. Be wary of answer choices that say “some” or “many,” as those words are often not sufficient to prove the conclusion. However, content is much more important than word strength, so focus on understanding the argument.

More On LSAT “Sufficient Assumption” Questions

What is an example of a sufficient assumption?

An example of a sufficient assumption is a missing premise that, if added to the argument, guarantees the conclusion is true. For instance, if an argument concludes that "All dogs are friendly because they are pets," a sufficient assumption might be "All pets are friendly." This assumption, when included, directly connects the premises to the conclusion, making the argument logically valid.

What is the difference between Sufficient Assumption and Necessary Assumption questions?

The key difference between Sufficient and Becessary assumption questions lies in the type of assumption they ask you to identify. A sufficient assumption is one that, if true, completely guarantees the conclusion. In contrast, necessary assumptions must be true for the conclusion to hold but don’t necessarily guarantee it. In other words, a sufficient assumption proves the conclusion, while a necessary assumption is required for the conclusion to possibly be true. Here's how to answer Necessary Assumption questions.

How to spot a Sufficient Assumption question?

You can spot a Sufficient Assumption question by the phrasing in the question stem. Sufficient Assumption questions often use phrases like “Which one of the following, if assumed, would justify the conclusion?” or “Which one of the following, if assumed, enables the argument’s conclusion to be properly drawn?” These stems signal that you need to find an assumption that, when added to the premises, makes the conclusion logically valid.