Sufficient/Necessary

On the LSAT, you must be able to identify any assumptions, or gaps, between the evidence and the conclusion. There are two types of Assumptions: Sufficient Assumptions and Necessary Assumptions. These questions typically ask you to identify the flaw and fix it. So, these are often like Strengthening/Weakening questions we just discussed.

CHALLENGE: Identify the Necessary/Sufficient Assumptions

Necessary Assumption questions have stems phrased in the following ways:

• The argument requires/depends on/relies on the assumption that
• Which of the following is an assumption on which the argument relies/depends?
• Which one of the following is an assumption the argument requires?
• The argument requires/depends on/relies on assuming which one of the following?

Sufficient Assumption questions are phrased like this:

• The conclusion follows logically if which one of the following is assumed?
• The conclusion of the argument can be properly drawn if which one of the following is assumed?

Notice that Necessary Assumption questions always contain a word that means “necessary” or “required”, while Sufficient Assumption questions ask for a guarantee that the conclusion will be reached.

How to solve

1. Identify the premises and the conclusion: The answer is the conclusion.
2. Avoid trap choices: Perhaps more than any question type, Main Idea questions have the most devious trap answer choices.
   a) Avoid answer choices that are true, but aren’t the Main Idea.
   b) Don’t pick a premise of the argument.