Is it important to know the difference between necessary and sufficient assumptions?

Yes, you will quickly come to notice how easily they can be confused when evaluating arguments. Many wrong answer choices will include a switch up of sufficient and necessary assumptions (ie. you are looking for a necessary assumption and a wrong choice gives you a sufficient assumption, or vice vera). I personally recommend spending some time developing your understanding of the differences between them, and their individual roles in arguments - I definitely noticed an increase in my ability to identify both necessary and sufficient assumptions once I was able to explain the difference between them.

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Course: LSAT > Unit 1

Lesson 6: Logical Reasoning – Articles

Sufficient assumptions | Quick guide

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A quick guide to approaching questions that ask you to identify a sufficient assumption

This question asks you to identify a sufficient assumption—that is, an assumption that, if added to the argument, would make it logically valid. We’re looking for something that would fix all of an argument’s problems, bridging the gap between what the support justifies and what the conclusion claims.

Look out for common wrong choice types:

Not enough: Statements that do help, but not enough to guarantee the conclusion following from its support.
Necessary assumptions: Assumptions that are necessary but not sufficient to guarantee the result.
Not relevant: Information that’s outside of the argument's scope, and thus unable to connect the support to its conclusion.
Backwards: A statement that establishes, "Because [passage's conclusion], therefore [passage's evidence]." Example: My fish is swimming, so my fish must be alive. A backwards choice would say something like, "All beings that are alive must be swimming" instead of, "All beings that are swimming must be alive."

It’s best to make a prediction on Sufficient Assumption questions, to save time in the choices and make the tempting choices look less tempting.

✓ Identify the conclusion and support. Make sure to separate the conclusion from the support—this will make the gap in the argument more visible to you. It can also be helpful to phrase the argument’s structure to yourself as, “The arguer believes [conclusion], because [support]” in order to detect any leaps in logic or scope.

✓ Identify any gaps in the argument. Is there a gap in scope between the support and the conclusion? Does the topic shift in a meaningful way? If so, then connecting the topic in the support and the topic in the conclusion in the correct logical relationship will allow the conclusion to follow from its support.

✓ Diagram if necessary. Is there conditional logic in the argument? If so, it can be very helpful to diagram that logic.

✓ Match a choice to your prediction. Once you’ve made a prediction of the sufficient assumption, find the choice that matches your prediction.

✓ Eliminate strategically. If you weren’t able to make a prediction, look to eliminate choices by testing them against your knowledge of common wrong choices—which choices aren’t even relevant to the argument? Do any of them move from the conclusion to the evidence, instead of from the evidence to the conclusion?

✓ Test by affirming unless you are crunched for time. Test the choice you chose by affirming: when you “add” your choice to the passage’s original support, it should create an ironclad journey from the support to the passage’s conclusion.

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Marissa Weil
Posted 4 years ago. Direct link to Marissa Weil's post “Is it important to know t...”
Is it important to know the difference between necessary and sufficient assumptions?
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- Megan Sargent
  Posted 4 years ago. Direct link to Megan Sargent's post “Yes, you will quickly com...”
  Yes, you will quickly come to notice how easily they can be confused when evaluating arguments. Many wrong answer choices will include a switch up of sufficient and necessary assumptions (ie. you are looking for a necessary assumption and a wrong choice gives you a sufficient assumption, or vice vera). I personally recommend spending some time developing your understanding of the differences between them, and their individual roles in arguments - I definitely noticed an increase in my ability to identify both necessary and sufficient assumptions once I was able to explain the difference between them.
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  (19 votes)