Sufficient Assumption Questions
One missing piece would lock the conclusion in place. Find it.
Two tools pair with this method. The miss-pattern analyzer shows which question types cost you the most points, and the blind review worksheet gives you a second pass at every miss.
What the question asks
The question asks which answer, if true, guarantees the conclusion. The stem says something like "The conclusion follows logically if which one of the following is assumed?"
A sufficient assumption is a bridge. Add it to the evidence, and the conclusion must follow by logic alone. You are not asked what the author actually assumed. You are asked what would do the job.
Step-by-step method
- Find the conclusion and the evidence. Write each in a few words. Keep the exact terms the argument uses.
- Write the gap as an if-then. Turn the missing step into a conditional: "If [evidence], then [conclusion]." The right answer usually states this bridge outright.
- Look for strong language. Sufficient assumptions are often bold: "all," "every," "any," "whenever." Strength is a feature here, not a warning sign.
- Test the combination. Add the choice to the evidence. If the conclusion must follow and no further step is needed, the choice is sufficient.
- Do not settle for help. A choice that merely supports the conclusion is not enough. Sufficient means the conclusion is forced, not just more likely.
Worked examples
Both examples are original. They are not real LSAT questions.
Example 1
Rosa studies every evening. So Rosa will pass the bar exam.
The conclusion follows logically if which one of the following is assumed?
The answer: Everyone who studies every evening passes the bar exam.
Why: Combine the facts: Rosa studies every evening, and everyone who does so passes. The conclusion follows by logic alone. Nothing else is needed.
Example 2
The bridge was built to code, so it will withstand the storm.
Which one of the following, if assumed, allows the conclusion to be properly drawn?
The answer: Any bridge built to code will withstand a storm of this size.
Why: This bridge was built to code. Anything built to code withstands this storm. Therefore this bridge withstands it. The bridge premise is complete.
Do not fear strong answers here
Sufficient assumption is the one question type where strong language is a good sign. The right answer must be enough, on its own, to make the conclusion follow. That is a demanding job. The choices that do it usually sound bold: "all," "always," "whenever." Students trained to distrust strong language on other question types talk themselves out of the right answer here. On this type, bold is often correct.
The test is simple once you see it. Add the answer choice to the premises, then ask: does the conclusion now follow with no gaps? If you still need one more unstated step, the choice is not sufficient. A choice that gets you 90 percent of the way is wrong. Sufficient means the whole way.
The most common trap is a choice that bridges the wrong gap. It connects two terms that appear in the argument, but not the two terms the conclusion needs connected. Map the conclusion first: what new term does it introduce that the premises never mention? The right answer almost always supplies exactly that missing link.
Common traps
- A choice that is necessary but not sufficient. It helps, but the conclusion still does not follow for sure.
- A choice that adds an irrelevant fact. Extra truth is not a bridge.
- A choice that only makes the conclusion more likely. "Most" and "usually" rarely suffice.
- A choice that bridges the wrong gap. Match the exact terms of the conclusion.
Practice the method
The free diagnostic scores every LR question type and shows exactly where you are losing points.