**QUESTION TEXT:** Selena claims to have psychic powers. So if we…

**QUESTION TYPE:** Sufficient Assumption

**CONCLUSION:** If we find out whether Selena is correct, we’ll find out if psychic powers are possible.

**REASONING:** Selena says she has psychic powers.

**ANALYSIS:** The conclusion is about what happens if we find out whether Selena is correct. Selena’s claim is either true or not true: she has psychic powers, or she doesn’t.

Note that “find out whether Selena’s claim is true” covers both finding out the claim is true and finding out that it’s false. It’s best to think about what happens in *either *case:

- Claim true ➞ Selena psychic ➞ psychic possible
- Claim false ➞ Selena not psychic ➞ ?????

So we have an asymmetry. If we find out Selena’s claim is true, then we *do *know psychic powers are possible. But if the claim is false, we can’t make a general conclusion. Someone else could be psychic even if Selena isn’t. So to solve this question we have to somehow show that if Selena is not psychic then no one is psychic.

Note that I haven’t followed a traditional diagramming structure on this question. That’s because LSAC wrote this question in such a way that a traditional diagramming structure isn’t helpful. This question is more of a decision tree.

___________

- So? Selena still might or might not have powers. Or someone else could, even if Selena doesn’t.
**CORRECT.**This covers the gap from the analysis above. Now if Selena’s claim is false we will also know psychic powers are impossible.

This answer’s contrapositive is clearer:

~~Selena powers~~➞~~possible to have powers~~- This is a
*necessary*condition for the conclusion, but it doesn’t prove the conclusion correct. This is a sufficient assumption question. - This destroys the argument! We’re trying to prove the argument correct.
- This is just a mistaken reversal of the conclusion. It doesn’t help prove the conclusion.

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Martin Levy says

First, let me thank you on your explanations. I’ve found them to be one of the biggest blessings in my LSAT prep thus far and am incredibly grateful for the service you provide.

I was hoping you could elaborate on the asymmetry part of the analysis below:

“Note that “find out whether Selena’s claim is true” covers both finding out the claim is true and finding out that it’s false. It’s best to think about what happens in either case:

Claim true ➞ Selena psychic ➞ psychic possible

Claim false ➞ Selena not psychic ➞ ????? ”

I’m confused to how the wording of the stimulus sets up this asymmetry. What in the wording indicates the true or false. Is it the word “whether”? I feel that this question is a departure from the norms of most logical reasoning questions and am worried I won’t be able to identify a similar reasoning structure in another question.

FounderGraeme says

It’s the “if we find out whether Selena’s claim is true”. The whether means it might be true, and it might not be. And then the stimulus says “we will thereby determine whether it is possible”, which means that if the conclusion is true we will find out either way.

Sabrina says

Hi Graeme,

This was SUPER helpful!! I noticed you said this was “more of a decision tree” question rather than one that relies on traditional diagramming. Could you please elaborate a little on that?

TutorLucas (LSAT Hacks) says

The traditional method of finding the answer to a sufficient assumption question that uses conditional reasoning is to draw out each of the conditional statements in the stimulus, and come up with the missing conditional statement that will link the premises to the conclusion.

This question requires a bit more of a creative approach. In very basic terms, a decision tree is just a (tree-shaped) graph or model that is used to show all or some of the possible outcomes of a series of possible decisions. In the analysis for this question, Graeme used branches of a decision-tree to show the potential outcomes of investigating Selena’s claim to being a psychic. Her claim can only be true or false, so those are the two branches.

Branch 1: Her claim is true, she’s a psychic, and it’s possible to be a psychic.

Branch 2: Her claim is false, she’s not a psychic, and from there we have no idea what’s the case.

This decision-tree just provides a clear representation the gap in the argument, more so than just traditional conditional diagramming would. And determining the gap between the premises and conclusion is one of the most important factors in coming up with the correct answer to a sufficient assumption question.

Zach says

Thank you for this, very helpful! I agree the contrapositive makes the answer much clearer.

MemberHari says

your contrapositive in your explanation doesn’t appear to be correct

stimulus:

selena powers -> powers possible

contrapositive

powers not possible -> Selena no powers

your “

~~Selena powers~~➞~~possible to have powers~~” is a negation without reversalTutorLucas (LSAT Hacks) says

The analysis for (B) is showing the diagram of the contrapositive of the

answer choiceand not the stimulus.The answer choice says “If it is possible to have psychic powers, then Selena has them.”

The contrapositive of this answer choice (as the explanation notes) is: ~(Selena powers) –> ~(possible to have powers)