Selena claims to have psychic powers. So if we find out whether Selena's claim is true, we will thereby determine whe...

Claire on May 27, 2019


Why is the answer B and not C? Thanks.

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Ravi on June 8, 2019


Happy to help. Let's take a look at (B) and (C).

This is a strengthen with a sufficient premise question, so we're
looking for the answer choice that, if true, makes the argument valid.

If we're able to find out that Selena does possess psychic powers,
then it makes sense to say that we've determined whether or not
psychic powers are possible. However, what if we find out that her
claim is false? Does her claim being false prove that it isn't
possible to have psychic powers? Not necessarily, as someone else
could have them.

Thus, we must make the assumption that Selena is the only individual
who could possess psychic powers. This way, if we figure out that she
has them or doesn't have them, we will definitely be able to know
whether or not it's possible for someone to have psychic powers.

(C) says, "It is possible to determine whether Selena has psychic powers."

The problem with (C) is that it does not help us to know what happens
if Selena does not possess psychic powers. It's still possible that
someone else has psychic powers. The conclusion of the stimulus, that
we would know whether or not psychic powers are possible even if we
discover that Selena doesn't have them, would not be justified with
(C), so it's out.

(B) says, "If it is possible to have psychic powers, then Selena has them."

(B) is great because it ensures the argument's conclusion. (B)'s
contrapositive is if Selena doesn't have psychic powers, then it's
impossible to have them. This tells us that whether we find that
Selena has psychic powers or not, we'll be able to know if it's
possible or not possible to have psychic powers. Thus, (B) is correct.

Does this make sense? Let us know if you have any more questions!

on September 10, 2019

@Ravi your explanations for B and C are great; can you explain why A is incorrect as well? Thanks!

Shunhe on December 22, 2019

Hi @Minerva,

The problem with A is that it doesn't ensure whether it is possible to have psychic powers or not. It also doesn't connect any general claims to Selena. Hope this helps.

fady on August 19, 2020


Not S ---> Not P

Selena having it a the necessary condition how is it that we conclude the sufficient backwards here?