People who have never been asked to do more than they can easily do are people who never do all they can. Alex is som...
LadyMaeJanuary 26, 2019
Difference Between A and B
I can't see the logical difference between A and B other than that B just reversed the contrapositive whereas A reversed the initial statement... is that why A is right and B isn't, because A reversed the original statement like the question stem did?
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Happy to help. The difference between (A) and (B) is huge—A is invoking the necessary condition to conclude the sufficient condition, whereas (B) is negating sufficient condition in order to conclude the negation of the necessary condition. Let's take a look.
The stimulus says people who have never been asked to do more than they can easily do are people who never do all they can.
Never been asked to do more than they can easily do - ->people who never do all they can
This is an A - ->B statement
Then, we're told that Alex is someone who has clearly not done all that he is capable of doing. In other words, Alex is a member of the B group.
The argument then concludes that Alex has never been pushed by anyone to do more than what comes to him easily. The argument's conclusion is A
The full structure of this argument is
A - ->B
B
Therefore, A
This is incorrect conditional logic, and this is the flaw. it's invoking the necessary condition and saying that the sufficient condition comes from invoking the necessary condition.
Answer A says that anybody who has a dog knows the true value of companionship.
has a dog - ->knows value of companionship
A - ->B
We're then told that Alicia has demonstrated that she knows the true value of companionship. In other words, Alicia is a subset of group B.
The argument then concludes that Alicia has a dog. In other words, the argument concludes A
A - ->B
B
Therefore, A
This flawed argumentation structure replicates what we see in the stimulus, so this is the correct answer.
Answer B is incorrect because although ti's flawed reasoning, the flaw is not identical to the flaw found in the stimulus.
(B) says that anyone who discovers something new is someone who has examined all the possible solutions to a problem.
Discovered something new - >has examined all possible solutions
This structure is A - >B. So far, so good.
(B) then says that Fran hasn't discovered something new and concludes that Fran has never explored all the possible solutions to a problem
/Discovered something new - >/Has examined all possible solutions
In other words, /A - >/B
See the problem here? (B) is failing the sufficient condition, and as a result, it's saying that the necessary condition is failed. This is incorrect logic, but it's also not the flaw exhibited in the stimulus.
The full structure of (B) is
A - >B
/A
Therefore, /B
If in order for (B) to have been correct, we would need it to say
A - ->B
B
Therefore, A
Does this make sense? Let us know if you have any more questions—we're here to help!
Motunrayo-Bamgbose-MartinsJune 11, 2020
But when you look at the contrapositive of B, wont that just be a reversal and not negation?
April 17, 2024
I too struggled to see the difference between A and B even after Ravi's explanation, but I think I figured it out. We get so focused on trying to learn to apply the formulas for diagramming that we fail to focus on the entire sentence. "Fran has never explored all the possible solutions..." -That is a negation. So even if it looks like B too is a reversal, the negation is obvious in the text. I hope I am on to something. I encountered this challenge in other questions as well.
April 17, 2024
Sorry, I meant to say "Fran has never discovered something new..." it is the same thing though. It appears as a negation.
