Sufficient Assumption - Page 91

[all_boost]

At the top of page 91, the book suggests that a correct sufficient assumption would be:

(If laws against gambling can't be enforced, they are ineffective)

I completely understand why this would be correct. My question is, under the pressure of time, why would it be wrong for me to rearrange the conditional and determine a sufficient assumption to be:

(If a law is ineffective, it is also unenforceable)?

This seems (and please correct me if I am wrong) to fill the arrow enough to justify the conclusion... In which case it would lead me to the incorrect answer choice B) rather than A).

Thank you in advance!

[all_boost]

Just figured it out!

The alternate assumption I suggested is flawed/would not be sufficient because we only know that the gambling law is unenforceable. The premise would have had to state that the gambling law is also ineffective for my alternate assumption to be sufficient.

[ManhattanPrepLSAT1]

Glad you were able to figure this one out. Your question is a classic case of what we call reversed logic. If I had $1 for every time a student committed a reversal on a conditional statement, I'd be retired. it's simply the most common reasoning error committed on the LSAT.

So a rule that says:

If something is a banana, then it must be a fruit

B ---> F

Does not mean that

F ---> B

If something is a fruit, then it must be a banana.

Obviously there are many other varieties of fruit besides bananas.

The test-writer knows that we can see that there must be a relationship between two things, but that's just the beginning of the battle. The question becomes, what does that relationship look like.

B ---> F (all bananas are fruit)
F ---> B (everything that is a fruit is a banana)
~B ---> F (anything that is not a banana is a fruit)
B ---> ~F (no bananas are fruit)

There are so many relationships that can exist between two different terms, that one must be very careful about which relationship represents the gap in the reasoning.

Nice work though all_boost!