PT 58 Sept 09 Section 4 Parallel Flaw Q22 Forum

[msuz]

I dont see why the flaw in Answer A and C arent both the same exact thing.

A) "Recipe follow exactly" + "HQ ingredients" then "Recipe turns out." Flaw- Arthur followed recipe exactly and it turned out, so Arthur used HQ ingredients.

C) "Cacti in Shade" + "Watered 2x Weekly," then "it will Die." Flaw- Cactus kept in the shade and it is dead, so It must have been watered 2x weekly.

They both seem to follow "If A+B then C," with a flaw of "Since A+C happened, B happened."

Someone please explain why this isnt so?

[lothsome]

I guess this one is pretty subtle, relatively speaking.

A says "only if:" "recipe will turn out only if..."

C does not.

The argument lacks the "only if" clause, therefore A, though the flaw is similar, is too strong, and C is the correct response.

[msuz]

hmm... so "only if" actually changes the argument to "if the recipe turns out," then Arthur "Followed the recipe exactly" + "used HQ ingredients?"

Whereas if it were to say "This recipe will turn out IF..." instead of "This recipe will turn out ONLY IF..." it would diagram as "Recipe follow exactly" + "HQ ingredients" then "Recipe turns out."

Just making sure, bc to solve these problems I usually use diagrams when Im stuck.

[lothsome]

Yes, your evaluation is correct. This is a necessary vs sufficient question, so the way you have illustrated the relation captures everything crucial.

You might also think about it like this: in the argument, we are told that two things will cause the end result (successful book tour) to occur, but we cannot infer that such conditions are the only conditions that will lead to a successful tour. It could also be a successful author and good weather will suffice for a successful tour.

On the other hand, A tells us that the recipe turns out only in the circumstances that the recipe is followed and HQ ingredients are used. There are no other possibilities that would suffice, therefore it is necessary that if the recipe turns out, the recipe was followed and HQ ingredients were used.

[msuz]

Thanks a lot.

You dont run into this type of logic as much on the LR section as much as LG, so I guess it caught me off guard.

[Obelisk18]

A isn't wrong "because it's too strong". It's wrong because it reverses the relationship. "Only if" always indicates that what follows is a necessary condition. So the first sentence of A turns out to be C => A+B. In the original, the first sentence is A+B=> C. Choice A isn't flawed.

[msuz]

A isn't wrong "because it's too strong". It's wrong because it reverses the relationship. "Only if" always indicates that what follows is a necessary condition. So the first sentence of A turns out to be C => A+B. In the original, the first sentence is A+B=> C. Choice A isn't flawed.

Thats clear now. Thanks!