All Labrador retrievers bark a great deal. All Saint Bernards bark infrequently. Each of Rosa's dogs is a cross betwe...

Angela on July 25, 2014

Help Plz

Why can't A work? Thank you!

1 Reply

Melody on July 30, 2014

You can click the "play button" image on the top right corner of the screen to access the video explanation.

Here we have an argument. Our conclusion is: "Rosa's dogs are moderate barkers." Why? We know that all Labrador retrievers bark a great deal, and that all Saint Bernards bark infrequently. We are then told that each of Rosa's dogs is a cross between the two.

Let's diagram.

"All Labrador retrievers bark a great deal."

PR1: LR ==> BGD
Not BGD ==> not LR

"All Saint Bernards bark infrequently."

PR2: SB ==> BI
Not BI ==> not SB

This is clearly a flawed argument. Just because Labrador retrievers bark a lot and Saint Bernards bark infrequently, we have no information on dogs that are a cross between them.

We are looking for the answer choice that uses the same flawed reasoning.

So to have the same flawed reasoning we need two Sufficient & Necessary sentences and then a combination of these two to conclude that we are somewhere in the middle of the necessary conditions.

Answer choice (A) states: "All students who study diligently make good grades. But some students who do not study diligently also make good grades. Jane studies somewhat diligently. Therefore, Jane makes somewhat good grades."

(A), while flawed, does not have the same flaw.

Let's diagram.

"All students who study diligently make good grades."

PR1: SD ==> MGG
Not MGG ==> not SD

"some students who do not study diligently also make good grades."

QS1: not SD-some-MGG
MGG-some-not SD

"Jane studies somewhat diligently"

P: SSD

"Therefore, Jane makes somewhat good grades."

C: SGG

Just because we have "somewhat" of the sufficient condition, does not mean that we have "somewhat" of the necessary condition. This, however, is not the same flaw as our passage. Thus, answer choice (A) is not our correct answer.

Hope that clears things up! Please let us know if you have any other questions.