Q21 - Most people who become

[ManhattanPrepLSAT1]

Question Type
Match the Flaw

Stimulus
This argument mixes up the direction of the comparative quantifier. Here's a simpler analogy. Does it follow that most company employees are on the board of directors at company XYZ, from the claim that most members of the board of directors at company XYZ are employees of the company? No. And same with this argument. It could be that a majority of migraine sufferers were never prone to bouts of depression as children.

Anticipate
That most A's are B's, does not prove that most B's are A's.

Correct Answer
(A) mixes up the comparative quantifier in the same way as the argument above. That most good-tempered dogs received a vaccine for rabies does not prove that most dogs that receive a vaccine for rabies become good-tempered dogs.

Incorrect Answers
(B) relies on a comparative quantifier that moves in a logical direction and so doesn't contain the same flawed method of reasoning. That said, the argument doesn't account for the possibility that a dog may have been mistreated by a previous owner rather than the current owner.

(C) contains flawed reasoning, but a different flawed method of reasoning than that in the stimulus. This argument tries to contrapose a "most" statement.

(D) is like (C) and contains a different flaw. This argument fails to consider the relative frequency of which pets are dogs. Only if dogs were neither more nor less common than other pets would this reasoning stand.

(E) relies on a comparative quantifier that moves in a logical direction and so doesn't contain flawed reasoning.

#officialexplanation

[seychelles1718]

can this be also classified as a reverse logic flaw?

[ohthatpatrick]

In a fuzzy sense, sure. It's definitely a reversal.

Normally, when we use the term reversed logic or "illegal reversal", we're referring to conditional logic.

This is NOT that, since "most" statements are not certain; they leave room for exceptions.

But -- it's still true that "most" statements have a picky left to right order and you cannot interpret them backwards.

Otherwise, I could make this terrible argument:
Most Senators are male.
Kanye West is male.
Thus, Kanye West is probably a senator.

So I would have been thinking to myself on this question, "The flaw is that he tries to reverse the logic of a Most statement".

[creek1262]

Hi, I still don't understand why B is wrong.
I kept both A and B as contenders and chose B in the end.

Could you please further explain this?
Thank you!

[ohthatpatrick]

The structure of the original argument is this:

Most things that are X were Y.
Thus, something that is Y is likely to be X.

X = migraine sufferer as adult
Y = prone to depression as a child


(A)'s structure
Most things that are X were Y.
Thus, something that is Y is likely to be X.

X = good-tempered dog
Y = vaccinated as a puppy


(B)'s structure
Most things that are X were Y.
Thus, something that is X is likely to have been Y.

X = vicious dog
Y = ill-treated when young


(B) is wrong because it's conclusion is still X to Y.
The original and the correct answer (A) go from Y to X.

Let me know if that doesn't make sense.