December 1991 LSAT Section 4 Question 7

To become an expert on a musical instrument, a person must practice. If people practice a musical instrument for thre...

#JW on October 11, 2019

Could you please diagram this?

Please diagram this, it was a fallacy of reversal but I was able to deduce this not through diagramming but through reading the passage only. Thanks.

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Irina on October 11, 2019

@Jwebb,

If you can detect a flaw without diagramming, that's even better!
We would diagram these statements the following way:

To become an expert, a person must practice. In other words, if one is an expert, he must have practiced.

(1) E -> P

If people practice for 3 hours a day, they will usually become experts. In other words, it is sufficient to practice 3 hrs a day to become an expert.

(2) P3x -> E

Therefore, if a person is an expert, he must have practiced 3 hours a day.

(3) Therefore, E -> P3x.

This is an invalid inference as the proper transposition of premise (2) is:

~E -> ~P3x

IF one is not an expert, THEN it must be true that he/ she did not practice 3 hours a day.
This is a fallacy of mistaken reversal as you correctly pointed out.

#JW on October 12, 2019

Exactly, basic fallacy of reversal. The real thing with these are that the answer choice don't just say "fallacy of reversal" so how do you tackle that with respect to selecting the best answer choice when it is written in the form of the fallacy or what the fallacy fails to account for?

mkesh on May 12, 2020

i have this same question as well. thank you

Emil-Kunkin on August 21 at 12:54AM

The right answer describes what an illegal reversal will look like, it is an example of the sort of error that occurs when we commit an illegal reversal.