#14 - Some of the world's most beautiful cats are Persian

[Administrator]

Complete Question Explanation


Must Be True—Formal Logic. The correct answer choice is (E)

The stimulus does not contain a conclusion and can be diagramed as follows:

          BC = world’s most beautiful cats
          P = Persian cats
          Po = pompous
          I = irritating

LR1.PNG

Because the question stem is a MustX, you should expect to see all of the above inferences as wrong
answer choices.

Answer choice (A): This is the second inference, and therefore the answer is incorrect.

Answer choice (B): This answer choice is identical to answer choice (A)—remember to expect the
reversibility of statements to be used by the test makers.

Answer choice (C): This is the contrapositive of the third inference.

Answer choice (D): This is the first inference, reworded to reflect the reversibility of the statement.

Answer choice (E): This is the correct answer. Notice that the presence of some are not should
have been a tip off that this answer was problematic because the only possible negative in a valid
inference would be via the contrapositive of the third inference.

[LSAT2020]

I was stuck between C and E. Would really appreciate seeing the stimulus diagrammed. To me it seemed like it was very conditional heavy. Thanks in advance!

[Jeremy Press]

Hi LSAT2020,

Sure, happy to help with a diagram!

First, an abbreviation key:
World's most beautiful cats = WMB
Persian cats = Persian
Pompous cats = Pompous
Irritating cats = Irritating

The first claim should be diagrammed as: WMB Persian
The second claim should be diagrammed as: Persian Pompous
The third claim should be diagrammed as: Pompous Irritating

All these claims can be chained together: WMB Persian Pompous Irritating.
The contrapositive of the arrow chain from Persian to Pompous to Irritating is: Irritating Pompous Persian.
Just a reminder that "some" arrows don't get contrapositives.

A few inferences can be drawn from these chains:
1. Some of the world's most beautiful cats are pompous. (Answer choice D!)
2. Some of the world's most beautiful cats are irritating. (Answer choices A and B!)
3. All Persian cats are irritating.
4. If a cat is not irritating, then it is not Persian (this comes from the contrapositive chain) (Answer choice C!)

You're right that this stimulus is heavy on the conditionals, and you should use the diagram and the connections it validates to eliminate all solid inferences, leaving you with answer choice E.

I hope this helps!