December 2017 LSAT Section 1 Question 25
Any popular television series that is groundbreaking is critically acclaimed. But not all popular television series a...
2 Replies

Irina on October 7, 2019
Let's look at the structure of the argument.Any popular television series (P) that is groundbreaking (Q) is critically acclaimed (R)
P ^ Q -> R
Contrapositive of this statement is :
~R -> ~P v ~ Q
If a show is not critically acclaimed, it is either not popular or not groundbreaking.
But not all popular television series are critically acclaimed.
This statement tells us that P is true but R is false - popular but not acclaimed. We can see from the first premise, that if R is false, then either P or Q must be false:
~ R -> ~P v ~ Q
Since we know that P is true, we can conclude that Q is false (not all shows are groundbreaking)
Therefore, ~Q.
Let's look at the pattern of reasoning in (C) & (E):
(C) If biography is unbiased (P), it contains embarrassing facts (Q) about the subject.
P -> Q
The contrapositive of this premise is:
~Q -> ~P
Since not all biographies contain embarrassing facts (~Q), then not all biographies are unbiased.
~Q
Therefore, ~ P
This is a valid argument, per premise (1), we can conclude that if ~Q is true, then ~P is true.
Let's compare it to (E):
If a book is worth reading (P), it is worth buying (Q)
P -> Q
Since not all books are worth reading, not all books are worth buying
~P
Therefore, ~Q
This is in an invalid argument as it commits a logical fallacy of mistaken reversal. We can only conclude that ~Q -> ~P (a proper contrapositive of the first premise), we cannot conclude ~Q when ~P is true.
Let me know if this makes sense and if you have any further questions.
~
on January 21, 2021
I am still not understanding why is E is incorrect?