October 2010 LSAT Section 1 Question 17

Which one of the following assertions from passage A provides support for the view attributed to Maritain in passage ...

megmcdermott on August 20, 2019

Example 1 - Video Lesson

Question 1 presents the following condition: FKPW > HPM & LC Making the contrapositive: not LC or not HPM > FKPW When answering this question, I did pick the correct answer (D) but that is because I only realized that ONE of the sufficient conditions from the contrapositive was being invoked. However, Mehran points out that BOTH sufficient conditions are in fact being invoked in answer choice D. When he noted that I thought that I had picked the wrong answer because it was invoking both sufficient conditions instead of only one of them. Can someone provide some clarification on how D can be the correct answer even though both sufficient conditions are invoked? I thought that OR meant only one condition could be present in the correct answer...

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Bhavraj on September 2, 2019

When there is use of “or” as mentioned in the contrapositive argument of the principle in this case, In order to conclude the necessary condition (absence of the sufficient condition in the positive argument structure), you must invoke AT LEAST 1 of the sufficient conditions (absence of the necessary condition in the positive argument structure).

So “or” can be understand as AT LEAST 1, meaning invoking both is still a valid argument.

The PR in Q1 is as follows in S & N terminology:
FKPW —> HPM & LC
not HPM or not LC —> not FKPW

The PR in Q1 is as follows using words:
If the failure to keep a promise is considered to be wrong (FKPW), then the person to whom the promise was made must have been harmed (HPM) and discovery of the failure made everyone who discovered it lose confidence in that person’s ability to keep promises (LC). If the person to whom the promise was made to was not harmed (Not HPM), OR at least one person who discovered the failure did not lose confidence in the person’s ability to keep promises (Not LC), then we can conclude the failure to keep a promise was not wrong (Not FKPW).

D)
P: Not HPM (Miriam did not need the money)
P: Not LC (Miriam did not lose confidence in Carlo’s ability to keep secrets)
C: Not FKPW (Carlo’s failure to keep promise of Miriam was not wrong)

So for answer choice D, since the 2 premises tell us that Miriam did not need the money (Not HPM) and she did not lose confidence in his ability to keep promises (Not LC), we can accurately conclude that Carlo’s failure was not wrong (Not FKPW).

The key thing to understand here is that though we only needed one of the sufficient conditions in the contrapositive argument (as indicated by or), having both is also valid, although both are not required to conclude the necessary condition.

Hope this helps!