PT9 S4 Q04

Natalie.endenburg

Lately I have been having a lot of trouble with "must be true" questions. Can anyone explain why C was the correct answer choice for this question, and not D?

Thank you!

Law and Yoda

This looks like valid argument 1

If A then B
so
If not B then not A

The passage is saying this essentially:

DF (Democracy functions well) -> Moral + Intelligent

Moral or Intelligent -> DF (this is the contrapositive)

C is the Contrapositive of the original statement and is thus the correct answer.
D is is a Mistaken Negation of the original statement because it negates the sufficient and necessary conditions without reversing them.

dazedandconfused-1

If we translate the question stem to a set of conditionals, it will look like:
"if a democracy functions well, then the electorate is moral and intelligent." or
DFW --> M and I.

The contrapositive of this is (using DeMorgan's Law) : not M or not I --> not DFW.

C states the contrapositive: "If the electorate is not moral or not intelligent, then a democracy will not function well. D says not DFW --> not M or not I, which is a mistaken reversal.

Hope this helps!

Natalie.endenburg

Thank you very much to both of you for your help!