Hi Jocelyn,
Your diagramming is great, and your reasoning is sound when it comes to looking for the concepts that need to be connected. Here's how to take that last step so that you can be certain about what you're looking for in the answer choice.
First, think about what you're given (in the premises). In this case, you correctly identified the relevant conditional that you were given in the premises as: NOT honest out of respect for morality
NOT praiseworthy.
Second, think about what you're trying to prove (in the conclusion). You also correctly identified what you're trying to prove: concerned for own well being
NOT praiseworthy.
What you need to find is an answer choice that you can "hook" to the premise you're given that, when hooked to the premise, will produce the conclusion you're trying to prove.
So let's look at answer choice C in that light. It diagrams as: performed out of respect for morality
NOT concerned for own well being.
That can't be hooked up to the premise
as it stands because the shared term (performed/honest out of respect for morality) is stated in the negative in the premise, and in the positive in the answer choice.
So check the contrapositive of answer choice C, which diagrams as: concerned for own well-being
NOT performed out of respect for morality.
This CAN be hooked up to the premise, like so: concerned for own well-being
NOT performed out of respect for morality
NOT praiseworthy. Does that give us the pieces we need in the conclusion? Yes, because going from the first link to the third link of that chain is the proof of the conclusion.
How would we know that another answer (say, the Mistaken Reversal of answer choice C) would not work to prove the conclusion? We would diagram it (and its contrapositive) and we would see that there would be no way to hook it to the
premise, either way we diagram it.
You can tell from this discussion that diagramming really is a savior when it comes to being certain on such questions. The better and more confident you continue to get with diagramming, the easier these questions become.
On your second question, answer choice E is a bit broad to be a necessary assumption here. The argument only concerns the narrow issue of what is
morally praiseworthy for someone (in this case, Downing), so it doesn't need to make any sweeping assumptions about
morality in general. If the answer were watered down a bit to say "Morality demands that one be honest
in at least some cases where this could be detrimental to one’s own well-being," then I might consider that closer to a necessary assumption.
I hope this helps!
Jeremy Press
LSAT Instructor and law school admissions consultant
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https://twitter.com/JeremyLSAT