Q20 - Ethicist: Every moral action is the keeping of

[giladedelman]

20. (E)
Question Type: Matching
This is a tough one because of the quantifier overlap! We can diagram the pattern of reasoning like this:
All M are K
All K are S
Some K are not M
Therefore, some S are not M

Answer (E) matches this pattern:
All B are T
All T are D
Some T are not B
Therefore, some D are not B

By the way, is this logic valid? Let’s try an analogy: If all pants are clothing, and some pants are not denim, then we can certainly conclude that some clothing is not denim.

Notice also that the first part of the argument, that all M are K, doesn’t actually affect the core.

(A) doesn’t match up, and it’s redundant: some D are not C, therefore some D are not C.
(B) is logically flawed: all E is B, and all B are P. Some B are not E, therefore some E is not P. It would be correct if it concluded instead that some P is not E.
(C) is valid, but has slightly different logic. Instead of "all A are B, all B are C," it gives us "all A are B, and all A are C." Tricky!
(D) is logically flawed: All Arc is D, and all D is Art. Some D is not Arc, therefore some Art is not D. It would be correct if it concluded instead that some Art is not Arc.

#officialexplanation

[mrudula_2005]

question: the second clause of the first statement says "...and keeping an agreement is nothing more than an act of securing mutual benefit." does that mean the arrow goes both ways? that an act of securing mutual benefit is both necessary AND sufficient since there is nothing more to keeping an agreement than that?

so would it be: K <--> S ?

because in that case, E would not be exactly parallel...

If this is not an "if an only if" clause, what would make it one?

thanks!

[goriano]

question: the second clause of the first statement says "...and keeping an agreement is nothing more than an act of securing mutual benefit." does that mean the arrow goes both ways? that an act of securing mutual benefit is both necessary AND sufficient since there is nothing more to keeping an agreement than that?

so would it be: K <--> S ?

because in that case, E would not be exactly parallel...

If this is not an "if an only if" clause, what would make it one?

thanks!

I paraphrased the clause as "Keeping an agreement is SIMPLY/ONLY/JUST an act of securing mutual benefit."

Although I can see how you might see it as a "double arrow" statement, I didn't interpret it as such based on my paraphrase.

But I would also love to hear from the LSAT geeks what would make this clause an "if and only if"!

[giladedelman]

As worded, I don't think it's "if and only if" because while keeping an agreement is "nothing more than an act of securing mutual benefit," that doesn't mean that every act of securing mutual benefit is the keeping of an agreement.

For example, I could say, "Celery is nothing more than a vegetable." That's true. So if we know it's celery, we know it's a vegetable. But that doesn't mean every vegetable is celery.

Dig?

[badalov90]

"(B) is logically flawed: all E is B, and all B are P. Some B are not E, therefore some E is not P. It would be correct if it concluded instead that some P is not E."

Just wanted to point out that the conclusion of answer choice (B) may still work given the fact that it is the contrapositive of the statement we need.

"Some E is not P" this is equivalent to "Some P is not E"... So, while answer choice (E) does match up perfectly, I do not understand why (B) would be wrong in light of my reasoning.

[giladedelman]

Thanks for the question!

In fact, "Some E is not P" is NOT equivalent to "Some P is not E." Let's use a more tangible example.

Some humans are not women. Can we flip that around and say, some women are not human? No, of course not. In fact, all women are human.

So saying "some X is not Y" is not a statement we can reverse. That's why it's not true that (B) gives us equivalent structure to (E).

Does that answer your question? All these letters are getting confusing ...

[NatalieC941]

I understand how E works, but not how I would chain the inferences if I was trying to make sense of it all.

I understand giladedelman's logic below,...

"In fact, "Some E is not P" is NOT equivalent to "Some P is not E." Let's use a more tangible example.

Some humans are not women. Can we flip that around and say, some women are not human? No, of course not. In fact, all women are human.

However, how do you actually chain the statements to sensibly know how to infer this?

All M are K
All K are S
Some K are not M
------------------------
Therefore, some S are not M


How would you reverse "Some K are not M" and how does this chain?

Thank you in advance!

[CourtneyH949]

How can you speed up on matching questions like this?
I currently have to diagram the conditional logic in the stimulus and all of the questions to find which answers match. Are there any faster ways to solve these problems?

[Laura Damone]

Hi! Forgive the delay here - technical difficulties!

These questions do take time, and frequently a bit more than other, shorter questions. That said, there are lots of ways to get through them efficiently!

If you have a conditional stimulus, definitely diagram it. Then, pause for a moment and look at your diagram. What features does it have that you'll need to match in the correct answer?

Now, time to evaluate A. Read it and assess whether it has the features you just identified. If it does, diagram to confirm. If it doesn't, eliminate without diagramming.

Also consider whether the answer has anything "extra" that doesn't match your original argument. So, for example, if the argument in the stimulus has 2 conditional premises and answer A only has 1, eliminate A without diagramming. If B has the 2 conditional premises but has an "extra" premise with an "either/or" structure, eliminate B without diagramming. If C has the 2 conditional premises and nothing extra, diagram to see if the premises reach the conclusion in the same way as they do in the stimulus. If they don't, eliminate. If they do, select the answer.

Matching questions are a lot like Logic Games questions. If you can prove an answer correct with your diagrams, go ahead and select it. Don't feel like you need to eliminate the other answers or even read them if you're confident in your diagramming!

One other strategy that you might try: ID the conclusion of each answer and eliminate any with a conclusion mismatch before considering any other piece of the argument. This is a great approach to non-diagramming Match questions!

Check out Drill 106, Know When to Fold 'Em, on page 610 of your 5lb book for some great practice!

Hope this helps!