Q24 - A person's failure to keep

[LSAT-Chang]

I have one general question about this problem.
If (D) had met just ONE necessary condition and not BOTH, would it be wrong?
So basically, since the argument gives TWO necessary conditions (using the word AND) that needs to be met, we could split the thing into two (just like how the strategy guide shows us):

failure to keep promise is wrong -> harm
failure to keep promise is wrong -> lost confidence

Will there ever be an answer choice that meets only one of them and still be correct? Or does it HAVE to be the case that BOTH are met? I think the split just confuses me a little bit -- since I sometimes "overlook" one or the other and think that one would suffice, when in fact, the conditionals above clearly tell us that both "harm" and "lost confidence" happen if "failure to keep promise is worng" happens. I mean, the rest of the answers (A), (B), (C), and (E) clearly are reversed or don't have any of the necessary conditions met, but I was curious to know if (D) and possibly other answer choices would have been correct if it had met just ONE and not BOTH -- and if there is any problem in the past that does that.

[timmydoeslsat]

Love the avatar and good question.

The stimulus says:

Failure to keep promise is wrong ---> Harms person you made it to AND all who discover the failure of keeping a promise lose confidence in person.

Look at it like this:

If A ---> B & C

What happens if we do not have C?

You do not have A.

At this point we could not care less about B and whether or not this variable is present. We know that since C is not there, A will not be there.

You can have an answer choice that address only one part of that necessary assumption to show that the sufficient condition could not possibly exist.

Also notice in this problem that we can only conclude what is not wrong!

We can never conclude what is wrong!!!

This is because wrong is the sufficient condition and we do not know if we have that case or not.

So this quickly eliminates B, C, and E.

It is down to A and D.

A's conclusion is about Ann KEEPING her promise not being wrong. This is twisting the stimulus. Our condition about what is not wrong is failure to keep a promise not being wrong.

Thus only left with D.

D says that Miriam did not lose confidence in Carlo's ability to keep promises. This means that one of the necessary conditions in the stimulus will not be met, thus we know that the failure to keep the promise was not wrong.

As for the other necessary condition of harming the person the promise was made to...we do not need to know this since it was so clear that the other necessary condition was clearly violated.

However, for the sake of clarity, I would argue that we are not sure if Miriam was harmed. We know that she did not need the money, but perhaps there was some type of harm done that we do not know about. I think that necessary condition is a little dicey.

[LSAT-Chang]

Love the avatar and good question.

I love my avatar too! Hopefully I do destroy it lol anyways, so are you saying that if we have in the argument A -> B + C, and let's say for example an answer choice has ~C -> ~A, it would be correct? But what about B? Are you saying that that doesn't matter? I would think that it is an incomplete answer if it just had ~C -> ~A since it should be ~C or ~B -> ~A.. right? I made another post yesterday night about a problem which exactly expresses this and which I do not understand how the answer choice, even if incomplete, is in fact, the correct answer. Here is the post that I made: q11-a-gift-is-not-generous-unless-t335.html

[timmydoeslsat]

so are you saying that if we have in the argument A -> B + C, and let's say for example an answer choice has ~C -> ~A, it would be correct? But what about B? Are you saying that that doesn't matter? I would think that it is an incomplete answer if it just had ~C -> ~A since it should be ~C or ~B -> ~A.. right?

I will address the other post in its respective topic. Thanks for that.

As for the quoted part above. It is not typical for the LSAT to have a situation of going from:

Stimulus: A ---> B & C

To just " ~C --->~A " in an answer choice.

However, it would still be a correct answer choice.

Think of it abstractly. To have A, you must have two necessary variables, B and C.

If you lack C, then you will not have A. When you know for a fact that you do not have C, the situation of B is irrelevant in the scheme of a "A ---> B & C" stimulus.

There is no incomplete aspect of going from ~C ---> ~A

Also, notice that if you have a stimulus of "A ---> B & C".......

What happens if you have B & C present?

Nothing! We know nothing when B and C happen! Do we know what happens when B and/or C is out? Yes!

[giladedelman]

Timmydoeslsat, I freaking LOVE your explanation of this problem, especially your point about how the given conditional statement only allows us to conclude that something is not wrong, not that something is wrong. That understanding is a really powerful tool on these Principle Example questions.

To add on to your explanation about necessary/sufficient:

A --> B and C means that if you have A, you have to have both B and C. But what it does not mean is that B and C have to do everything together.

Take a real-world example. If you are a human who is alive, you must have oxygen and water.

Alive --> O and W

Now, if I take away all your water, and I'm really sorry about this, you will die. You could be surrounded by all the oxygen in the universe, but if you have no water, it doesn't matter. And the same thing is true if I deliver fifty tubs of Poland Spring drinking water to your house, but suck all the oxygen out. Taking away either necessary condition is enough to ensure that we can't have our sufficient condition. So these statements are both accurate on their own:

-O --> -Alive

-W --> -Alive

This would also be accurate:

-O and -W --> -Alive

But you don't need to negate them both. That's the whole point of being necessary: if you take any one necessary condition away, the thing falls apart.

Remember, our job is to pick an answer choice that obeys the principle, not one that necessarily talks about every single element in it. Our question is, is this accurate according to the conditional statement given?

Hope that helps!

[LSAT-Chang]

Take a real-world example. If you are a human who is alive, you must have oxygen and water.

Alive --> O and W

Now, if I take away all your water, and I'm really sorry about this, you will die. You could be surrounded by all the oxygen in the universe, but if you have no water, it doesn't matter. And the same thing is true if I deliver fifty tubs of Poland Spring drinking water to your house, but suck all the oxygen out. Taking away either necessary condition is enough to ensure that we can't have our sufficient condition. So these statements are both accurate on their own:

-O --> -Alive

-W --> -Alive

This would also be accurate:

-O and -W --> -Alive

But you don't need to negate them both. That's the whole point of being necessary: if you take any one necessary condition away, the thing falls apart.

Remember, our job is to pick an answer choice that obeys the principle, not one that necessarily talks about every single element in it. Our question is, is this accurate according to the conditional statement given?

Hope that helps!

I totally get it now. That example greatly helped! The other post that I made is what I was referring to, since the correct answer choice does have only "~C -> ~A" and so I thought it was incomplete since it misses B, but you are right -- not having C is sufficient to prove no A, since A needs BOTH! So if you don't have one or the other, the argument can't hold! Thanks for the great explanation both of you guys! =)