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Necessary Assumption Help!!

mzthaidumplingmzthaidumpling Alum Member
edited April 2019 in Logical Reasoning 83 karma

Hello,

I have trouble seeing if something is actually required, even after applying the negation test and asking myself if the AC is giving more than is required, or fills the gap and is not actually required. If anything, I tend to see that the Negation Test wrecks the argument more often that I should, and wrongly choose that one thing that seems seemingly unrelated but I thought would wreck the argument.

Ex) Because we locked the door, no one can break into our house
A. Required: there are no other ways to break into the house
B. Required: one cannot break into the house going through the chimney
C. Not required: None of the windows can be opened
D. Not required: The door is the only way in and out of the house, and the lock is impenetrable.

I see why A and B is required. But I don't really see why C are D are not. I can see why D offers information that is extra, "and the lock is impenetrable", but why is C not required? Negation for C: Some of the windows can be opened. Doesn't that wreck the argument? Someone can break in now. What is the difference between C and B?

Another example:
When exercising the muscles in one's back, it is important to maintain a healthy back, to exercise the muscles on opposite sides of the spine equally. After all, balanced muscle development is needed to maintain a healthy back, since the muscles on opposite sides of the spine must pull equally in opposing directions to keep the back in proper alignment and protect the spine.

Which of the following is an assumption required by the argument?

A. Muscles on opposite sides of the spine that are equally well developed will be enough to keep the back in proper alignment.
B. Exercising the muscles on opposite sides of the spine unequally tends to lead to unbalanced muscle development.

Equally exercise muscles->pull in equal directions->healthy back.

I chose A. Negation: Muscles on opposite sides of the spine that are equally well developed WILL NOT be enough to keep the back in proper alignment. I know stating something is important doesn't mean that it alone will be sufficient to produce the outcome, but it seems to wreck the idea that this is important to do (conclusion). I know it's not 100%, but neither is B to me.

I eliminated B immediately glossing over it because we are talking about spines that are exercised equally, not unequally. Negation: Exercising the muscles on opposite sides of the spine unequally DOES NOT tend to lead to unbalanced muscle development. It wrecks the idea that exercising both sides equally is important. Why do I have to exercise both sides of my back equally if when I am exercising them unequally, it doesn't produce unbalanced muscle development anyway? But how is this a better answer that A? If anything I think it is more out of scope than A. We aren't specifically talking about spines that are not exercised unequally or unbalanced muscle development. Yeah, not exercising both sides equally may not produce the outcome of unbalanced muscle development, but I am not trying to avoid unbalanced muscle development, I am trying to fulfill balanced muscle development. What is not necessary to produce an outcome doesn't mean it should be neglected!

I hate "understanding" the questions only after the fact. I want to really understand how to tackle these types of questions.

Does anyone know any tips/tricks/insights that will help with other questions like these onward?

THANK YOU :)

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Comments

  • mzthaidumplingmzthaidumpling Alum Member
    83 karma

    Oh. Normally when we talk about something being "expensive" and then the AC talks about something being cheap, it's wrong because it is out of scope, and there are variations between (expensive, fair, cheap, very cheap). But in this instance, the opposite of unbalanced is balanced. There is nothing in between. Is that why it isn't out of scope? Same for equally/unequally.

  • BinghamtonDaveBinghamtonDave Alum Member ⭐ 🍌🍌
    8694 karma

    Simply "opening" the window does not wreck the argument. The window can open one inch and be impenetrable for a human to fit into to break into. The difference between B and C is that B actually actively disqualifies a potential route into the house.

  • GeeVee03GeeVee03 Member
    28 karma

    What really helps me is to think about the answer choice that absolutely must be true in order for the argument to hold. With C, for example, it could be true, but it doesn't HAVE to be. Not being able to open the windows doesn't absolutely mean that no one can break in. What if a thief breaks in by climbing through the chimney? The correct NA answer will always be one that not only CAN be true, but it MUST be.

    Hopefully this makes sense or gives some guidance :)

  • vitamincoverdosevitamincoverdose Member
    edited May 2019 615 karma

    I’m not 100% sure my approach is right, but here is how I do it... please let me know if there’s anything I’m missing.

    As for the first example, what I do is to come up with an example/a method that would make the negation irrelevant. I ask myself, “so what if some of the windows can be opened? How big are they?” I wouldn’t actually say that in my mind but rather have an image of a house with small windows where the windows open and intruders are stuck. It seems unnecessarily long when written down, but happens a lot faster in my mind…

    For the healthy back question,

    My task:
    The argument doesn’t stand without the correct answer. What’s the assumption you need to make for this argument to be absolutely true?(MBT) Find the P and C, have an idea of the assumption made, and move on to ACs.

    When exercising the muscles in one's back, it is important, to maintain a healthy back, to exercise the muscles on opposite sides of the spine equally. After all, (balanced muscle development) is needed to maintain a (healthy back), since the muscles on opposite sides of the spine must (pull equally) in opposing directions to keep the back in (proper alignment) and (protect the spine).

    -healthy back -> balanced muscle development
    -exercise equally -> proper alignment +protect the spine
    ————————————————————————
    -Healthy back -> exercise equally

    Argument is assuming there’s a relationship between balanced muscle development and exercise equally.

    AC could discuss about this. Not always true, and not always helpful for NA, but I personally found it helpful to have a concept of the big and clear assumption the author has made before going into ACs.
    But should be open to completely different looking assumptions as well.

    Which one of the following is an assumption required by the argument?

    A. Muscles on opposite sides of the spine that are equally well developed will be enough to keep the back in proper alignment.

    Enough to keep proper alignment? The stimulus doesn’t mention anything about anything being enough. It says balanced development is needed. NC =/= SC
    And is ‘well developed muscles’ same as ‘balanced developed muscles?’

    Negation: Muscles on opposite sides of the spine that are equally well developed will not be enough to keep the back in proper alignment.
    So what? It does nothing to the argument. All we know is that we need balanced developed muscles, but there can be other things also needed. Maybe we also need to have proper posture in addition to the well developed muscles. They could be both needed for healthy back.

    B. Exercising the muscles on opposite sides of the spine unequally tends to lead to unbalanced muscle development.

    Seems somewhat similar to the prediction: Balanced muscle development -> exercise equally

    Negation: Exercising the muscles on opposite sides of the spine unequally does not to lead to unbalanced muscle development.
    => Exercise unequally could lead to balanced muscle development => no need for exercise equally => argument destroyed

    As far as this the balance and equality goes, there’re only two options.
    It’s either balanced or unbalanced / equal or unequal.
    (Not exercise equally) and (exercise unequally) are the same.
    So are (unbalanced muscle development) and (NOT balanced muscle development.)

    If there’s no relationship between unbalanced muscle development and exercise unequally, there’s no relationship between the opposite as well.

    This means exercise equally and balanced muscle development have no relationship. If there’s no relationship between the two, why exercise equally for healthy back? => destroys the argument

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