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#17 - When exercising the muscles in one’s back, it is

jmaclan01
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I'm not sure if I broke this argument down correctly.

MHB :arrow: EMOE
MHB = Maintain healthy back
EMOE = Exercise muscles on opposite sides equally

I believe this is the conclusion while the second sentence is a premise. Does the second sentence contain a conditional statement as well? Also, is there a gap in assuming "exercising the muscles on opposite sides of the spine equally" is equivalent to "balanced muscle development"? I thought the assumption question might attack that gap.
Robert Carroll
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j,

This is an excellent start. The first sentence is the conclusion and you've identified the conditional form of it. You're also right that the second sentence is a conditional, with "balanced muscle development" being the necessary condition (because it says this is "needed") and "maintain a healthy back" the sufficient condition. Let "BMD" be an abbreviation for that necessary condition, and keeping the other abbreviations that you used in your post:

MHB :arrow: BMD

Because the conditional in the premise connects MHB and BMD, but the conclusion connects MHB and EMOE, it's natural to look for an assumption that connects EMOE to BMD. For instance, if the following were assumed:

BMD :arrow: EMOE

then, because there is a chain of conditionals, we could combine this with the second sentence to get what the conclusion says.

Look for the answer choice that connects those!

I think this discussion answers your question about the gap - "balanced muscle development" and "exercising muscles on opposite sides equally" have not yet been connected, and the correct answer choice in this question will connect them. That's because the assumption in this question is a Supporter Assumption - it closes the gap by linking elements together.

You were definitely on the right track with this one, and I hope this discussion allows you to understand what the right answer choice is.

Robert
jmaclan01
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I see the correct answer is linking the two but as a contrapositive. I appreciate your help!
moalkhaf
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Good morning. I was wondering if someone could look at this practice question from the 2007 LSAT and tell me if I used the assumption negation technique correctly. Not that the capitalized word is the negation.

When exercising the muscles in one’s back, it is
important, in order 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 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 NOT be enough to keep
the back in proper alignment.

(B) Exercising the muscles on opposite sides of the
spine unequally DOES NOT tend to lead to unbalanced
muscle development.

(C) Provided that one exercises the muscles on
opposite sides of the spine equally, one will NOT
have a generally healthy back.

(D) If the muscles on opposite sides of the spine are NOT
exercised unequally, one’s back will be
irreparably damaged.

(E) One should NOT exercise daily to ensure that the
muscles on opposite sides of the spine keep
the back in proper alignment

Why is C wrong. It directly contradicts what the author is arguing by claiming that excersizing the muscles on opposite sides of the spine equally will not lead to a healthy back
Francis O'Rourke
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Hi Moalkhaf,

The speaker's conclusion was that if you want to maintain a healthy back, you must equally exercise the muscles on either side of the spine.

The evidence given for this argument was that balanced muscle development is needed to maintain a healthy back.

Conclusion: MHB :arrow: EMOE
Premise: ... MHB :arrow: BMD

As Robert Carroll wrote above
Because the conditional in the premise connects MHB and BMD, but the conclusion connects MHB and EMOE, it's natural to look for an assumption that connects EMOE to BMD. For instance, if the following were assumed:

BMD :arrow: EMOE

then, because there is a chain of conditionals, we could combine this with the second sentence to get what the conclusion says.

Look for the answer choice that connects those!


Answer choice (B) connects the information perfectly! it states that NOT exercising muscles on either side equally usually leads to not balanced muscle development. Since the author is apparently assuming that balanced muscle development requires exercising muscles on either side equally, the argument must assume that not exercising muscles equally can lead to unbalanced muscles. If the author did not believe this, then there would be no reason to conclude that we need to exercise both sides equally.


Answer choice (C) tells us that a guaranteed way to maintain a healthy back is to exercise muscles on either side of the spine equally. If you want to diagram this statement, you can do so this way:

..... Exercise muscles on opposite sides equally :arrow: generally healthy back

The author did not attempt to make an argument about guaranteeing a healthy back, but what is necessary for a healthy back, so this statement is no necessary for the argument.

It is possible for the speaker to believe the logical negation of this answer choice and still make the argument. The logical negation of this answer choice is that "exercising muscles on either side does not necessarily guarantee a generally healthy back". Since the argument concerns what is required for a healthy back, it is okay if exercising muscles on either side does not always guarantee a healthy back.

It looks like the logical negation that you provided was too extreme. Make sure to remember that when you negate a conditional statement, you only negating the necessity of the relationship. So, the logical negation of ..... if A, then B ..... is ..... If A, then not necessarily B.