LR MLSAT LR Book p.105

[ivank]

Hello,

First of all, was wondering if this is the right place to post a question relating to the Manhattan LR Guide. Please let me know to avoid incorrect posting down the road.

On p. 105 of the book, the argument: "An automatic bell above the front door rings whenever a customer enters the front door of the Town Convenience Store. Therefore, one can accurately determine the number of customers who enter Town Convenience on any given day simply by counting the number of rings from the front door bell"

Assumption option 3: The bell never fails to ring whenever a customer enters the front door of the store.

Book's explanation: Premise booster! We already know this to be true...

Yes I agree it is a premise booster, but at the same time (this is where I am confused) does not "The bell sometimes fails to ring when a customer enters the front door of the store" destroy the argument? I mean if this is true, one cannot [always] accurately determine the number of customers who enter Town Convenience on any given day. This is confusion #1.

The other is, while negating is supposed to be true all of the time, this is an instance when doing so led me to the wrong place. Did I not negate properly? I think I did it ok. And while I was tempted to put "X" across this option, I thought of negating and got my thinking set up as above...and picked the wrong option (thinking "The bell never fails to ring" is required for this argument to be true)
I kind of thought..."the whole argument assumes that the ring never breaks down or the bell always functions properly" Can fail to ring = break, ever? Or the issue is that once it is said that "bell above the front door rings whenever" I have to assume it never fails to do so (seems to me that this is what the book assumes, and this where I need a confirmation or refutation) Hopefully you see what I am getting at...Please let me know where my thinking is not straight on the issues above and perhaps a better way to think about this particular example.

Regards,
Ivan

[ManhattanPrepLSAT1]

Hey Ivan,

Lets take your questions one at a time. First, I moved your post to the Curriculum forum as your questions are about MLSAT curriculum. Future questions of this sort can go here!

Confusion #1: The exercise on p105 is about finding the assumption of the argument. It's useful to think of the assumption as the space between the evidence and the conclusion. I think you may have the difference between the "conclusion" and the "argument" mixed up. We don't want to negate an answer to see if it destroys the conclusion, but rather negate an answer to see if it destroys the reasoning. So if you negate option 3, you may do serious damage to the conclusion, but you're not challenging whether the evidence leads to the conclusion. Mainly, because it directly challenges a premise.

Confusion #2: The negation test always works. The problem here is that it wasn't being applied properly. Sure, you were negating the statement perfectly, but you weren't asking the right question. You were asking whether the conclusion is undermined. But what you need to ask yourself is whether the reasoning is undermined--meaning granting the evidence as true, if negate the answer choice, does that wreck the connection between the premise and the conclusion.

Hope that helps!