Grouping/Linear Combination Setup Practice Drill #3

[yongjook]

Drill #3 contains the condition that states "If I is not interviewed then R must be interviewed", which is translated to not I not R.
On page.348 it says I or R is always interview and possibly both are interviewed. Yet in the diagram I/R is written. Does this mean we should simply keep in mind that both I and R can be interviewed?

[Nikki Siclunov]

Hi yongjook,

The statement in question contains a negative sufficient condition, whereby the absence of an event or an occurrence is the sufficient condition that triggers the conditional relationship:

NOT I R
NOT R I

So, whenever one of these two is not interviewed, the other one must be interviewed. It's impossible, therefore, to interview no one: either I or R must be interviewed. This fact alone does not preclude the possibility of both being interviewed: in logic, the correlative conjunction "either/or" is inclusive unless indicated otherwise (e.g. "either/or, but not both"). In this case, there is nothing stopping both I and R from being interviewed at the same time, as we don't know what must be true if either one of them is interviewed (to conclude otherwise would be a MR/MN of the original rule):

I ?
R ?

There are several other ways to convey the same type of relationship. Take a look:

Either I or R must be interviewed.
At least one of I or R must be interviewed.
At most one of I or R cannot be interviewed.

To answer your other question, your representation of this rule is correct, albeit it's a bit too complicated for my taste:

NOT I NOT R

Literally, this means, "If I is not interviewed, it cannot be true that R is not interviewed" (and vice versa). Personally, I just wouldn't use the Double-Not arrow to represent this relationship, as you end up with way too many negations that are difficult to keep track.

Hope this helps!

[DlarehAtsok]

I have a problem with the rule "Q is interviewed, and must be interviewed earlier than K and R if either are interviewed." This is a two-part rule, the first part is easy and just entails that Q must be selected. The second part is conditional and states if K or R is in, Q must be before both. Does this entail that if K or R is in, the other must also be in, otherwise how would Q be before both?

Thanks!

[Claire Horan]

Hi Dlareh,

This is indeed a confusing rule. The Logic Bible interprets this rule as meaning Q has to be before any of R or K that is included, but not the extra inference that you made, that R K.

Rather than defend that interpretation versus your own, I'll offer some practical, forward-looking advice:

When you run into two possible interpretations and you really aren't sure which is intended, choose the interpretation with the narrowest effect (smallest impact) to avoid making unwarranted assumptions.

So, here, the two possible interpretations are that 1) Q has to be before K, if selected, and before R, if selected; or 2) if K or R is included, both must be. Since (1) is narrower, I should take that interpretation because if I am wrong, it just means I wouldn't use a helpful clue--it wouldn't cause me to get answers wrong. Then, as you move through the questions, sometimes you realize that one of the two interpretations is the right one.

[leslie7]

for the third rule, I didn't get that Q is interviewed and is added to the interview selection group even though I diagrammed correctly ...

K or R -> Q --- K and or Q---R

since K or R triggers Q before K or R then I thought K or R had to be present to trigger Q but I think I realize now that it wasn't triggering Q it was triggering the sequence of Q before K or R, is that right?

Also if that is the case what is the contrapositive of this (I think i'm picking up a pattern of diagraming and understanding what the negation of sequencing rules looks like and what it really means in practice)

so this would be?

Not Q before K or Not Q before R --> Not K and Not R?

What does this mean in practice? Does it mean that if you have Q after K or R you do not have K and you do not have R? (sorry)

[leslie7]

picking up a pattern of not understanding the negation of sequencing rules ***

I did get all of these correct by the way so I am making a lot of progress, thanks to you guys

[Dave Killoran]

Hi Leslie,

Just to keep the forum orderly, I'm going to have your question appended on to the end of the main discussion of this item at: viewtopic.php?f=1350&t=7489

The third rule is--by design--an unusual one (we want you to encounter odd rules since the LSAT likes to throw them at test takers occasionally!). Part of the oddness is in the first phrase, "Q is interviewed." This is a separate fact from the remainder of the rule, and it means Q is always in your group of 5 (as you rightly noted). The contrapositive of this rule starts with the negation of that necessary condition (Q is NOT interviewed earlier than K or R) but for that to happen, it would mean that neither K or nor R are there, so we won't ever see an arrangement where K or R is actually earlier than Q; K and R simply won't be in the group at all. Strange, right?

So, ultimately, what's happening is that once we know Q is in the group for sure, you are then just looking for K or R or both, and if they appear, they are after Q.

Well done on getting this right!

Thanks!