Conditional reasoning q that should be easy but isn't Forum

[Blahh_Blahh]

Statement: "According to the rules of the university's housing lottery, the only students guaranteed dormitory rooms are fourth-year students."

I diagrammed this: GDR --> FYS

As in, if you are guaranteed a dormitory room, you are a fourth-year student.

But my powerscore materials say it should be diagrammed as FYS --> GDR.

This doesn't make any sense to me, because I think there could be some fourth-year students who AREN'T guaranteed dormitory rooms. Anyway, could somebody please explain why it is diagrammed in that way? This is driving me nuts.

[kaiser]

I'm almost certain you have it right. "The only" is a tricky term, and it indicates a sufficient condition (as opposed to the word "only" on its own, which would indicate a necessary condition). So you have it right.

Here is an example to show that you are right:

The only people in this room are doctors

In that phrase, I know something about every single person in this room (since the term "the only" tells me that we are completely inclusive of everyone in the room). And what do we know about them? That they are all doctors. Does that mean that all doctors are in the room? Of course not. "The only" indicates a sufficient condition, so you are right.

Edit: However, the original phrase is made to sound like those that are guaranteed housing and "4th year students" are perfectly overlapping groups (i.e. different from my doctor example). But if that were the case, it would be biconditional anyway, and you would still be right (since, if A and B are biconditional, then both A --> B and B --> A are correct statements)

[jamesireland]

I would say that an alternate way to put this, in english, would be "ALL students guaranteed dormitory rooms are fourth-year students."

This seems identical in meaning to the original statement, and is clearly diagrammed as you say, GDR --> FYS

[Blahh_Blahh]

Yes, that is exactly what I thought! But then, that would mean PowerScore is just flat-out wrong in this case.... Which makes me a little worried about the value of the class I am currently taking... Oh well.

[kaiser]

I would say that an alternate way to put this, in english, would be "ALL students guaranteed dormitory rooms are fourth-year students."

This seems identical in meaning to the original statement, and is clearly diagrammed as you say, GDR --> FYS

+1

And just to make it extra clear, I always add in my own terms to make "the only" even more clear. I always say to myself "The only [so and so] IN EXISTENCE..." By adding in such forceful words, it always reminds that we are talking about all members of a group/class of things, etc.

[bleern031]

tag

[kaiser]

tag

Lol, I don't think thats too necessary. Here is the whole thread in 3 words that are hard to forget:

The only = Sufficient

/thread

[TIKITEMBO]

.

[notaznguy]

What you diagrammed is correct. If your PS material explicitly said it should have been "If 4th year student,, then you are guaranteed dorm," then that is wrong.

[notaznguy]

What people are saying here is not correct and no, the advice given to countless lsat students is not incorrect nor has it failed them on the numerous lsat tests its been used on I'm not sure what this talk is about only=sufficient. I always associate "only" with the necessary clause. The word "only" itself should be an indicator of something that is necessary to make something included in a group. What the conditional reasoning example is saying is exactly what you were confused about: If you are guaranteed a room, you are a fourth year student. There is nothing else here to indicate that any other students should be considered as being guaranteed a room. Only=necessary, not sufficient.

"only" triggers a necessary condition. "THE only" however, triggers a sufficient condition. Don't ask me why, it's just how it is. That's what it says in the PowerScore LR Bible and that's what Testmasters taught me.

[Bobeo]

"The only students guaranteed dormitory rooms are fourth-year students."
GDR -> FYS

"Only students guaranteed dormitory rooms are fourth year students."
FYS -> GDR

So weird.

[NC1]

Statement: "According to the rules of the university's housing lottery, the only students guaranteed dormitory rooms are fourth-year students."

I diagrammed this: GDR --> FYS

As in, if you are guaranteed a dormitory room, you are a fourth-year student.

But my powerscore materials say it should be diagrammed as FYS --> GDR.

This doesn't make any sense to me, because I think there could be some fourth-year students who AREN'T guaranteed dormitory rooms. Anyway, could somebody please explain why it is diagrammed in that way? This is driving me nuts.

This is why I never diagrammed. The way you explained it is the way I would explain things to myself in my head and I did fine. I didn't diagram a single time on the LSAT in October last year and I can't point out a single answer I got wrong due to not diagramming.

[Jeffort]

Blahh_Blahh,

Is the example you gave from an actual LSAT question or is it from a drill in the Powerscore materials?

It would be great if you could give a reference, I'd like to look at it. If it's in a drill in the LRB, just give chapter and/or page#, if it's from a real LR question, PT#, section and Q#

The word only is a tricky little devil and every single word and phrase surrounding it matters for proper logical interpretation, hence why it is littered all over every LSAT. LSAC and LSs place a lot of weight on critical reading and thinking skills.

I'll comment more if I can see the full sentence verbatim and the context it is used in.

[suspicious android]

Would really love to see a cite for this with a page number to confirm it is actually how the OP quoted it. The last time we got in a similar situation the OP incorrectly paraphrased the source material causing 2-3 pages of hilarious confusion.

Oh, and yeah, like others have already said, it should be:

guaranteed dorm room ---> forth year student

[kaiser]

What people are saying here is not correct and no, the advice given to countless lsat students is not incorrect nor has it failed them on the numerous lsat tests its been used on I'm not sure what this talk is about only=sufficient. I always associate "only" with the necessary clause. The word "only" itself should be an indicator of something that is necessary to make something included in a group. What the conditional reasoning example is saying is exactly what you were confused about: If you are guaranteed a room, you are a fourth year student. There is nothing else here to indicate that any other students should be considered as being guaranteed a room. Only=necessary, not sufficient.

Someone needs to read a little bit closer. Of course only = necessary. No one would argue to the contrary of that. But the trick is that "THE only" = sufficient. Its the word "the" that creates the confusion, since, as you mentioned above, "only" on its own is a necessary indicator word

[Blahh_Blahh]

It's from the PowerScore class books. Lesson 2 homework. Page 2-63. Question 8.

Aren't all of PowerScore's questions real LSAT questions?

I don't know what test number it comes from, since it's just part of a homework drill regarding Mistaken Negation, Mistaken Reversal, and Contrapositive LR questions.

[UofO]

The word "only", in this context, refers to 4th year students; thus, 4th year students becomes the necessary condition in this statement.

That is, if you are guaranteed a dorm room, you must be a 4th year student. You shouldn't just look for words that indicate necessary/sufficient conditions without examining the context in which it is used.

[bp shinners]

tag

Lol, I don't think thats too necessary. Here is the whole thread in 3 words that are hard to forget:

The only = Sufficient

/thread

So glad that this is finally becoming common knowledge.

[upside11]

Ok. Thanks guys . What about the powerscore diagram originally in question? Does anyone know yet if it is correct? I do believe that it is correct based upon what is the necessary part of the conditional and the sufficient part of the conditional but I may be wrong?

[suspicious android]

By the way, for anyone who is interested, this sentence comes from test #47, section 3, question 3.

In summary, if a necessary condition is immediately preceded by “the only”, that condition is both necessary and sufficient.

Wow, I was pretty taken aback by this post, at first when I saw so much text I just skimmed, assuming anyone putting in that much analysis would have gotten it right. No offense, but you gotta think this one over again. Even your primary example doesn't make sense. "The only way he can play is if he is tall?" You're saying that means:

Tall <--> play basketball

So if he's tall, but he's paralyzed?

Sometimes, "the only" can introduce a particular sufficient condition that is also necessary. That doesn't allow us to infer "the only" to be a biconditional indicator. There are many, many, many situations in which it does not refer to a necessary condition.

The only way you will win the race is to practice hard.
So if you practice hard you will win the race? No. That's not what that sentence means.

The only people who eat oranges everyday live in Florida.
So if you live in Florida you eat oranges everyday? No. That's not what that sentence means.

The only girls at the picnic were blond.
So if you are blond you were a girl at the picnic? No. That's not what that sentence means.


Edit: By the way, if this idea had not come from the great, wise, infallable PS Bible, I wonder if anyone would have argued for the "the only" = necessary idea. I see so many posts on this forum that basically say "xyz is true, I read it on page 46 of the PS Bible." So ironic that a book that teaches critical reasoning (and does a pretty good job at it) engenders so much uncritical acceptance.

[kaiser]

By the way, for anyone who is interested, this sentence comes from test #47, section 3, question 3.

In summary, if a necessary condition is immediately preceded by “the only”, that condition is both necessary and sufficient.

Wow, I was pretty taken aback by this post, at first when I saw so much text I just skimmed, assuming anyone putting in that much analysis would have gotten it right. No offense, but you gotta think this one over again. Even your primary example doesn't make sense. "The only way he can play is if he is tall?" You're saying that means:

Tall <--> play basketball

So if he's tall, but he's paralyzed?

Sometimes, "the only" can introduce a particular sufficient condition that is also necessary. That doesn't allow us to infer "the only" to be a biconditional indicator. There are many, many, many situations in which it does not refer to a necessary condition.

The only way you will win the race is to practice hard.
So if you practice hard you will win the race? No. That's not what that sentence means.

The only people who eat oranges everyday live in Florida.
So if you live in Florida you eat oranges everyday? No. That's not what that sentence means.

The only girls at the picnic were blond.
So if you are blond you were a girl at the picnic? No. That's not what that sentence means.

+1 to everything here

Upside11's analysis is quite a bit off, and suggests that "the only" would indicate a biconditional relationship, but that simply isn't the case (its not entirely precluded, but its not something we can infer)

Again, this whole thread can be boiled down to this:

"the only" = sufficient

The post above provides many solid examples of why "the only" only allows us to concretely infer that it indicates a sufficient condition. My example from earlier in this post stresses the same point:

"The only people in the room are doctors"

So every person in the room is a doctor. But it would be ridiculous so think that, because one is a doctor, they must be in the room. Not biconditional at all, and I hope the prospective test-takers realize that this is a deceptively easy concept that they shouldn't overthink.