I need help diagramming these two statements: Forum

[I<3ScholarlySweets!]

(1) I only bake on Mondays.

Do you diagram it as: Bake --> Mondays, or Mondays --> Bake. Is the "I only" the same as "the only" and therefore a sufficient indicator? I find this statement confusing because "on" is a sufficient indicator, so what follows after "on" (i.e. Mondays) should be the sufficient, right?

(2) Bart will only shave if Amy likes him.

Do you diagram it as: Bartshaves --> Amylikes, or Amylikes --> Bartshaves. Clearly what follows after "if" is the sufficient, and what follows after "only" is necessary, so Bartshaves --> Amylikes would be credited. However, in The LSAT Trainer, on page 460 in Lesson 31, the statement "...and Leon will only attend if Sarah does not" is diagrammed as: Leonattends --> Sarahdoesnot.

[gatesome]

(1) I only bake on Mondays.

You bake only if it is Monday. Therefore, IF you bake, THEN it is Monday.

Bake --> Monday

(2) Bart will only shave if Amy likes him.

Bart may or may not shave, but IF Bart shaves, THEN Amy likes him.

BartShaves --> AmyLikes

[I<3ScholarlySweets!]

thanks, gatesome. Can you explain (2)?

[gatesome]

thanks, gatesome. Can you explain (2)?

(2) Bart will only shave if Amy likes him.

There are two possible cases of Bart shaving:

1) Bart shaves.
2) Bart does not shave.

Similary, there are two possible cases of Amy liking Bart:

A) Amy likes Bart.
B) Any does not like bart.

As we know from basic math, 2*2=4. There are 4 possible scenarios here:

a) Bart shaves. Amy likes Bart.
b) Bart shaves. Amy does not like Bart.
c) Bart does not shave. Amy likes Bart.
d) Bart does not shave. Amy does not like Bart.

Compare each scenario to the rule: (2) Bart will only shave if Amy likes him.

a) OK (works fine) !!
b) Contradiction!
c) Fails Sufficient (because Bart does not shave, the rule does not apply)
d) Fails Sufficient

We know from this that any time Bart shaves, Amy must like Bart. We can translate this as:

IF Bartshaves THEN AmyLikes
Bartshaves --> AmyLikes

[TheodoreKGB]

.

[PeanutsNJam]

This is completely opposite. It should translate: Amy Likes ----> Bart Shaves. How do I know for sure? "If" ALWAYS introduces the sufficient condition. "Will" and "Only" ALWAYS introduce the necessary condition. Check out 7Sage for logic explanations; they're awesome!

Yeah, "only" introduces necessary... Bart will only shave if Amy like him... so Amy liking him is necessary... so it's Bart shaves -> Amy likes.

[gatesome]

This is completely opposite. It should translate: Amy Likes ----> Bart Shaves. How do I know for sure? "If" ALWAYS introduces the sufficient condition. "Will" and "Only" ALWAYS introduce the necessary condition. Check out 7Sage for logic explanations; they're awesome!

We are dealing with an "ONLY IF," not an "IF"

A if B means that B implies A.
A only if B means that A implies B

This is completely opposite. It should translate: Amy Likes ----> Bart Shaves. How do I know for sure? "If" ALWAYS introduces the sufficient condition. "Will" and "Only" ALWAYS introduce the necessary condition. Check out 7Sage for logic explanations; they're awesome!

Yeah, "only" introduces necessary... Bart will only shave if Amy like him... so Amy liking him is necessary... so it's Bart shaves -> Amy likes.

For clarity, you are agreeing with me and disagreeing with TheodoreKGB.

[gatesome]

This is completely opposite. It should translate: Amy Likes ----> Bart Shaves. How do I know for sure? "If" ALWAYS introduces the sufficient condition. "Will" and "Only" ALWAYS introduce the necessary condition. Check out 7Sage for logic explanations; they're awesome!

Consider the following counter example:

Amy likes Bart, but Bart does not know, because Amy is very shy.
Bart, thinking that life is hopeless because he doesn't know Amy likes him, neglects his appearance and refuses to shave.

^ In this scenario, Amy likes = TRUE; Bart shaves = FALSE

Amy Likes ----> Bart Shaves is contradicted.

[I<3ScholarlySweets!]

Hey gatesome, thanks for your posts. But I'm still not sure how "Bart will only shave if Amy likes him" is an ONLY IF statement. I would understand if it were worded as "Bart will shave ONLY IF Amy likes him." Here, it is clear that we are dealing with an ONLY IF statement (cause only and if are together and there aren't any words between them). But in "Bart will only shave if Amy likes him," the word "shave" is in between "only" and "if" so I simply think of putting everything after "if" in the sufficient, and the rest in the necessary. I do this because I've been told that if is a sufficient indicator and whatever comes after it is sufficient.

[PeanutsNJam]

Scholarly,

I will only get drunk if I drink alcohol

and

I will get drunk only if I drink alcohol

are the same statements.

[gatesome]

Hey gatesome, thanks for your posts. But I'm still not sure how "Bart will only shave if Amy likes him" is an ONLY IF statement. I would understand if it were worded as "Bart will shave ONLY IF Amy likes him." Here, it is clear that we are dealing with an ONLY IF statement (cause only and if are together and there aren't any words between them). But in "Bart will only shave if Amy likes him," the word "shave" is in between "only" and "if" so I simply think of putting everything after "if" in the sufficient, and the rest in the necessary. I do this because I've been told that if is a sufficient indicator and whatever comes after it is sufficient.

Bart will ONLY shave IF Amy likes him. == Bart will shave ONLY IF Amy likes him.

The two statements are identical.

[PeanutsNJam]

More examples:

I will only go to YLS if they have hot girls. If I go to YLS, they must have hot girls.

I will only buy a helicopter if I can afford it. If I bought a helicopter, I was able to afford it.

I will only use a mac if hell freezes over. If I'm using a mac, then hell must have frozen over.

[anonygate]

Found this on LSATMax:

-Sally will only be able to go out tonight if she can complete all of her homework.

The trick to an “only” is to put the arrow through the only so that whatever follows the “only” is the necessary condition, and whatever precedes the “only” is the sufficient condition. The above statement written in “if/then” form would be: “If she can complete all of her homework, then Sally will be able to go out tonight.” Let’s diagram:

CAHW ==> GOT

Contrapositive:

not GOT ==> not CAHW

Remember that an “only” is not the same as “the only.” The words “the only” will introduce a sufficient condition. Let’s give that a try:

-The only way that Sally will be able to go out tonight is for her to do her homework.

Again, “the only” introduces the sufficient condition. The rest of the sentence is the necessary condition. The “if/then” form of this sentence is: “If Sally is able to go out tonight, then she has done her homework.” Let’s diagram:

GOT ==> DHW

Contrapositive:

not DHW ==> not GOT

link: http://lsatmax.com/lsat-prep-sufficient ... tatements/

Judging by the responses in this thread, these answers seem wrong. Help?

[anonygate]

Bump. ^this has me trippin'. Are all the responses here consistent with each other? Please advise

[Christine (MLSAT)]

Found this on LSATMax:

-Sally will only be able to go out tonight if she can complete all of her homework.

The trick to an “only” is to put the arrow through the only so that whatever follows the “only” is the necessary condition, and whatever precedes the “only” is the sufficient condition. The above statement written in “if/then” form would be: “If she can complete all of her homework, then Sally will be able to go out tonight.” Let’s diagram:

CAHW ==> GOT

Contrapositive:

not GOT ==> not CAHW

<snip>

link: http://lsatmax.com/lsat-prep-sufficient ... tatements/

Judging by the responses in this thread, these answers seem wrong. Help?

Wow, yeah, that first example is completely incorrect.

"Sally will only be able to go out tonight if she can complete all of her homework."

You can't just look at the word "only" and ignore everything else in the sentence. We don't simply have "only", we have a separated "only if" statement. THAT "only if" is the 'arrow', or 'then', or 'necessary', and it's introducing the completing of homework.

This would be diagrammed as:
GOT --> CAHW


That website is utterly, blatantly, and completely incorrect.

[anonygate]

Found this on LSATMax:

-Sally will only be able to go out tonight if she can complete all of her homework.

The trick to an “only” is to put the arrow through the only so that whatever follows the “only” is the necessary condition, and whatever precedes the “only” is the sufficient condition. The above statement written in “if/then” form would be: “If she can complete all of her homework, then Sally will be able to go out tonight.” Let’s diagram:

CAHW ==> GOT

Contrapositive:

not GOT ==> not CAHW

<snip>

link: http://lsatmax.com/lsat-prep-sufficient ... tatements/

Judging by the responses in this thread, these answers seem wrong. Help?

Wow, yeah, that first example is completely incorrect.

"Sally will only be able to go out tonight if she can complete all of her homework."

You can't just look at the word "only" and ignore everything else in the sentence. We don't simply have "only", we have a separated "only if" statement. THAT "only if" is the 'arrow', or 'then', or 'necessary', and it's introducing the completing of homework.

This would be diagrammed as:
GOT --> CAHW


That website is utterly, blatantly, and completely incorrect.

Thanks.

That's a shame. I met the guy who founded that prep company. He scored a 174 and went to Harvard Law.

What about the second example?

"The only way that Sally will be able to go out tonight is for her to do her homework."

[I<3ScholarlySweets!]

Bump. ^this has me trippin'. Are all the responses here consistent with each other? Please advise

yeah, this construction is really confusing, if not the MOST confusing.