## Quick conditional question

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lawschool2014hopeful

Posts: 554
Joined: Mon Oct 25, 2010 8:48 pm

### Quick conditional question

Hey All,

This is gonna sound silly, but I cant seem to "grasp" the "unless" concept, even though I know how to diagram it.
For example,
R unless T.
The right way is not T-> R
but I cant seem to not get why is it not R -> not T

I tried to use the following example, but i cant seem to convince myself
I swim unless I eat.
Correct: I dont eat-> I swim
Incorrect: I swim -> I dont eat (can someone explain why this is wrong)?

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

jimmierock wrote:R unless T.
The right way is not T-> R
but I cant seem to not get why is it not R -> not T

Actually it's neither.
"R unless T" means that R happens, except in the case where T happens: in that case, R doesn't happen. So you get:
T -> not R
And the contrapositive:
R -> not T

So in the case, "I swim unless I eat"
The correct statement is actually "I eat -> I don't swim"
The contrapositive being "I swim -> I don't eat"

EDIT: Wait, I'm wrong. Am I wrong?

VasaVasori

Posts: 571
Joined: Sun Dec 11, 2011 2:36 pm

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 2 times in total.

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

Wait, "A unless B" is the same as "B unless A" is the same as "A or B"

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

The LSAT is on Monday why is this tripping me up!?

VasaVasori

Posts: 571
Joined: Sun Dec 11, 2011 2:36 pm

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 1 time in total.

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

VasaVasori wrote:
cc.celina wrote:Wait, "A unless B" is the same as "B unless A" is the same as "A or B"

Yea, I think.

A unless B = ~A -> B
B unless A = ~B -> A

Good, ok, I was getting worried there.

So jimmie, to clarify, both "I don't eat -> I swim" and "I dont swim -> I eat" are correct.

All of this can be simplified with the statement "I eat or I swim"

VasaVasori

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Joined: Sun Dec 11, 2011 2:36 pm

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 1 time in total.

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

VasaVasori wrote:NOTE, however, that this doesn't mean that both R and T can't be true together.

Is this true? If R unless T, then doesn't R have to happen in any case T doesn't happen, and in the cases T does happen, R can't happen... meaning either R or T, but not both, is always true? I'm confusing myself

lawschool2014hopeful

Posts: 554
Joined: Mon Oct 25, 2010 8:48 pm

### Re: Quick conditional question

lolol! you guys are confusing me, I am pretty sure I am right because I just got it Dave's videos.

R unless T = ~T -> R

http://www.velocitylsat.com/video/pages ... atements-7
1:42

but i just cant convince myself in a semantically meaningful way that it is.

VasaVasori

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Joined: Sun Dec 11, 2011 2:36 pm

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 4 times in total.

Br3v

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Joined: Mon Jun 13, 2011 7:18 pm

### Re: Quick conditional question

here is the trick:

When you see unless, it introduces the necessary. Now reverse the other part and that is your sufficient.
Ex:
You will get A unless you get B

NOT A > B
Or
NOT B > A

Think about it, you will get A unless you get B, so if you get B then you aren't getting A

Ex 2:
Unless you do not get fired, you will not be able to pay the bill

Take unless for necessary: ( NOT be able pay bill)
Reverse the other for Sufficient: (Get fired)

Get Fired > NOT able to pay bill
Able to pay bill > NOT fired

suspicious android

Posts: 919
Joined: Tue Feb 09, 2010 4:54 pm

### Re: Quick conditional question

Yeah, guys, please stop. Not to be mean, but unless you're really clear on an concept, you shouldn't be offering this kind of advice.

OP gave the contrapositive of the "normal" way to diagram an unless statement, which is fine.

R unless T
~R --> T
~T --> R

all mean the same thing.

As for semantics, it doesn't seem to make sense because in colloquial language, when someone says "I'm going to the store unless it's raining" they mean:

~store --> rain
AND
store --> ~rain

However, the actual meaning of the sentence doesn't necessarily imply that. Imagine a situation like this:

She will die tomorrow unless she gets the antidote.

Can she die tomorrow if she gets the antidote? Sure, what if she gets hit by a bus? The antidote is necessary for her not dying, but the antidote is not sufficient for anything, no one can know what will happen if she gets it.

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

According to LSAC, you CAN have both.

This is so counterintuitive...

Not to be mean, but unless you're really clear on an concept, you shouldn't be offering this kind of advice.

I thought I was crystal but I've successfully managed to confuse myself

VasaVasori

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 1 time in total.

Br3v

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### Re: Quick conditional question

OP I can assure you my above post is correct. Didn't read anyone else's.

suspicious android

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Joined: Tue Feb 09, 2010 4:54 pm

### Re: Quick conditional question

From the original post:

jimmierock wrote:R unless T.
The right way is not T-> R

This is correct.

I swim unless I eat.
Correct: I dont eat-> I swim

This is also correct. VasaVasori and CC are getting confused here. Brev also gave an accurate post.

As to the why it is counterintuitive (I totally agree it is), see the example about the antidote and let me know if it makes sense.

VasaVasori

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Joined: Sun Dec 11, 2011 2:36 pm

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 1 time in total.

cc.celina

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Joined: Fri May 25, 2012 1:17 pm

### Re: Quick conditional question

suspicious android wrote:As to the why it is counterintuitive (I totally agree it is), see the example about the antidote and let me know if it makes sense.

It does, thank you. How I ever managed 180s on PTs without properly understanding this escapes me =/ Sorry for confusing you, guys.

VasaVasori

Posts: 571
Joined: Sun Dec 11, 2011 2:36 pm

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Last edited by VasaVasori on Sat May 02, 2015 10:57 pm, edited 1 time in total.

lawschool2014hopeful

Posts: 554
Joined: Mon Oct 25, 2010 8:48 pm

### Re: Quick conditional question

suspicious android wrote:From the original post:

jimmierock wrote:R unless T.
The right way is not T-> R

This is correct.

I swim unless I eat.
Correct: I dont eat-> I swim

This is also correct. VasaVasori and CC are getting confused here. Brev also gave an accurate post.

As to the why it is counterintuitive (I totally agree it is), see the example about the antidote and let me know if it makes sense.

Yes, thank you, that definitely clean this up a bit. Is just so damn un-intuitive is hard to get it, but I have come up with a method to just diagramming it right.
X unless Y.
Keep x positive (in original format), and negate y.
~Y -> X.

Another example
Not X unless Y
~Y -> ~ X.

Does this system sound it works?

Br3v

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### Re: Quick conditional question

No way that humble brag goes unmentioned.

suspicious android

Posts: 919
Joined: Tue Feb 09, 2010 4:54 pm

### Re: Quick conditional question

VasaVasori wrote:
My posts in this thread are accurate. Every single one. Just sayin'.

Getting defensive up in here.

I'm sorry, you were accurate addressing CC's ideas, but I got confused between what two posters were saying. However, I think you misinterpreted the OP:

The OP diagrammed "R unless T" as ~R -> ~T or R -> ~T (I can't tell because of the placement of his word "not"). This isn't correct: neither is the contrapositive of any other correct form of the answer.

Just a misread of the OP's diagram since he didn't used the ~ marks. OP accurately diagrammed the original "R unless T" as "not T --> R", that is to say "~T --> R".

suspicious android

Posts: 919
Joined: Tue Feb 09, 2010 4:54 pm

### Re: Quick conditional question

X unless Y.
Keep x positive (in original format), and negate y.
~Y -> X.

Another example
Not X unless Y
~Y -> ~ X.

Does this system sound it works?

The way you diagram these makes my head hurt. You can always just change "unless" to "if not" to get the diagrams you do, but I (and I think most people) memorize the formula as "unless introduces the necessary, negate the other part of the statement, that's the sufficient", so ours come out different (but equal).

Helicio

Posts: 482
Joined: Wed Aug 11, 2010 5:22 pm

### Re: Quick conditional question

Maybe making it more concrete will help.

I will not buy an ice cream cone (not A) unless my dad gives me money (B).
(Not A unless B)

If I buy an ice cream cone (A), then my dad gives me money (B).
A--->B

So not A unless B is A--->B.

Another example:

A unless not B means If A does NOT occur, B does NOT occur.

HTH