Differences between if only and only if

Woods
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Joined: Wed Mar 28, 2012 2:13 am

Differences between if only and only if

Postby Woods » Sat May 05, 2012 12:21 am

A, only if B-B is necessary for A.
But what does "A if only B" mean? Thanks!

kaiser
Posts: 2940
Joined: Mon May 09, 2011 11:34 pm

Re: Differences between if only and only if

Postby kaiser » Sat May 05, 2012 12:22 am

.
Last edited by kaiser on Sat May 05, 2012 1:11 am, edited 1 time in total.

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Br3v
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Re: Differences between if only and only if

Postby Br3v » Sat May 05, 2012 12:47 am

Short hand is you kind of flip your arrow around.

Normal if:
A if B
B > A
I will be tired if I run a marathon
If I run a marathon > I will be tired


Only if:
A only if B
A > B

I will be tired only if I run a marathon
If I am tired > then I ran a marathon
We know this because that's the only way you'd be tired!

kaiser
Posts: 2940
Joined: Mon May 09, 2011 11:34 pm

Re: Differences between if only and only if

Postby kaiser » Sat May 05, 2012 12:49 am

Br3v wrote:Short hand is you kind of flip your arrow around.

Normal if:
A if B
B > A
I will be tired if I run a marathon
If I run a marathon > I will be tired


Only if:
A only if B
A > B

I will be tired only if I run a marathon
If I am tired > then I ran a marathon
We know this because that's the only way you'd be tired!


His question was about the phrasing "if only" (as in "A if only B"), which is certainly odd, and I can't recall ever seeing it used on the LSAT.

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timmydoeslsat
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Re: Differences between if only and only if

Postby timmydoeslsat » Sat May 05, 2012 1:08 am

The phrase "if only" is a sufficient condition.

If only I had enough money, I would go to the beach.

Enough money ---> Beach

Only if = necessary.

If only = sufficient. No different than regular if.

kaiser
Posts: 2940
Joined: Mon May 09, 2011 11:34 pm

Re: Differences between if only and only if

Postby kaiser » Sat May 05, 2012 1:11 am

timmydoeslsat wrote:The phrase "if only" is a sufficient condition.

If only I had enough money, I would go to the beach.

Enough money ---> Beach

Only if = necessary.

If only = sufficient. No different than regular if.



After thinking it over, I think this is correct, and my initial intuition was wrong. OP, disregard my earlier post

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dowu
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Re: Differences between if only and only if

Postby dowu » Mon May 07, 2012 3:56 pm

:shock: :shock:




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