## Differences between if only and only if

Prepare for the LSAT or discuss it with others in this forum.
Woods

Posts: 59
Joined: Wed Mar 28, 2012 2:13 am

### Differences between if only and only if

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

kaiser

Posts: 2878
Joined: Mon May 09, 2011 11:34 pm

### Re: Differences between if only and only if

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

Br3v

Posts: 4272
Joined: Mon Jun 13, 2011 7:18 pm

### Re: Differences between if only and only if

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: 2878
Joined: Mon May 09, 2011 11:34 pm

### Re: Differences between if only and only if

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.

timmydoeslsat

Posts: 148
Joined: Wed Aug 03, 2011 2:07 pm

### Re: Differences between if only and only if

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: 2878
Joined: Mon May 09, 2011 11:34 pm

### Re: Differences between if only and only if

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

dowu

Posts: 8300
Joined: Wed Mar 28, 2012 9:47 pm