# A if, but only if, B

#### finessll

##### A if, but only if, B
« on: May 26, 2009, 05:23:03 PM »
the rule  'a if, but only if, b' was recently tested on the games section ... i didn't fully understand the rule, and given the time constraints i didn't have the luxury to stop and think about it, so i took a gamble and assumed that rule implied both 'if a then b' and 'if b then a' ... luckily, i guessed right but i never want to do this on a real LSAT

i know that 'a if, and only if, b' implies 'if a then b' as well as 'if b then a' ... so i understand this relationship ... i just don't get why 'but' in the example above has the same effect as 'and' in this example ... any insights would be helpful

here are my thoughts ... in 'a if, and only if, b' makes sense because it's both 'a if b ... if b then a' and 'a only if b ... if a then b' ... can someone break 'a if, but only if, b' down for me like that? Thanks!

#### gzl

##### Re: A if, but only if, B
« Reply #1 on: May 26, 2009, 06:07:24 PM »

here are my thoughts ... in 'a if, and only if, b' makes sense because it's both 'a if b ... if b then a' and 'a only if b ... if a then b' ... can someone break 'a if, but only if, b' down for me like that? Thanks!

Think of "but" as just giving the contrapositive of "and". "if not b then not a"

#### finessll

##### Re: A if, but only if, B
« Reply #2 on: May 26, 2009, 06:21:10 PM »
thanks gonzolaw, that's a great tip! it clarifies it a lot more ...

here's a link to what i was discussing what other folks but your tip definitely crystallizes the difference in wording ... http://www.top-law-schools.com/forums/viewtopic.php?f=6&t=73348&p=1655601#p1655601

#### .5L

##### Re: A if, but only if, B
« Reply #3 on: May 27, 2009, 01:12:40 AM »
Understand the difference between the following:

A if B.

This means that if B occurs then A will occur.  But it does not mean that if C occurs then A will not occur, or if D occurs then A will not occur, etc.  In other words, it's possible for A to occur even if B does not occur.

A if, but only if, B.

This means that if B occurs then A will occur. In this situation, though, if C were to occur then A would not occur, and if D were to occur then A would not occur, etc. In other words, it is not possible for A to occur if B does not occur.

I think OP was more confused about why "but" and "and" should be read as equivalent.

#### EarlCat

• 2080
• i'm in ur LSAT blowin' ur curve
##### Re: A if, but only if, B
« Reply #4 on: May 29, 2009, 09:19:18 PM »
"But" means "and."

#### Julie Fern

• 25797
• hillary clinton say "boo!"
##### Re: A if, but only if, B
« Reply #5 on: May 30, 2009, 03:13:52 AM »
how "/thread"?  there more boxes down here!

#### juile20099

##### Re: A if, but only if, B
« Reply #6 on: June 04, 2009, 04:59:22 AM »
i know that 'a if, and only if, b' implies 'if a then b' as well as 'if b then a' ... so i understand this relationship ... i just don't get why 'but' in the example above has the same effect as 'and' in this example ... any insights would be helpful  here are my thoughts ... in 'a if, and only if, b' makes sense because it's both 'a if b ... if b then a' and 'a only if b ... if a then b' ... can someone break 'a if, but only if, b' down for me like that? Thanks!

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#### Julie Fern

• 25797
• hillary clinton say "boo!"
##### Re: A if, but only if, B
« Reply #7 on: June 04, 2009, 05:02:57 AM »
told ya.

#### Julie Fern

• 25797
• hillary clinton say "boo!"
##### Re: A if, but only if, B
« Reply #8 on: June 04, 2009, 08:00:39 AM »
rhetorically speaking, "but" usually suggest unexpected, much like julie.  here, it just thrown in mess with you.

#### noumena

##### Re: A if, but only if, B
« Reply #9 on: June 06, 2009, 03:50:03 PM »
I think "A if, but only, if B" says something different from "A if and only if B." All "if and only if" statements can be parsed into a conjunction of two stipulations: (keeping your variables) A if B and A only if B (i.e., A as necessary and sufficient conditions, respectively).

It is true that in most semantic contexts, "but" serves to emphasize an otherwise uninteresting conjunction (I studied little and I passed vs. I studied little *but* I passed); in this case, however, the "but," set off in a restrictive relative clause, constrains the meaning. I think in effect, the "but only if" part of the statement "swallows" up and replaces the "if" part of the statement. It is as if the speaker corrected himself mid-sentence.

For instance, if your annoying cousin nagged you about taking him to swim, you might say "okay, if you finish your homework." If you said that, you would be promising to take him to swim once he finished his homework. But you could be sneaky and say "Only if you finish your homework," in which case no promise would have been uttered. I think "A if, but only, if B" approximates this sense more than the former (just repeat the following statements--they do sound like they mean different things: okay, if you finish your homework VS. okay, if, BUT only if, you finish your homework. Otherwise, it's just redundant (why would you say, in normal linguistic contexts, that something is both a necessary and sufficient condition if it is going to be sufficient either way?--it serves only to confuse your poor cousin!).

Having said this, I am not certain, however, if I am right (or if there is a right answer). A if, but only, if B, is not a conventional usage. It's ambiguous, because I have a feeling (going by previous posts) that our intuitions do diverge here. It shouldn't be on the LSAT, IMO. They should stick with the traditional IFF (if and only if) construction. I think we will just have to accept whatever opinion LSAC has about this.

So does anyone who recently took the test know which side they're on?