parsing

[commandercranky]

Is there a difference between "if" and "if and only if"?

If you think so, please explain.

Comments

lawyer grammar queen

[bing_crosby]

emphasis only, I would think. And let me test this out-- like "or" vs "and/or," it's more vague than the shorter version while claiming to be more specific.

Re: lawyer grammar queen

[commandercranky]

I wasn't sure when I posted this, but I've thought about it more and I think there is an important difference. I disagree that the longer version is vague. It's the shorter version that is less specific.

For example (to borrow from vampyrecat), imagine two different rules:

1. If you clean your room you get a cookie.

2. If and only if you clean your room you get a cookie.

Under rule 1 there might be other ways to get a cookie, but we know this is one way. Under rule 2 you're stuck - you better clean your room if you want a cookie, because there's no other option.

Re: lawyer grammar queen

[bing_crosby]

ok, point taken. didn't take much.

Re: lawyer grammar queen

[i_am_electro]

As someone who thinks like a robot sometimes, you are correct. If and only if is very important when trying to limit cookie distribution.

[pomo_drunkard]

Yes.

"If and only if" means that certain things absolutely _must_ happen for there to be a certain outcome. "If" doesn't have that limitation.

It's a certain amount of emphasis, practically.

Of course, Wikipedia says it better than I can.

[vampyrecat]

There is a huge difference.

If x=30 then you get a cookie.
If x=40 then you also get a cookie.

If and only if y=40 you get a pie.

[commandercranky]

Yeah, thats similar to what I worked out after I posted this, but I left it up to hear how else people interpret it.

[vampyrecat]

I derived that interpretation from the world of computer programming. I like to borrow programming algorithms for legal arguments.

[saltbox]

It's different enough that philosophers use the term "iff" for "if and only if"! (I just learned about "iff" the other day. Hunh!)

[raccoonpower]

IF AND ONLY IF is more emphatic--and hostile--and disallows any other options. says me.

[ketzie]

I agree that it disallows other options, but that's the point--precision. In my world (cs/math), saying that iff is hostile is like saying that 5 is hostile. :-)

SMILES!

[raccoonpower]

gotcha--in CS/math/logic/philosophy world, it's value-neutral and important.

but in my world (as our pal cranky well knows), it's all about tones. i appreciate having hostile linguistic choices available myself...

Re: SMILES!

[ketzie]

Yup. Hostile definitely has its uses.