If and only if is an important logical concept, useful in many contexts, both mathematical and nonmathematical. Unfortunately, "if and only if" is also an unwieldy five-syllable phrase. Mathematicians have solved this problem by shortening it to "iff". Unfortunately, this shortening has not caught on in non-mathematical contexts. This makes some communication and thinking unwieldy and ambiguous.

I think the reason "iff" hasn't caught on more broadly is because it's easily misread as "if", and doesn't have an intuitive pronunciation. I think both of these problems would be solved by changing the spelling to "ifeff" (prononunced /ɪfɛff/). The etymology is that you take "iff", and pronounce the second "f" separately. This would slightly improve the thinking and communication of most English speakers.

I think a small group of people using "ifeff" in their writing would likely start a process where "ifeff" eventually takes over, via the usual process by which vocabulary spreads, and that "ifeff" would be used by groups that don't currently have a short-enough word for this concept. I also think the correspondence between "iff" and "ifeff" is intuitive enough that this will not cause very much confusion.

New Comment
21 comments, sorted by Click to highlight new comments since: Today at 10:14 PM

I appreciate "ifeff" due to its continuity with "iff". However, just to add, I've always had a soft spot for the use of just when to mean "if and only if". It is short and elegant and conveys approximately the right meaning even when it isn't recognized as a term of art.

Counter: the reason "iff" works is because people who don't get it can still read the sentence and not worry they missed something key. If you use "ifeff" then massive audiences will infer that the sentence is unreadable.

But they did miss something key!

I'd argue that people who are not familiar with "iff" are usually unfamiliar with its full version "if and only if" as well and, unaware of the need for such distinction, tend to treat regular "if" as bidirectional. These two mistakes will cancel each other out and they won't miss said something key.

Agreed. I think this basically makes concerns about "iff" being mistaken for "if" irrelevant and trying to make a better shorthand for "if and only if" is a distraction with insufficient impact for most anyone to trouble themselves with.

What about "if(f)"? Pronounced 'ifeff', but spelled 'if(f)' so it's both:

  1. Easy to tell that this is a variant of 'if', and if you round things off to colloquial 'if' then you'll at least sort of get what's being said (context probably helps).
  2. Easy to tell that it's not just 'if' or a typo for 'if'.

I wouldn't expect if(f) to be linguistically successful; it's weird in a not-quite-a-word way that means it can't ever become a regular vocabulary item.

Alt: I think ifif makes much more sense than ifeff. It's super unclear where the 'e' comes from or why there's two 'f's, but "if and only if" is "ifif" if you take the start and the end.

How about if'f or if-f? Both are easier to type than if(f), but still look less like an error than iff.

The whole "add punctuation" strategy still ruins the word for Scrabble, though. :(

Edit: ... and I see now that gilch had the exact same idea right below.

How about if'f or if-f?

I think the reason "iff" hasn't caught on more broadly is because it's easily misread as "if"

Also, if you aren't familiar with "iff" you might see it and assume it's just a typo for "if". Jargon catches on better if it's obviously jargon, so people can google it or ask questions when they notice they don't understand.

Why 'ifeff', though? I'm not seeing a logical connection between the '-eff' and '... and only if'. I'd have expected the best shorthand to look more connected to the original, like 'iffo'.

"Eff" is the pronounciation of the letter f, so iff becomes if-f becomes if-eff. It might be more intuitive with a dash, but also it's less like a word. I'll edit in an explanation of the etymology; I thought it was more intuitive than it actually was.

Ahh, OK. This has the advantage that it's connected to 'iff', so you're competing less with existing usage.

What about "if-if"? Short, obviously not a typo, intuitive spelling. Oh, seems like stutter.

Logicians still can't agree whether the symbol for if and only if should be a triple bar or a double arrow. Odds that they'd all sign up for this, rather than having it be, at best, yet another competing standard, seem low.

I don't see what's wrong with having competing standards in this situation

FBI doesn't need to be EfbiAi to be workable. Ifeff mixes acronyms on proper words. "sif" meaning "strictly if" would fit my aesthetics better and would be analogous how "greater than" has the versions "strictly greater" and "greater or equal"

An interesting  idea. It would definitely need to be explained, but it is very easy to see and understand after that [though it is also a Norse God.] Perhaps it should be tried mainly in the longer form at first, for people to get used to it, replacing the phrase 'if and only if'.

I see a major problem here, which is all the worse for simplicity. It sounds like a censored swear word. The types that would actually use this in the beginning are being technical, and it isn't very technical to be swearing about if and only if [publicly]. It sounds more appropriate for a rant. The current implementation has problems, but 'iff' is clearly superior to the proposed alternative.

If you actually succeeded and everyone started writing "ifeff" the etymology would no longer point to a logical story.

"Ifof" seems better to me. It more resembles "If and only if" which would make it easier to learn.