from The American Heritage® Dictionary of the English Language, 4th Edition

  • abbr. if and only if

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • abbr. if and only if; used to show that the predicate that follows it has the same truth value as the predicate that precedes it.


Sorry, no etymologies found.


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  • Interesting to see widespread use of this bit of philosophical jargon on the Twitter.

    Who said Twitter was an intellectual desert?

    October 1, 2011

  • I will iif you will.

    October 1, 2011

  • I do! I do want to do that sort of thing!

    And unless I'm mistaken, your statement works out as "true". :-)

    May 9, 2008

  • Trouble is, trying to pronounce it without making it confusible with if can be a bit iffy.

    Then again, it means one can write things like 'If "if P then (Q iff R)" is a wff iff "if (if P then Q) iff R" is a wff, then iff "iff P then (Q iff R)" is a wff, if "P iff (Q iff R)" is a wff, "(P iff Q) iff R" is a wff'.

    Just in case you wanted to do that sort of thing.

    May 8, 2008

  • I like this word. It makes me feel nostalgic, because I saw a lot of it back in college when I was getting my philosophy degree.

    May 8, 2008

  • "If and only if."

    May 7, 2008