iff an abbreviation for ‘if and only if’ that is used as if it were a single propositional operator (connective). Another synonym for ‘iff’ is ‘just in case’. The justification for treating ‘iff’ as if it were a single propositional connective is that ‘P if and only if Q’ is elliptical for ‘P if Q, and P only if Q’, and this assertion is logically equivalent to ‘P biconditional Q’. See also BICONDITIONA. R.W.B.