text: A statement is called biconditional when it expresses the idea that the presence of some property is a necessary and sufficient condition for the presence of some other property. Such a statement is usually phrased in the terms "P, if and only if Q." The phrase "if and only if" is often abbreviated as iff. Thus:\n\n    He will be president if and only if he wins the presidential election.\n\n...is a biconditional statement. It is unusual that people use statements with such precision in ordinary language, but they are vital in philosophy and mathematics. The label biconditional arises from the fact that the statement "p iff q" is really an abbreviated way of saying two conditional statements: "if p then q" and "if q then p." Thus, the above biconditional really means:\n\nIf he wins the election, he will be president, and if he is president, he has won the election.