In logic and related fields such as mathematics and philosophy, if and only if (shortened iff) is a biconditional logical connective between statements.In that it is biconditional, the connective can be likened to the standard material conditional ("only if", equal to "if ... then") combined with its reverse ("if"); hence the name. The result is that the truth of either one of the connected statements requires the truth of the other (i.e. either both statements are true, or both are false).