 A formal system is complete if for every statement of the language of the system, either the statement or its negation can be derived (i.e., proved) in the system. A formal system is consistent if there is no statement such that the statement itself and its negation are both derivable in the system. Only consistent systems are of any interest in this context, for it is an elementary fact of logic that in an inconsistent formal system every statement is derivable, and consequently, such a system is trivially complete.