 The sections above considered some of the basic ideas that fed into the creation of model theory, noting some ways in which these ideas appeared either in mathematical model theory or in other disciplines that made use of model theory.  None of this is particularly philosophical, except in the broad sense that philosophers work with ideas.  But as mathematical model theory has become more familiar to philosophers, it has increasingly become a source of material for philosophical questions.  In 2018 two books appeared that directly addressed this philosophical use of model theory, though in very different ways.