Metaphysics is a philosophical area of study which concerns itself with the existence of things. Are things real? Or, do they exist simply in ones mind? Is the mind real? These are some of the elementary questions that come to one who inquires into the nature and ultimate significance of the universe. Those who hold reality subsists only in thought, are idealists (idealism); those who hold reality subsists in only matter, are realists or materialists (materialism); and those who hold that reality subsists both in thought and in matter, are dualists (dualism).