  Secondly, it characterizes things as material and spatio-temporal entities, that is, as physical objects. Leibniz conceived monads as spiritual concreta. For the later Brentano, every object is concrete, but there are souls and bodies. Thus, Leibniz’s reism was monistic and spiritualistic, Brentano’s was dualistic, and Kotarbiński’s monistic and materialistic. Although the terminology varies (one can equivalently speak about reism, concretism or nominalism), two claims of any theory going against general (abstract) objects should be very sharply distinguished. The first is formal-ontological and points out the formal feature of existents, namely that they are individuals; but the second is material-ontological or metaphysical and focuses on their nature as physical or psychical entities.