The principal thesis of Kotarbiński's ontology states that things and only things exist. This is the thesis of reism (concretism). Reism has also its semantic dimension because it contains a view of language. These two aspects, ontological and semantic, were at first parallel to one another, but later reism became primarily a semantic view. As he moved toward a semantic formulation, Kotarbiński enriched reism with additional theses on things. Reism was an original construction of Kotarbiński, although already after having formulated his views he noted (1966a) that he had forerunners in Leibniz and Brentano. Thus, reism may be said to have emerged from the general theory of objects of Brentano and Twardowski.¹