Why cannot each special science, be it empirical or a priori, address its own ontological questions on its own behalf, without recourse to any overarching ‘science of being’? The short answer to this question is that reality is one and truth indivisible. Each special science aims at truth, seeking to portray accurately some part of reality. But the various portrayals of different parts of reality must, if they are all to be true, fit together to make a portrait which can be true of reality as a whole. No special science can arrogate to itself the task of rendering mutually consistent the various partial portraits: that task can alone belong to an overarching science of being, that is, to ontology. But we should not be misled by this talk of ‘portraits’ of reality. The proper concern of ontology is not the portraits we construct of it, but reality itself.