There is the popular notion according to which the world is built up in a hierarchical order, such that combining entities from the lower level results in entities of the next higher level, and so on. It seems beyond doubt in this view that the entities at the lowest level are some subatomic particles, to be followed at the next levels by atoms, molecules, biological organs and organisms including humans, and eventually societies. Accordingly, a scientific discipline is assigned to each (...) level, resulting in a disciplinary hierarchy that starts with physics and goes via chemistry, biology, and psychology to sociology. This popular notion has its merits as it assures us that both the world and our scientific knowledge are perfectly ordered in a harmonious but hierarchical manner. It provides philosophical food to discuss the interfaces between the ontological levels or disciplines in terms of reduction, emergence, supervenience, and so on. And it appeals to some philosophers who are interested in science but unable to read the about two million scientific publications per year, because it allows them to focus on the handful of publications in what is supposed to be the fundamental level of Everything. The hierarchical picture became popular in the 19th century just when most of our scientific disciplines emerged in a process of horizontal diversification, when each discipline carved out and established its own specific subject matter, methodology, theories, and problems and rejected just the idea of the hierarchical dependencies between the disciplines (Stichweh 1984). Despite its anachronism at the time of its popularization, the hierarchical picture was appealing to all those who felt lost in the exploding fields of science and who were yearning for the good old days in which a simple metaphysical scheme could provide order to the entire world. It is more than likely that the hierarchical picture is appealing still nowadays for the same reasons. It would not be worthwhile to discuss the anachronistic hierarchical picture, if it had not such a great appeal to many philosophers.1 In this paper I discuss only one particular problem of the hierarchical picture, the lack of matter or stuffs2 in the ontological hierarchy, which actually consists in a series of structures or forms.. (shrink)