A main function of common natures in Avicenna’s metaphysics is supposed to be providing an objective ground for the categories. Thus, it is commonly assumed that in his metaphysics things are objectively divided into the categories into which they are because members of each category share the same common nature. However, common natures cannot perform the function unless they are shared, in a real sense of the word, by the members of the respective categories, and it is not clear at (...) all in what real sense Avicenna took common natures to be shared by them. On the one hand, he rejected Platonic and Aristotelian realisms about common natures, the two standard accounts of how common natures are shared by their instances. On the other hand, it is unclear that his alternative account(s) of common natures renders them genuinely common. The primary goal of this paper is to examine whether Avicenna’s common natures can provide an objective ground for the categories. It considers various interpretations of Avicenna's account and argues that they are either incorrect interpretations of Avicenna or do not render common natures genuinely common. It concludes with proposing to look elsewhere in Avicenna’s system to find the objective ground. (shrink)