The two topics “the categories of being” and “the ontological structure of objects” are intimately related to each other and to the problem of universals. It is not possible to propose a solution to the problem of universals that does not have implications for the topic “the categories of being”. (Even nominalism implies that at least one popular candidate for the office “ontological category” is non-existent or empty.) It is certainly possible to maintain that there are ontological categories that are not directly related to the problem of universals (“proposition”, “state of affairs”, “event”, “mere possibile”), but any philosopher who maintains this will nevertheless maintain that if there are universals they make up at least one of the higher ontological sub-categories. And it seems that it is possible to speak of ontological structure only if one supposes that there are objects of different ontological categories. So whatever metaphysics comprehends, it must comprehend every aspect of the problem of universals and every aspect of the topics “the categories of being” and “the ontological structure of objects”. For a recent investigation of the problems that have been discussed in this section, see Lowe (2006).