This thesis takes a closer look at one of the main divisions within contemporary metaphysics. According to constituent ontologies, material objects are fundamentally made of properties, while according to relational ontologies, material objects can only be made of other material objects. Thus, constituent ontologies ascribe a structure to material objects comprising their property parts which is called an ontological structure.
In the first part of the thesis, I examine the consequences of ascribing both ontological structure and ordinary common-sense structure to material objects. Constituent ontologists tell us that ontological structure is basic, while ordinary mereological structure is grounded in or derived from it. However, they rarely lay out the details of how this derivation is supposed to proceed. I examine and criticise various ways this might be done and propose a picture according to which there are two distinct (though related) parthood relations, one relating properties to material objects, and the other relating material objects to material objects.
In the second half of the thesis, I examine the attempts of constituent ontologists to tackle problems related to material coincidence. In particular, I examine the problem of how materially coincident objects could differ qualitatively despite being made of the same matter. Many constituent ontologists have suggested that these problems could be solved by postulating a more fine-grained ontological structure to material objects. I argue that these attempts are not succesful. I also examine if constituent ontologies could help us deal with issues related to persistence.
The tentative conclusion of the thesis is that even if there are coherent versions of constituent ontologies that can succesfully accommodate both ontological and common-sense structure within a single material object, the recent attempts at constituent-style solutions to problems that have previously preoccupied relational ontologists do not give us much reason to prefer constituent ontologies.
