ABSTRACT
There are various different mereological systems, which differ over exactly what the features of parthood are. For instance, there is a division over the logical properties of the parthood relation: the vast majority of metaphysicians think it is transitive – others demur. There is a division over whether everything has proper parts (and therefore everything is made of gunk) or whether some things have no proper parts (and are so simple). There is a division concerning the circumstances under which objects come to compose a further object; for instance, whether or not some atoms arranged in the formation of a table compose a table (which we would naturally think is the case) and whether or not several atoms scattered haphazardly across the galaxy compose a bizarre, scattered object (which we would naturally think is not the case; see Special Composition Question for more). And there is a dispute over whether or not if two objects have exactly the same parts they are identical.
