 A few terminological preliminaries. ‘Object’ is used in its narrow sense, which applies only to individual material objects and not to other sorts of entities like numbers or events. ‘Part’ is used in its ordinary sense, on which it is not true—or at least not trivially true—that things are parts of themselves. And when the entry notes that some objects compose something, or that they have a fusion, what is meant is that there is something that has each of them as parts and every part of which overlaps at least one of them. The entry avoids the word ‘sum’, but newcomers to this literature should bear in mind that it gets used in different ways: ‘sum of x and y’ is sometimes used to mean object that is composed of x and y and is other times used to mean object that is composed of x and y and that has all of its parts  essentially.[2]