 The existence pluralist might do better to deny 5, by maintaining that composition is identity. If the world is its proper parts, then positing the former just is positing the  latter.[23]  But there seem to be two main reasons for denying that composition is identity. First, the whole and its parts differ structurally. Pluralities like “the parts” have a privileged structure in terms of their individuals. Thus consider a circle (the whole) divided into two semicircles (the parts). Here the semicircles are structured into a pair of distinct semicircular  shapes.[24]  But (given mereological extensionality) fusions lack such privileged structure. The circle is just as much the fusion of its two semicircles, as it is the fusion of its four quadrants, and its continuum-many points. Second, the whole and its parts differ numerically. As Lewis (1991: 87) writes: “What’s true of the many is not exactly what’s true of the one. After all they are many while it is  one.”[25]  So, assuming that the extended many-one conception of identity retains some analogue of Leibniz’s law of the indiscernibility of identicals, the one whole cannot be identical to its many parts.