‘Are wholes just sums of parts?’ considers the relation between wholes and their parts. In metaphysics an object is said to be complex, meaning it has parts. But how does a mobile phone differ from a pile of stones? They are both made up of individual parts, but philosophers sometimes distinguish substances: the integrated wholes from mere aggregates. The phone had an ability to receive calls, which its parts did not. Can the ability of the whole be explained entirely in terms of the parts? The reductionist view insists that the parts can ultimately explain all the workings of the whole. Emergentism, however, claims that wholes are more than sums of parts.