 Second, it often seems that whether or not an object survives a certain kind of change is in some sense conventional, or up to us. Many believe that we set the standards for how many repairs you can make to your bicycle without destroying it, and that whether or not a person can survive massive memory loss is partly a matter of what we mean by ‘person’. How things persist seems sometimes to be a matter of what kind of classifications we choose to use. A radical version of this suggests that physical objects come into and out of existence when we decide they do. This sounds mysterious: how could we have such powers? But the combination of universalism and perdurantism permits a less radical version of the view: there are lots of four-dimensional objects which share temporal parts with the wheeled thing in your bike shed, and it’s up to us which one of those counts as a ‘bicycle’. Similarly, perhaps it’s up to us which of the multitude of four-dimensional objects count as ‘people’. 