On staying the same
According to David Lewis, something 'endures iff it persists by being wholly present at more than one time' (1986: 202). Lewis claims that the 'problem of temporary intrinsics' (PTI, henceforth) is a decisive objection against endurance: 'Persisting things change their intrinsic properties. For instance shape: when I sit, I have a bent shape, when I stand, I have a straightened shape.... How is such change possible?' (1986: 203-204). Robin Le Poidevin explicates the difficulty this way: 'Among the set of past facts is Fa; among the set of present facts is Not-Fa. So reality contains two facts, Fa and Not-Fa, which together form a contradiction' (1998: 38). Lewis's alternative is 'Perdurantism': ordinary material things persist by having parts that exist at different times. Temporary intrinsics belong to different temporal parts. Lewis is bent in the derived sense that he has a part that is bent simpliciter; he sits and stands much as a road is both straight and windy because it has a straight part and a windy part. One way to defend Endurantism against PTI is to deny that shapes are intrinsic properties. Lewis, setting out this view, writes: