 As we have seen in invoking temporal parts or stages Lewis endorses one species of what has come to be called Four Dimensionalism. The expression ‘Four Dimensionalism’ has been applied to a number of different positions that it is well to distinguish here since not all of them are relevant to identity across time. ‘Four Dimensionalism’ has sometimes been used for the thesis, particularly associated with Relativity Theory, that time is space like. On another use of ‘Four Dimensionalism’ a persisting thing is identical with its history. On this view an object is a sequence of events. Sometimes ‘Four Dimensionalism’ is used to label the view that, contra Presentism, things past present and future are equally real.