Wikipedia
In philosophy, four-dimensionalism (also known as the doctrine of temporal parts and the theory that objects "perdure") is an ontological position that an object's persistence through time is like its extension through space and an object that exists in time has temporal parts in the various subregions of the total region of time it occupies.
Eternalism is a philosophical approach to the ontological nature of time, according to which all points in time are equally "real", as opposed to the presentist idea that only the present is real.
Perdurantism—or perdurance theory—is a philosophical theory of persistence and identity, according to which an individual has distinct temporal parts throughout its existence. Thus eternalism is a theory of time, while perdurantism is a theory about the identity of objects over time. Sider (1997) uses the term four-dimensionalism to refer to perdurantism. Michael Rea (Forthcoming in The Oxford Handbook for Metaphysics), however, uses the term "four-dimensionalism" to mean the view that presentism is false as opposed to "perdurantism", the view that objects last over time without being wholly present at every time at which they exist.
Eternalism and perdurantism tend to be discussed together because many philosophers argue for a combination of eternalism and perdurantism, considering both as better theories than their counterparts, presentism and endurantism, respectively. It may be argued that the acceptance of perdurantism and rejection of eternalism would be incoherent.
Contemporary four-dimensionalists include, according to Sider (1997), Armstrong (1980), Hughes (1986), Heller (1984, 1990,1992,1993) and Lewis (1983, 1986).