In philosophy, four-dimensionalism (also known as the doctrine of temporal parts) is the ontological position that an object's persistence through time is like its extension through space.
Thus, an object that exists in time has temporal parts in the various subregions of the total region of time it occupies, just like an object that exists in a region of space has at least one part in every subregion of that space.
[1] Four-dimensionalists typically argue for treating time as analogous to space, usually leading them to endorse the doctrine of eternalism.
Sider (1997)[1] uses the term four-dimensionalism to refer to perdurantism, but Michael Rea uses the term "four-dimensionalism" to mean the view that presentism is false as opposed to "perdurantism", the view that endurantism is false and persisting objects have temporal parts.
Much of the contemporary literature in the metaphysics of time has been taken to spring forth from this distinction, and thus takes McTaggart's work as its starting point.
A contemporary account of this paradox is introduced in Ney (2014),[3] but the original problem has its roots in Greek antiquity.
Secondly, problems of temporary intrinsics are argued to be best explained by four-dimensional views of time that involve temporal parts.
Lewis argues that separate temporal parts having the incompatible properties best explains an object being able to change its shape in this way, because other accounts of three-dimensional time eliminate intrinsic properties by indexing them to times and making them relational instead of intrinsic.
To avoid confusion, I will in this paper reserve the term "four-dimensionalism" exclusively for the view that presentism is false, and I will use the term "perdurantism" to refer to the view that objects last over time without being wholly present at every time at which they exist.