Definition
A branch of philosophy that argues that entities are associated temporally while being characterized in an atemporal perspective. It is also called the doctrine of temporal parts
Persistence through time is like extension through space
- Theodore Sider1
Four-dimensionalism borrows a page from the theory of eternalism, which argues that time should be interpreted ontologically. In other words, all parts of time exist (the past, the present, and the future), which is unlike the belief that only the present is real.
Another closely related idea to four-dimensionalism is called perdurantism — the school of thought that considers all temporal parts as real and that the persisting object is the sum of all of its temporal parts. This sum is called a space-time worm
I drew this image to visualize my understanding of a space-time worm. The white object is the entity we’re talking about. The numbers 1 to 6 are different temporal parts. In other words, 6 is where the object is currently at, 5 is where the object was a second ago, and so on. Perdurantism and four-dimensionalism says that all the temporal parts of the ball exist. The ball may have moved but temporally speaking, the ball is still there. It’s as real a thing as the present. Now, if all the temporal parts were summed (or joined, as in the diagram), we get a worm
The Ship of Theseus paradox is explained by four-dimensionalism. The explanation is that the temporal parts of the ship still continue to exist in reality and are all summed to form a space-time worm. The stage view supports the explanation by saying that at every stage, the replacing part is a temporal counterpart of the replaced part
Four-dimensionalism is where instead of saying “X is not a part of Y”, I would say, “X is not a part of Y at time t”. I’m adding time as a descriptor of the object’s existence but not in a temporal sense. This isn’t me saying “X was a part of Y until this time” or “X is a part of Y now” — The concept is not assigning the property of temporal progression to the entity. Rather, it’s about treating time as how space is treated and in an unconditional manner (simpliciter)
Treating time as space
The core of four-dimensionalism is that time is treated not temporally (as in, in terms of time flow) but spatially (as in, the positioning of time as if it were an axis in space)
When we say “I am sitting on a chair”, that is the spatial interpretation of the event as we’re all familiar with. Now, if I were a four-dimensionalist, I would say, “My temporal part is sitting on the chair’s temporal part”. If I stand up, I would say, “One temporal part of mine is sitting in one of the chair’s temporal parts. My other temporal part is not sitting on the chair’s other temporal part”. It is the atemporal view of something that is temporal by nature.
- Four-dimensional feels like temporal palinopsia to me