Philosophy
Temporal Parts and the Persistence of Objects Over Time
Quick fact
Philosophers who defend the idea of temporal parts argue that an object is like a 'spacetime worm'—its entire life is a four-dimensional object, and each moment is just one slice.
Why this is interesting
You are not the same person you were as a baby, yet you are still you. How can an object change and still remain the same thing over time?
Read the full explanation
Understanding Temporal Parts and the Persistence of Objects Over Time
Think of a movie reel. The film is a long strip with many individual frames. When you watch it, you experience a continuous story, but the reel itself is a series of still pictures. Perdurantism (or four-dimensionalism) applies this metaphor to objects: an object is a four-dimensional entity that extends through time just as it extends through space. A 'temporal part' is the slice of that object at a particular instant—like a single frame. So, for example, a banana's 'early part' is green and firm, its 'middle part' is yellow, and its 'late part' is brown and mushy. The banana persists because it is the sum of all these parts. This view contrasts with endurantism (three-dimensionalism), which says objects are wholly present at each moment they exist—like a person stepping into different rooms in a house; they are the same person in each room, not a collection of different person-slices. According to endurantism, change is a matter of the same object having different properties at different times. But perdurantism offers a neat solution to puzzles of change: an object can have contradictory properties (like green and yellow) because those properties belong to different temporal parts.
A deeper explanation
The persistence question is about what it means for an object to exist over time. Perdurantism claims that objects persist by having temporal parts. Just as a spatial object (like a road) has different spatial parts (different sections), a temporal object has different temporal parts (different time-slices). This view is motivated by problems such as the Ship of Theseus: if you replace every plank of a ship, is it still the same ship? Perdurantism suggests that the original ship and the replaced ship are different temporal parts of a four-dimensional object—the collection of all planks over time. It handles change by saying that the whole exists at multiple times because its parts exist at those times. This stance is often aligned with the B-theory of time, where past, present, and future are equally real, and time is just another dimension. Endurantism, on the other hand, views persistence as 'being wholly present' at each moment, which requires a deeper explanation for how an object can gain or lose properties while remaining the same. The debate matters not just in metaphysics but also in physics, where special relativity treats time as a dimension on par with space, making the four-dimensional perspective natural. Understanding temporal parts gives you a powerful tool for analyzing questions about identity, change, and the nature of time.