Four Dimensionalism Argument

Overview and Background

The Four Dimensionalism Argument is a family of arguments in contemporary metaphysics that supports four-dimensionalism (often called perdurantism): the thesis that ordinary objects are extended in time as well as in space and are composed of temporal parts. On this view, a persisting object is a four‑dimensional “worldtube” in spacetime, whose different temporal segments possess different properties.

The argument is developed in response to questions about persistence, change, and the ontology of time, and is usually contrasted with three‑dimensionalism or endurantism, according to which ordinary objects are wholly present at each moment of their existence and do not have temporal parts. Although antecedents appear in the work of J. M. E. McTaggart and others, the argument was prominently and systematically defended by David Lewis and Ted Sider, especially in Sider’s book Four-Dimensionalism (2001).

Rather than a single canonical proof, “the Four Dimensionalism Argument” refers to a cluster of interrelated lines of reasoning, many of which appeal to problems about change, persistence, vagueness, and compatibility with modern physics.

Core Formulations of the Argument

A central version of the argument focuses on persistence through change:

1. Reality of change: Objects such as people, trees, and planets genuinely change over time. A person may be short at one time and tall at a later time, or a statue may be intact and later damaged.

2. Problem for endurantism: Under endurantism, the very same wholly present object is first short and later tall, or first intact and later damaged. If it is literally the same entire object, then it seems that one and the same thing has incompatible properties (short and not-short, intact and not-intact). Endurantists appeal to tensed or time-indexed properties (“is short at t1”, “is tall at t2”) to avoid outright contradiction.

3. Temporal parts solution: Four-dimensionalism explains change by holding that different temporal parts (or “stages”) of an object bear different, non-contradictory properties: the earlier temporal part is short, the later temporal part is tall. The persisting person is the whole four-dimensional series of these parts.

4. Avoiding contradiction: On this account, there is no single three-dimensional entity that is both short and tall; rather, different temporal segments bear different properties, much as different spatial parts of a road can be straight here and curved there without contradiction.

5. Explanatory preference: Proponents claim that this picture provides a more uniform and metaphysically elegant explanation of change than endurantism, which must explain how an object can be wholly present at different times yet have temporally varying properties.

Further versions of the argument draw on other phenomena:

• Argument from vagueness: Sider and others argue that if it is vague when an object begins or ceases to exist, then—assuming there are no vague matters of existence—there must be many closely related but distinct objects extended across time. This is taken to fit naturally with four-dimensionalism, which already allows for many overlapping temporal “worms” or stages in spacetime.

• Argument from temporary intrinsics: Following Lewis, some versions emphasize temporary intrinsic properties (like shape or mass) that seem to characterize an object “in itself” at a time. The temporal-parts theory allegedly gives a cleaner account: each temporal part has its own intrinsic properties, rather than requiring that all such properties be relativized to times.

Motivations and Theoretical Advantages

Supporters hold that the Four Dimensionalism Argument gains additional force from its theoretical virtues and its relation to modern physics:

• Analogy between time and space: If time is a dimension analogous to spatial dimensions, it is natural to think that objects are extended in time as they are in space. Just as an object has distinct spatial parts, it might have distinct temporal parts.

• Compatibility with relativity: Special and general relativity treat spacetime as a unified four‑dimensional manifold without an absolute, global present. Proponents argue that a four‑dimensional ontology meshes more smoothly with this framework than a picture that privileges a moving three‑dimensional present.

• Unified treatment of persistence and identity: Four-dimensionalism offers a single model—extension in spacetime—for understanding how objects persist, how they survive change, and how they relate to counterpart objects across time and possible worlds.

• Handling of puzzles about fission and fusion: Cases where an object splits (fission) or merges (fusion), or puzzles about ships gradually replaced plank by plank, can be modeled as patterns of overlapping temporal parts, making identity through time less mysterious.

Because of these features, the Four Dimensionalism Argument is often framed as an inference to the best explanation: given the data about change, persistence, and physical theory, four-dimensionalism is said to offer the most coherent overall picture.

Criticisms and Ongoing Debates

The argument remains controversial, and defenses of three-dimensionalism challenge it on multiple fronts:

• Tensed properties and truthmaking: Endurantists argue that the appeal to tensed or time-indexed properties is not ad hoc but reflects the way ordinary language and temporal logic already operate. They contend that there is no genuine contradiction in saying “the same person is short at t1 and tall at t2,” since the temporal modifiers block inconsistency.

• Intuitiveness and common sense: Critics maintain that four-dimensionalism significantly departs from common sense. We ordinarily conceive of ourselves as wholly present now, not as extended spacetime worms with only a temporal slice present at any moment.

• Ontological cost: Some argue that four-dimensionalism multiplies entities by introducing an extensive ontology of temporal parts, raising questions about parsimony. Endurantists claim they can explain the same phenomena without positing an additional category of parts.

• Interpretation of physics: Although relativity is often invoked in support of four-dimensionalism, opponents argue that physical theory does not straightforwardly decide metaphysical questions about persistence. They claim that endurantism can be reformulated in relativistic-friendly terms.

• Alternative accounts of persistence: Varieties of stage theory, presentism, and neo-endurantism offer different ways of accommodating the data about change and time. These rival views challenge the Four Dimensionalism Argument’s claim to be the uniquely best explanation.

In contemporary metaphysics, the Four Dimensionalism Argument thus functions as a central point of dispute about how to understand time, change, and the existence of ordinary objects, with no consensus yet reached on its ultimate soundness.