The Nature of Time
Does time really flow, with an objective present that moves from past toward future, or is temporal passage an illusion projected onto a static array of events? This topic examines the deepest questions about the nature of time.
Definition
The metaphysics of time concerns whether temporal passage and tense are objective features of reality, and how the structure of time is to be characterized.
Scope
Covers McTaggart's A-series and B-series, the A-theory and B-theory of time, the reality of tense, the direction and asymmetry of time, and the bearing of physics on the metaphysics of temporal passage.
Core questions
- Is there an objective, moving present?
- Are tensed facts irreducible, or reducible to tenseless relations?
- What grounds the direction or arrow of time?
- Does relativistic physics support the B-theory?
Key concepts
- A-series
- B-series
- Tense
- Temporal passage
- Arrow of time
- Tenseless facts
Key theories
- A-theory and tense realism
- The A-theory holds that the present is metaphysically privileged and that tensed facts about what is past, present, or future are irreducible; Prior developed tense logic to formalize this view.
- B-theory and tenseless time
- The B-theory holds that reality consists of events tenselessly ordered by earlier-than and later-than relations; apparent passage is explained away, as in Mellor's account, without an objective moving present.
History
McTaggart's 1908 paper introduced the A-series and B-series and argued that time is unreal. Russell and later Mellor developed tenseless B-theories, while Prior built tense logic to vindicate the A-theory. The debate now engages closely with the physics of spacetime.
Debates
- Is temporal passage real?
- A-theorists treat passage and the present as objective; B-theorists argue passage is a feature of experience rather than time itself and often appeal to the relativity of simultaneity against a privileged present.
Key figures
- J. M. E. McTaggart
- Arthur Prior
- D. H. Mellor
- Hugh Mellor
- Bertrand Russell
Related topics
Seminal works
- mctaggart1908
- prior1967
Frequently asked questions
- What did McTaggart mean by the A-series and B-series?
- The A-series orders events as past, present, and future, capturing temporal passage. The B-series orders them by the fixed relations earlier-than and later-than. McTaggart argued the A-series is contradictory yet essential to time, concluding that time is unreal.