In philosophy, four-dimensionalism (also known as the doctrine of temporal parts and the theory that objects "perdure") is an ontological position that an object's persistence through time is like its extension through space and an object that exists in time has temporal parts in the various subregions of the total region of time it occupies.
Eternalism is a philosophical approach to the ontological nature of time, according to which all points in time are equally "real", as opposed to the presentist idea that only the present is real. Perdurantism—or perdurance theory—is a philosophical theory of persistence and identity, according to which an individual has distinct temporal parts throughout its existence. Thus eternalism is a theory of time, while perdurantism is a theory about the identity of objects over time. Sider (1997) uses the term four-dimensionalism to refer to perdurantism. Michael Rea (Forthcoming in The Oxford Handbook for Metaphysics), however, uses the term "four-dimensionalism" to mean the view that presentism is false as opposed to "perdurantism", the view that objects last over time without being wholly present at every time at which they exist.
Eternalism and perdurantism tend to be discussed together because many philosophers argue for a combination of eternalism and perdurantism, considering both as better theories than their counterparts, presentism and endurantism, respectively. It may be argued that the acceptance of perdurantism and rejection of eternalism would be incoherent.
Contemporary four-dimensionalists include, according to Sider (1997), Armstrong (1980), Hughes (1986), Heller (1984, 1990,1992,1993) and Lewis (1983, 1986).
Temporal parts is a concept used in contemporary metaphysics in the debate over the persistence of material objects. Objects typically have parts that exist in space—a human body, for example, has spatial parts like hands, feet, and legs.
Presentism vs. eternalism (and the growing block theory)
Presentism is an ontological viewpoint which attempts to account for how consciousness functions in relation to time. Presentism asserts that only the present exists. The past and the future, therefore, are seen as non-existent. To a presentist, the memory accounts for the collection of events that have already occurred. Similarly, the future is conceptualized as being a mental construct. Therefore, presentism is attempting to demonstrate that the total sum of the actual world occupies the present moment.
Consequently, eternalism is the ontological view which postulates that past, present and future all equally exist. While the presentist asserts that the past and future are only logical constructs, the eternalist believes that time exists as an objective manifestation. Eternalism is the basic construct behind four-dimensionalism, as it accounts for the reality of past and future rather than proposing that all events occupy the present.
Additionally there is the "growing block theory" which accepts present and past objects (and events) into its ontology but not future ones. This purportedly allows for an open future (and closed past), thus making room for libertarian free will. It also makes good on the intuition that there is a significant metaphysical distinction to be made between past and future.
A-series and B-series
J.M.E. McTaggart in The Unreality of Time, identified two descriptions of time, which he called the A-series and the B-series. The A-series identifies positions in time as past, present, or future, and thus assumes that the "present" has some objective reality, as in both presentism and the growing block universe. The B-series defines a given event as earlier or later than another event, but does not assume an objective present, as in four-dimensionalism.
Comparisons to three-dimensionalism
Unlike the four dimensionalist, the three dimensionalist considers time to be a unique dimension that is not analogous to the three spatial dimensions: length, width and height. Whereas the four dimensionalist proposes that objects are extended across time, the three dimensionalist adheres to the belief that all objects are wholly present at any moment at which they exist. While the three dimensionalist agrees that the parts of an object can be differentiated based on their spatial dimensions, they do not believe an object can be differentiated into temporal parts across time. For example, in the three dimensionalist account, "Descartes in 1635" is the same object as "Descartes in 1620", and both are identical to Descartes, himself. However, the four dimensionalist considers these to be distinct temporal parts, neither of which are identical with the whole Descartes, the spacetime "worm" concatenating these temporal parts.
- Rietdijk–Putnam argument for an argument advocating this position.
- Sider, Theodore (April 1997). "Four-Dimensionalism" (PDF). The Philosophical Review (Duke University Press) 106 (2): 197–231. JSTOR 2998357.
- Kuipers, Theo A.F. (2007). General Philosophy of Science: Focal Issues. North Holland. p. 326. ISBN 978-0-444-51548-3.
- Hawley, Katherine (2010). "Temporal Parts". In Edward N. Zalta. The Stanford Encyclopedia of Philosophy (Winter 2010 ed.).
.. This view is variously called "four-dimensionalism", "perdurantism", or "the doctrine of temporal parts". Some think that four-dimensionalism understood as the denial of presentism implies four-dimensionalism understood as perdurantism. But whether or not that is true, the important thing to recognize is that these are two very different views. 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.
— MICHAEL C. REA, FOUR DIMENSIONALISM, Forthcoming in The Oxford Handbook for Metaphysics)
- Presentism and the Space-Time Manifold by Dean Zimmerman, p. 7
- "Time: The 3D/4D Controversy". Stanford Encyclopedia of Philosophy. 2002-11-25. Retrieved 2008-12-15.
As in the case of the disputes between A Theorists and B Theorists, on the one hand, and Presentists and Non-presentists, on the other hand, the 3D/4D controversy is part of a general disagreement among philosophers of time concerning the degree to which time is dissimilar from the dimensions of space. That general disagreement has been an important theme in the philosophy of time during the last one hundred years, and will most likely continue to be so for some time to come.
- Armstrong, David M. (1980). "Identity Through Time". In Peter van Inwagen (ed.), Time and Cause, 67-68 Dordrecht: D. Reidel.
- Hughes, C. (1986). "Is a Thing Just the Sum of Its Parts?" Proceedings of the Aristotelian Society 85: 213-33.
- Heller, Mark (1984). "Temporal Parts of Four Dimensional Objects". Philo-
sophical Studies 46: 323-34. Reprinted in Rea 1997: 12.-330.
- Heller, Mark (1990). The Ontology of Physical Objects: Four-dimensional Hunks of Matter.
Cambridge: Cambridge University Press.
- Heller, Mark (1992). "Things Change". Philosophy and Phenomenological Research 52: 695-304
- Heller, Mark (1993). "Varieties of Four Dimensionalism". Australasian Journal of Philosophy 71: 47-59.
- Lewis, David (1983). "Survival and Identity". In Philosophical Papers, Volume 1, 55-7. Oxford: Oxford University Press. With postscripts. Originally published in Amelie O. Rorty, ed., The Identities of Persons (Berkeley: University of California Press, 1976), 17-40.
- Lewis, David (1986a). On the Plurality of Worlds. Oxford: Basil Blackwell.
- Lewis, David (1986b). Philosophical Papers, Volume 2. Oxford: Oxford University Press.
- McTaggart John Ellis (1908). "The Unreality of time" in Mind: A Quarterly Review of Psychology and Philosophy 17 (1908): 456-473. <http://en.wikisource.org/wiki/The_Unreality_of_Time>
- Lewis, D. 1976: Survival and identity. Pp. 17-40 in Rorty, A.O. (ed.) The identities of persons. Berkeley: University of California Press. Google books
- Markosian, N. 2004: A defense of presentism. Pp. 47-82 in Zimmerman, D.W. (ed.) Oxford Studies in Metaphysics, Volume 1. Oxford: Oxford University Press. Google books
- Muis, R. 2005: [Review of] Four-dimensionalism: an ontology of persistence and time. By Theodore Sider. Ars Disputandi, 5 ISSN: 1566-5399 PDF
- Robinson, D. 1985: Can amoebae divide without multiplying? Australasian journal of philosophy, 63(3): 299–319. doi:10.1080/00048408512341901
- Rea, M. C., "Four Dimensionalism" in The Oxford Handbook for Metaphysics. Oxford Univ. Press. Describes presentism and four-dimensionalism.
- "Time" in the Internet Encyclopedia of Philosophy
T Sider - 2003 - arsdisputandi.org, Four-dimensionalism: An ontology of persistence and time, Cited by 744 http://www.arsdisputandi.org/publish/articles/000200/article.pdf. In analytical metaphysics, there are three, closely related, debates about time and the nature of change and persistence. The first is about what there is. Presentists believe that only present things exist, whereas eternalists think that also past and future things exist, even though ...
- MICHAEL C. REA- The Oxford handbook of metaphysics, 2003 - books.google.com, Four-dimensionalism,
CHAPTER 9 FOUR-DIMENSIONALISM i. INTRODUCTION. Cited by 48 . FOUR-DIMENSIONALISM, as it will be understood in this chapter, is a view about the ontological status of non-present objects. Presentists say that only present objects exist. There are no ...
- K Koslicki - Philosophical Studies, 2003 - Springer, The crooked path from vagueness to four-dimensionalism. Cited by 37 
How do the familiar concrete objects of common-sense – houses, trees, people, cars and the like – persist through time? According to the position known as 'four-dimensionalism' or 'the doctrine of temporal parts', ordinary concrete objects persist through time by perduring, i.e., by ...
- Markosian - Philosophy and Phenomenological Research, 2004 - Wiley Online Library
2, Two Arguments from Sider's Four‐Dimensionalism, Cited by 19 . The Argument from Vagueness Sider's argument from vagueness for Four-Dimensionalism is adapted from his reconstruction of David Lewis's argument for the following conclusion about fusions.2 ... The Principle of Universal Fusions (PUF): Every class of objects has a fusion.
- Miller - Erkenntnis, 2005 - Springer, The metaphysical equivalence of three and four dimensionalism. Cited by 15 . ABSTRACT. I argue that two competing accounts of persistence, three and four dimensionalism, are in fact metaphysically equivalent. I begin by clearly defining three and four dimensionalism, and then I show that the two theories are inter- translatable and equally ...