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In philosophy, four-dimensionalism (also known as the the doctrine of temporal parts and the theory that objects "perdure") is the philosophical theory that persistance through time is like 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. Contemporary four-dimensionalists include, according to Sider (1997), Armstrong (1980), Hughes (1986) , Heller (1884, 1990,1992,1992) and Lewis (1983, 1986).

Four-dimensionalism may refer to either eternalism or perdurantism. 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. 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 would be incoherent.

Background

As four-dimensionalism (understood as either eternalism or perdurantism) is a metaphysical theory, it is necessary to say something here about the aim of metaphysics. Like science, the aim of metaphysics is to understand as much as possible in terms of as little as possible. In other words, the aim is to reduce the number of fundamentals to a minimum, and understand everything else as if constructed in some simple way out of those fundamentals. If a theory of x maintains that x is a fundamental element of reality, then this is expressed in this article by saying that the theory is a metaphysical "dead end" theory (of x). The background assumption is that reduction of fundamentals will lead to a true picture of reality. If we can understand space in terms of fundamentals x, y, z, etc., then all the better if we can also understand time in terms of x, y, z, etc. Eternalism attempts to do just that. Time is understood as the fourth dimension, equivalent to the three dimensions of space. What we lose from this theory is any special status for the present, however special it might seem...

Temporal parts

The idea of a whole object being composed of smaller parts is not revolutionary. On the contrary, this notion is rather common. One instance of a whole object losing a part is the paradigm example of the Ship of Theseus. Another illustration is a familiar routine such as getting a haircut. Both of these instances provide an example of a whole object losing a part. For the four-dimensionalist, this does not represent the notion of parthood.

The notion of parthood for a four-dimensionalist allows one to speak of the parts of an object simpliciter. That is, without any criterion or condition, versus at any particular time such as t₁ or t₂. Within the framework of four-dimensionalism, one could say that his or her current temporal part is sitting at a computer, typing up a presentation on four-dimensionalism, wearing sweatpants and having tea. Therefore, a four-dimensionalist conceives of the parts of an object as an atemporal relation, or part of a larger spacetime worm. A spacetime worm is a four-dimensional object consisting of a three-dimensional object extending through the fourth dimension of time.

Furthermore, the notion of parthood allows a four-dimensionalist to account for change, in a basic and ordinary sense of the word. Change is what allows one to distinguish between different successive temporal parts. For example, one temporal part of a person may be typing at a computer, while another temporal part will be going to sleep. Still a third temporal part will be waking up to run errands and get prepared for work later in the evening.

Presentism vs. eternalism

Consider the proposition: there was an American president called Reagan. What are the truth conditions? According to presentism, we cannot say! According to eternalism, we can say the following: there is an American president called Reagan, in the past. We can only say that, if the past exists. How can Reagan exist in the past if the past doesn't exist? We can understand "was" in terms of "is" and "past", but only if the past exists. The past is understood as a time before the present. If you can understand the idea of someone existing in the present, and you understand the idea of a linearly ordered sequence (i.e., time), then you can understand the idea of someone existing in the past! It is just a simple set theoretic model of time. "Was" just means "is" at some point before the present (i.e., at some point before, or "less than", one's current coordinate on the time line). What is unclear, however, is that just because we can understand (model) time in this eternalist manner, does that mean that reality is really like that? Does the past really exist, and what does that mean, anyway? Or, is the model just a formal device which is useful to adopt for some theoretical purposes? Applying the model to the future does, however, seem to raise issues relating to determinism and free will.

A-series and B-series

J.M.E. McTaggart famously argues in his 1908 paper The Unreality of Time that time is necessarily unreal. McTaggart introduces three different types of ordered relations among events: the A-series, the B-series and the C-series. The A-series is “the series of positions running from the far past through the near past to the present, and then from the present to the near future and the far future.” The basic temporal distinctions of past, present and future are fundamental and unique to the A-series as well as essential to the reality of time. If the distinctions of past, present and future are not true of reality, then there is no reality in time. The A-series is championed by proponents of presentism.

The B-series is a series of positions that is ordered from earlier to later. Like the A-series, the B-series contains a direction of change. Unlike the A-series, the B-series does not define a present moment that separates past and future. Events are thought to exist earlier and later, rather than in the past or future. This distinction allows one to move away from the terminology employed in the basic conception of time.

The A-series maintains that time is running from past to future while the B-series asserts that events are running from earlier to later, therefore both require a direction. The C-series, consequently, postulates that events have an order but that there is no inherent direction of time. McTaggart asserts that the order of the events does not necessitate change, a concept that he has already established to be necessary to the concept of time. Therefore, the C-series is atemporal and offers a plausible alternative to the conventional conception of time as well as a part of the concept of eternalism.

Comparisons to three-dimensionalism

The three dimensionalist view imagines time as being a unique dimension, 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 believes that objects can be differentiated based on their spatial dimensions, the same does not apply to time. Rather, the existence of temporal parts is a linguistic construct. For example, the person described by the phrase “Descartes in 1635” is objectively the same as the person described as “Descartes in 1620.” Temporal parts are not existent for the three dimensionalist. Therefore, change does not need to be accounted for. Accordingly, the only relation between these objects is that of identity. This helps to account for the paradox of change.

The four-dimensionalist view, by contrast, asserts that all objects occupying different time frames are inherently different versions of the same object. In order to account for these different versions, the notion of temporal parts is introduced. Differences among temporal parts are how a four-dimensionalist accounts for change. Thus, the temporal part described by the phrase “Descartes in 1635” is different from the temporal part described by the phrase “Descartes in 1620.” When combined, these parts form a spacetime “worm.”

See also

• Rietdijk–Putnam argument for an argument advocating this position.

References

1. ^ Sider, Theodore (1997). "Four-Dimensionalism" (PDF). The Philosophical Review. 106 (2). Duke University Press: 197–231. JSTOR 2998357. {{cite journal}}: Unknown parameter |month= ignored (help)
2. Kuipers, Theo A.F. (2007). General Philosophy of Science: Focal Issues. North Holland. p. 326. ISBN 978-0444515483.
3. Hawley, Katherine (2010). "Temporal Parts". In Edward N. Zalta (ed.). The Stanford Encyclopedia of Philosophy (Winter 2010 ed.).
4. ^ "The Unreality of Time". Wikisource. Retrieved 2008-12-15.
5. ^ "Time". Stanford Encyclopedia of Philosophy. 2002-11-25. Retrieved 2008-12-15.

• 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/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: 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

External links

• 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

• Philosophy of time
• Philosophy of physics
• Spacetime