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Four dimensionalism is an ontological view concerned with how objects persist in time. The proponents of four dimensionalism claim that both past and future objects lay equal claims to having the same level of reality as does the present moment. Therefore, if any object x is a past reality, then the past object x is equally as real as the present object. The same line of thinking applies for any future object. If any future object y is a future reality, then the future object y is equally as real as any present object.

Four dimensionalism is commonly expressed by means of a spatial analogue. For an object to have spatial extension, it must have different parts at different locations in space. Temporal parts are subdivided through time in the same way a spatial dimension is subdivided, such as a football field into yards. Just as objects are extended in space, objects are conceptualized as being extended in time.

One who believes in extended mereological simples (from the Greek word μέρος; méros, "part"), maintains that objects do not consist of parts. The view which maintains that objects are wholly present at every moment of their existence is called endurantism. This is in contrast to perdurantism, which maintains that objects are not wholly present at every moment of their existence. Whether or not four dimensionalism applies to both objects and events is a hotly-debated topic among philosophers of time.[1]

The concept of four dimensionalism is in direct contrast to presentism, which asserts that only the present moment exists. The past and future only exist when they are present. Eternalism, which also stands in contrast to presentism, asserts that both things in the past and things yet to exist are eternally real. Both of these concepts are exemplified by the A-series and B-series in the work of J.M.E. McTaggart.


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.[1]

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.[1]

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.[1]

Presentism and Eternalism

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.


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.” [2] 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.[2]

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.[2]

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.[2]

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.[3]

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.”[3]

See also


  1. ^ a b c d Sider, Theodore. "Four Dimensionalism". Philosophical Review. pp. 197–231.  
  2. ^ a b c d "The Unreality of Time". Wikisource. Retrieved 2008-12-15.  
  3. ^ a b "Time". Stanford Encyclopedia of Philosophy. 2002-11-25. Retrieved 2008-12-15.  

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


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