Temporal parts

In contemporary metaphysics, temporal parts are the parts of an object that exist in time. A temporal part would be something like "the first year of a person's life", or "all of a table from between 10:00 a.m. on June 21, 1994 to 11:00 p.m. on July 23, 1996". The term is used 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. Some metaphysicists believe objects have temporal parts as well.

Originally it was argued that those who believe in temporal parts believe in perdurantism, that persisting objects are wholes composed entirely of temporal parts. This view was contrasted with endurantism, the claim that objects are wholly present at any one time (thus not having different temporal parts at different times). This claim is still commonplace, but philosophers like Ted Sider believe that even endurantists should accept temporal parts.


Not everyone was happy with the definition by analogy: some philosophers, such as Peter van Inwagen, argued that—even given the definition by analogy—they still had no real idea what a temporal part was meant to be (1981: 133), whilst others have felt that whether temporal parts existed or not is merely a verbal dispute (Eli Hirsch holds this view).

Gallois surveys some of the attempts to create a more specific definition (Gallois 1998: 256). The early attempts included identifying temporal parts with ordered pairs of times and objects, but it seems relatively unproblematic that temporal parts exist given the definition and ordered pairs seem unsuitable to play the role that perdurantists demand, such as being parts of persisting wholes—how can a set be a part of a material object? Later perdurantists identified persisting objects with events, and as events having temporal parts was not problematic (for example, the first and second halves of a football match), it was imagined that persisting objects could have temporal parts. There was a reluctance from many to identify objects with events, and this definition has long since fallen out of fashion.

Of the definitions closest to those commonly used in the literature, the earliest was Thomson:

x is a cross-sectional temporal part of y =df (∃T)[y and x exist through T & no part of x exists outside T & (∀t)(t is in T ⊃ (∀P)(y exactly occupies P at tx exactly occupies P at t))] (Thomson 1983: 207).

Later, Sider tried to combat the fears of endurantists who could not understand what a temporal part is by defining it in terms of "part at a time" or "parthood at a time", a relation that the endurantist should accept, unlike parthood simpliciter—which an endurantist may say makes no sense, given that all parts are had at a time. (However, McDaniel argues that even endurantists should accept that notion [McDaniel (2004) 146-7]). Sider gave the following definition, which is widely used:

x is an instantaneous temporal part of y at instant t =df (i) x is a part of y; (ii) x exists at, but only, at t; and (iii) x overlaps every part of y that exists at t. (Sider 2001: 60).

Sider also gave an alternative definition that is compatible with presentism, using the tensed operators "WILL" and "WAS":

x is an instantaneous temporal part of y =df (i) x is a part of y; (ii) x overlaps every part of y; (iii) it is not the case that WILL (x exists); (iv) it is not the case that WAS (x exists). (Sider 2001: 71).

While Sider's definition is most commonly used, Zimmerman—troubled by the demand for instants (which may not exist in a gunky space-time that is such that every region has a sub-region)—gives the following:

x is a temporal part of y throughout T =df (i) x exists during and only during T; (ii) for every subinterval T* of T, there is a z such that (a) z is a part of x, and (b) for all u, u has a part in common with z during T* if and only if u has a part in common with y during T*; and (iii) y exists at times outside of T. (Zimmerman 1996: 122)

The argument from temporary intrinsics

Temporal parts are sometimes used to account for change. The problem of change is just that if an object x and an object y have different properties, then by Leibniz's Law, one ought to conclude that they are different. For example, if a person changes from having long hair to short hair, then the temporal-parts theorist can say that change is the difference between the temporal parts of a temporally extended object (the person). So, the person changes by having a temporal part with long hair, and a temporal part with short hair; the temporal parts are different, which is consistent with Leibniz's Law.

However, those who reject the notion that ordinary objects, like people, have temporal parts usually adopt a more common-sense view. They say that an object has properties at times. In this view, the person changes by having long hair at t, to short hair at t'. To them, there is no contradiction in thinking an object is capable of having different properties at different times.

An argument widely held to favor the concept of temporal parts arises from these points (Sider, 2001): David Lewis' argument from temporary intrinsics, which he first advanced in On the Plurality of Worlds.[1] The outline of the argument is as follows:

P1: There are intrinsic properties, i.e., properties had by an object independently of anything in the world.
P2: If every property had by an object is had to times, then there are no intrinsic properties.
C1: Therefore, not every property had by an object is had two times. Objects have some of their properties intrinsically, i.e., simpliciter.
P3: But only temporal parts can have their properties simpliciter.
C2: Therefore, there are temporal parts. (For this to follow, it is required that there be objects).

Premise P1 is an intuitive premise; generally we distinguish between properties and relations. An intrinsic property is just a property that something has independently of anything else; an extrinsic property is had only in relation to something. An example of an extrinsic property is "fatherhood": something is a father only if that something is a male and has a child. An example of an alleged intrinsic property is "shape".

According to Lewis (Sider, 2001), if we know what "shapes" are, we know them to be properties, not relations. However, if properties are had to times, as endurantists say, then no property is intrinsic. Even if a ball is round throughout its existence, the endurantist must say "for all times in which the ball exists, the ball is round, i.e., it is round at those times; it has the property 'being round at a time'." So, if all properties are had to times, then there are no intrinsic properties, (premise P2).

However, if we think that Lewis is right and some properties are intrinsic, then some properties are not had to times—they are had simpliciter (premise C1).

It might be said that premise P3 is more controversial. For instance, suppose a timeless world is possible. If that were so, then in that world, even if there were intrinsic properties, they would not be had by temporal parts—since by definition a timeless world has no temporal dimension, and therefore in such a world there cannot be temporal parts. However, our world is not timeless, and the possibility of timeless worlds is questionable, so it seems reasonable to think that in worlds with a temporal dimension, only temporal parts can have properties simpliciter.

This is so because temporal parts exist only at an instant, and therefore it makes no sense to speak of them as having properties at a time. Temporal parts have properties, and have a temporal location. So if person A changes from having long hair to having short hair, then that can be paraphrased by saying that there is a temporal part of A that has long hair simpliciter and another that has short hair simpliciter, and the latter is after the former in the temporal sequence; that supports premise P3.

Premise C2 follows, so long as one is not considering empty worlds—if such worlds are even possible. An empty world doesn't have objects that change by having a temporal part with a certain property and another temporal part with a certain other property.

Premise P1, the key premise of the argument, can be coherently denied even if the resulting view—the abandonment of intrinsic properties—is counterintuitive. There are, however, ways to support the argument if one accepts relationalism about space-time.

See also


  1. ^ 1941-2001., Lewis, David K. (David Kellogg), (1986-01-01). On the plurality of worlds. B. Blackwell. OCLC 12236763.
  • Gallois, A. 1998. Occasions of Identity. Oxford, Clarendon Press.
  • McDaniel, K. 2004. Modal Realism with Overlap from Lewisian Themes: The Philosophy of David K. Lewis ed. Frank Jackson and Graham Priest. Oxford, Clarendon Press.
  • Sider, T. 2001. Four-Dimensionalism. Oxford: Clarendon Press.
  • Thomson, J. 1983. Parthood and Identity Across Time. The Journal of Philosophy 80:4, p. 201-20.
  • van Inwagen, P. 1981. The Doctrine of Arbitrary Undetached Parts. Pacific Philosophical Quarterly, 62, p. 123-37.
  • Zimmerman, D. 1993. Persistence and Presentism. Philosophical Papers 25:2, p. 115-26.

A collection of essays on persistence and temporal parts is:

  • Haslanger, Sally & Kurtz, Roxanne Marie. 2006. Persistence: Contemporary Readings. The MIT Press.
A series and B series

In philosophy, A series and B series are two different descriptions of the temporal ordering relation among events. The two series differ principally in their use of tense to describe the temporal relation between events. The terms were introduced by the Scottish idealist philosopher John McTaggart in 1908 as part of his argument for the unreality of time, but since then they have become widely used terms of reference in modern discussions of the philosophy of time.


An astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. It is an astronomical clock.

B-theory of time

The B-theory of time is the name given to one of two positions regarding philosophy of time. B-theorists argue that the flow of time is an illusion, that the past, present and future are equally real, and that time is tenseless. This would mean that temporal becoming is not an objective feature of reality.

B-theory is often drawn upon in theoretical physics, and in theories such as eternalism.


Chronometry (from Greek χρόνος chronos, "time" and μέτρον metron, "measure") is the science of the measurement of time, or timekeeping. Chronometry applies to electronic devices, while horology refers to mechanical devices.

It should not to be confused with chronology, the science of locating events in time, which often relies upon it.

Common year

A common year is a calendar year with 365 days, as distinguished from a leap year, which has 366. More generally, a common year is one without intercalation. The Gregorian calendar, (like the earlier Julian calendar), employs both common years and leap years to keep the calendar aligned with the tropical year, which does not contain an exact number of days.

The common year of 365 days has 52 weeks and one day, hence a common year always begins and ends on the same day of the week (for example, January 1 and December 31 fell on a Sunday in 2017) and the year following a common year will start on the subsequent day of the week. In common years, February has four weeks, so March will begin on the same day of the week. November will also begin on this day.

In the Gregorian calendar, 303 of every 400 years are common years. By comparison, in the Julian calendar, 300 out of every 400 years are common years, and in the Revised Julian calendar (used by Greece) 682 out of every 900 years are common years.

Counterpart theory

In philosophy, specifically in the area of modal metaphysics, counterpart theory is an alternative to standard (Kripkean) possible-worlds semantics for interpreting quantified modal logic. Counterpart theory still presupposes possible worlds, but differs in certain important respects from the Kripkean view. The form of the theory most commonly cited was developed by David Lewis, first in a paper and later in his book On the Plurality of Worlds.


Endurantism or endurance theory is a philosophical theory of persistence and identity. According to the endurantist view, material objects are persisting three-dimensional individuals wholly present at every moment of their existence, which goes with an A-theory of time. This conception of an individual as always present is opposed to perdurantism or four dimensionalism, which maintains that an object is a series of temporal parts or stages, requiring a B-theory of time. The use of "endure" and "perdure" to distinguish two ways in which an object can be thought to persist can be traced to David Lewis.


Eternity in common parlance is an infinitely long period of time. In classical philosophy, however, eternity is defined as what exists outside time while sempiternity is the concept that corresponds to the colloquial definition of eternity.

Eternity is an important concept in many religions, where the god or gods are said to endure eternally. Some, such as Aristotle, would say the same about the natural cosmos in regard to both past and future eternal duration, and like the eternal Platonic forms, immutability was considered essential.

Event (philosophy)

In philosophy, events are objects in time or instantiations of properties in objects.


In philosophy, four-dimensionalism (also known as the doctrine of temporal parts) is an ontological position that an object's persistence through time is like its extension through space. Thus, an object that exists in time has temporal parts in the various subregions of the total region of time it occupies, just like an object that exists in a region of space has at least one part in every subregion of that space.Four-dimensionalists typically argue for treating time as analogous to space, usually leading them to endorse the doctrine of eternalism. This 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. As some eternalists argue by analogy, just as all spatially distant objects and events are equally as real as those close to us, temporally distant objects and events are as real as those currently present to us.Perdurantism—or perdurance theory—is a closely related philosophical theory of persistence and identity, according to which an individual has distinct temporal parts throughout its existence, and the persisting object is the sum or set of all of its temporal parts. This sum or set is colloquially referred to as a "space-time worm", which has earned the perdurantist view the moniker of "the worm view". While all perdurantists are plausibly considered four dimensionalists, at least one variety of four dimensionalism does not count as perdurantist in nature. This variety, known as exdurantism or the "stage view", is closely akin to the perdurantist position. They also countenance a view of persisting objects which have temporal parts that succeed one another through time. However, instead of identifying the persisting object as the entire set or sum of its temporal parts, the exdurantist argues that any object under discussion is a single stage (time-slice, temporal part, etc.), and that the other stages or parts which compose the persisting object are related to that part by a "temporal counterpart" relation.Though they have often been conflated, eternalism is a theory of what time is like and what times exist, while perdurantism is a theory about persisting objects and their identity conditions over time. Eternalism and perdurantism tend to be discussed together because many philosophers argue for a combination of eternalism and perdurantism. Sider (1997) uses the term four-dimensionalism to refer to perdurantism, but Michael Rea uses the term "four-dimensionalism" to mean the view that presentism is false as opposed to "perdurantism", the view that endurantism is false and persisting objects have temporal parts.


HD2IOA is the callsign of a time signal radio station operated by the Navy of Ecuador. The station is located at Guayaquil, Ecuador and transmits in the HF band on 3.81 and 7.6 MHz.The transmission is in AM mode with only the lower sideband (part of the time H3E and the rest H2B/H2D) and consists of 780 Hz tone pulses repeated every ten seconds and voice announcements in Spanish.

While sometimes this station is described as defunct, reception reports of this station on 3.81 MHz appear regularly at the Utility DX Forum.

Intercalation (timekeeping)

Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.

Mereological nihilism

Mereological nihilism (also called compositional nihilism, or rarely simply nihilism) is the mereological position that objects with proper parts do not exist. Only mereological simples, those basic building blocks without proper parts, exist. Or, more succinctly, "nothing is a proper part of anything". Mereological simples can be both spatial and temporal. Mereological nihilism also asserts that objects existing in time do not have any temporal parts.


The minute is a unit of time or angle. As a unit of time, the minute is most of times equal to ​1⁄60 (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a negative leap second, which would result in a 59-second minute, but this has never happened in more than 40 years under this system). As a unit of angle, the minute of arc is equal to ​1⁄60 of a degree, or 60 seconds (of arc). Although not an SI unit for either time or angle, the minute is accepted for use with SI units for both. The SI symbols for minute or minutes are min for time measurement, and the prime symbol after a number, e.g. 5′, for angle measurement. The prime is also sometimes used informally to denote minutes of time.

Olfactory tract

The olfactory tract is a bilateral bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain, including the piriform cortex, amygdala, and entorhinal cortex. It is a narrow white band, triangular on coronal section, the apex being directed upward.

It lies in the olfactory sulcus on the inferior surface of the frontal lobe, and divides posteriorly into two striae, a medial olfactory stria and a lateral olfactory stria. Fibers of the olfactory tract appear to end in the antero-lateral part of the olfactory tubercle, the dorsal and external parts of the anterior olfactory nucleus, the frontal and temporal parts of the prepyriform area, the cortico-medial group of amygdaloid nuclei and the nucleus of the stria terminalis.Destruction to the olfactory tract results in ipsilateral anosmia.


Perdurantism or perdurance theory is a philosophical theory of persistence and identity. The perdurantist view is that an individual has distinct temporal parts throughout its existence. Perdurantism is usually presented as the antipode to endurantism, the view that an individual is wholly present at every moment of its existence.The use of "endure" and "perdure" to distinguish two ways in which an object can be thought to persist can be traced to David Kellogg Lewis (1986). However, contemporary debate has demonstrated the difficulties in defining perdurantism (and also endurantism). For instance, the work of Ted Sider (2001) has suggested that even enduring objects can have temporal parts, and it is more accurate to define perdurantism as being the claim that objects have a temporal part at every instant that they exist. Currently there is no universally acknowledged definition of perdurantism. Others argue that this problem is avoided by creating time as a continuous function, rather than a discrete one.

Perdurantism is also referred to as "four-dimensionalism" (by Ted Sider, in particular) but perdurantism also applies if one believes there are temporal but non-spatial abstract entities (like immaterial souls or universals of the sort accepted by David Malet Armstrong).

Philosophical presentism

Philosophical presentism is the view that neither the future nor the past exist. In some versions of presentism, this view is extended to timeless objects or ideas (such as numbers). According to presentism, events and entities that are wholly past or wholly future do not exist at all. Presentism contrasts with eternalism and the growing block theory of time which hold that past events, like the Battle of Waterloo, and past entities, like Alexander the Great's warhorse Bucephalus, really do exist, although not in the present. Eternalism extends to future events as well.

Static interpretation of time

The static interpretation of time is a view of time which arose in the early years of the 20th century from Einstein's special relativity and Hermann Minkowski's extension of special relativity in which time and space were famously united in physicists' thinking as spacetime.

Essentially the universe is regarded as akin to a reel of film – which is a wholly static physical object – but which when played through a movie projector conjures a world of movement, color, light and change. In the static view our whole universe – our past, present, and future are fixed parts of that reel of film, and the projector is our consciousness. But the 'happenings' of our consciousness have no objective significance – the objective universe does not happen, it simply exists in its entirety, albeit perceived from within as a world of changes.

The alternative, and commonly assumed view, is that the world unfolds in existence, that our present has some wider physical significance, because the universe evolves in step with it.

The static view is the simpler in that all that is held to exist is the physical ordering of the universe. All that there is at every time simply exists. The unfolding view requires an additional quality to the universe – that besides the physical ordering there is some quality of coming into and out of existence.

One can argue that the onus is therefore upon those who propose it, that the world unfolds, and that this additional quality they hold to (absent from special relativity) is indeed a physical feature of the world. There is however as yet no proof, experiment, or measurement, to show that our conscious experience of an unfolding present has any objective physical significance, or that the universe is anything other than static.

The static view is however commonly rejected for psychological, not scientific reasons, because it leads to a fatalistic or "fixed" conclusion about human existence – our 'past', 'present', and 'future' being what they are – there is no contingency in the world and no possibility of 'altering' or creating the future through some act of will – the future exists. It is simply that our consciousness has not yet reached it.

Tomorrow (time)

Tomorrow is a temporal construct of the relative future; literally of the day after the current day (today), or figuratively of future periods or times. Tomorrow is usually considered just beyond the present and counter to yesterday. It is important in time perception because it is the first direction the arrow of time takes humans on Earth.

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