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New essay: An Introduction to the Philosophy of Time

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By Robert P. Taylor (2007)

It would not be amiss to compare the mystery of time with the mystery of the divine (should any such thing exist). On the one hand, it seems everyone is aware of it. The transition from morning to afternoon conveys a sense of time. The ongoing aging process conveys a sense of time. Change, or rather the perception of change, conveys a sense of time. Yet, in spite of all this, and when even the simplest and the most brilliant minds agree that there is at least an inference of what might be called ‘time’, it is not at all apparent what time is. More interestingly still, it is not at all obvious that time itself even exists.

The Non-Existence of Time

It is not uncommon for philosophers to use spatial analogies when describing issues relating to time, and I think one would be apt here. Consider that there is a room with no doors and a small window looking in. When you look through the window, you see a red cube; and yet, you later discover, the cube is not there at all. What is there is a trick of the light - a result of mirrors and infrared light-waves and a host of other things that create the illusion.

From the experience, two things should be clear: first, it is obvious that there is no actual red cube; and second, if there is no red cube, then there must exist some sort of entity that is capable of producing the illusion of a red cube. At the macroscopic level, and by ordinary experience, the illusion of an object is bound to the same physical laws as an actual object. Hence, if there is nothing to determine the existence of the object (mass of particles formed in such a manner as to create a solid, liquid or gaseous form of certain size, shape and structure) then there is no object. Likewise, if there is nothing to create the illusion of an object (refracting or reflecting light-waves, distorted light-beams, hallucinations caused by psychological defects, et cetera) then there is no illusion. As it were, nothing comes from nothing.

As to space itself, Solipsists contend that the world is illusionary: it does not exist, at least not as perceived. Taking this to the extreme level, one might assert that space is not real, and this would apply whether space is a substance or a relation between spatial objects. If space is a substance, then the laws of illusion apply to it as well as to spatial objects: something creates the illusion. It might be cognitive processes going on in a brain imprisoned in a vat, or it might be an elaborate computer code. On the other hand, if space is a relation, then the exposé of spatial objects as illusions themselves should be enough to deal with the apparent existence of space. Quite simply, there cannot be an existing relation between two non-existent objects. As with spatial objects, the illusion is there because it has a source. Either the thing that makes one perceive spatial objects is the thing that makes people perceive space, or space is a coincidental consequence of the perception of spatial objects.

For example, in the room with the red cube, suppose that another object – also an illusion – exists. Anyone looking through the window will perceive a red cube and (say) a blue cube. One will also perceive a fixed distance between the two cubes. When the illusions end, the distance will no longer exist, because distance, being relational, requires spatial points to relate to. If there are no cubes, there cannot be distance between the cubes.

What about time? Is the illusion of time possible even without a source for the illusion? If so, then one must ask what the illusion is. How do we differentiate between actual time and perceived time, if either of them exist? If we cannot differentiate, how can we say time is illusionary? On the other hand, if there is a source for the illusion of time, what is its nature? Is there a super-time so beyond human comprehension that a simpler form of time is required? Is time the consequence of a fallible perspective of reality? Is it necessary to posit entities or phenomena to explicate time?

Already, just by asking if time exists, I have been forced to compare time with space and ask, if time does not exist, what gives us the perception of time? If time is real, what is it? If time is not real, what do we perceive, and is that thing externally located or internally located? If it is internally located, does it bear relation to external entities or phenomena, or internal brain states? If it is externally located, is it spatial, or does it stem from something altogether unfamiliar? These are the sorts of questions asked by philosophers interested in the subject of time.

A- and B-Theories

The A-theory, put in simple terms, states that time flows. The theory also states that there are tensed propositions relating to unfixed temporal points. That is, there is a past, there is a present, and there is a future.

What exactly is meant by the proposition "time flows" is a complicated issue, and some philosophers would even reject the notion of the flow of time as ridiculous: if time does flow, then how fast does it flow? A second per second? A second per supersecond?

With the A-theory, truth-apt statements such as "Hitler stole power in the past", "I am typing an essay about time now" and "There will be a seminar on Quantum Existentialism in the future", have their truth values determined by their position in the time-line. That is, the state of a proposition is determined by its referent being in the past, or in the present, or in the future.

The B-theory states that time does not flow, and that time is tenseless. The implication of this is that there is no past, no present and no future. That is not to deny any of the events in time; rather, it is to claim that "past", "present" and "future" are indexicals. Points in time are more like "here" and "there" than fixed geographical locations like "Liverpool", "New York" or "Melbourne".

According to B-theorists, the proposition "In the past, Hitler stole power" would actually mean "At some point in time prior to the one I presently occupy, Hitler stole power", and "I am typing an essay about time now" would actually mean "From my perspective I am now typing an essay about time". However, it would not be contradictory to say "Hitler is now stealing power and I am now typing an essay", given that the scope of "now" is not constrained to any one perspective. In other words, in relation to my position in the time-line, Hitler is not now stealing power, and in relation to his position, I am not now typing an essay. In a similar sense, a person in Manchester is "here" as much as a person in Liverpool is "here", but neither one of them could honestly say "We are both here", for the referent of "here" is not identical in both cases.

The A-theory, and the B-theory, are often confused with related theories. Perhaps this confusion is down to a subconscious insistence that a theory needs to be complete, and that neither the A-theory nor the B-theory are complete. Perhaps the confusion stems from the fact that many ideas relating to time potentially overlap, or are contrary to one another. Since, for example, Presentism makes claims contrary to claims of the B-theory, it is understandable that Presentism might be confounded with the A-theory. Likewise, since the B-theory is often explained with spatial analogies, and since Four-Dimensionalism goes some way in making such analogies less unclear, it is understandable that the B-theory might be confounded with Four-Dimensionalism. I will now look at each of these in turn.


Four-Dimensionalism may refer either to the view that time consists of real parts, like spatial parts (this contrasts with such views as Presentism), or to the view that spatial objects have temporal parts (such that the objects are extended through time, as well as through space). For the purposes of this essay, the view that time consists of real parts will be referred to as Eternalism, while the view that objects have temporal parts will be called Perdurantism. One should note that Four-Dimensionalism is not identical with the B-theory, though the two are compatible.


Eternalism states that, just as all spatial points are equally real, so too are all temporal points equally real. This view is compatible with both the A-theory and the B-theory.

Under A-theoretic Eternalism, an event in the future will flow from future, to present to past. It exists in all three temporal states – what that means, exactly, is unclear – rather than coming into existence in the present. For example, consider that a sprinter is being observed running past a slit in a wall. The observer can only see a slice of the racing track. As the sprinter passes the slit, the observer sees the sprinter, but the sprinter exists on the track even when he is not being observed. Obviously this analogy does not distinguish between past and future events, but it is sufficient to differentiate Eternalism from the view that only present events exist.

Under B-theoretic Eternalism, all moments are equally real, and have equal validity in terms of their status as a temporal frame of reference. This contrasts with A-theoretic Eternalism, which contends that past and future events are real, but have a less valid reference frame than present events. Often, Eternalism is simply equated with the B-theory, since both theories present a view of time that grants equal ontological status to all temporal points. Furthermore, it is not obvious what an Eternalist A-series would entail. What does it mean to grant equal ontological status to the past, the present, and to the future, but give ontological importance to the present? This question has been explored in philosophy, though not always (if at all) successfully.


In brief, Presentism contrasts with Eternalism, in that where Eternalism posits existing temporal moments beyond the present (such that the past and/or future exist in addition to the present), Presentism posits that only the present exists.

An A-theorist Presentist might state that time flows: a potential future moment t3 becomes an actual present moment t2, and then a conceptual moment t1. This t3 is potential: it has the potential to become an actual moment. For instance, a driver speeding towards a wall will either crash or will not crash. Both the crash and the aversion of the crash are potential moments in the future. The t2, being present, is an actual moment. For those who understand Modality, t2 exists in the actual world; it is real. Therefore, the driver may crash. The event of the driver crashing into the wall is an actual present moment. The t1 is, for lack of a better term, a conceptual moment; it does not actually exist (any more) but can be conceived through memories, historical documents, and the like. One may thus remember being in a car crash. This memory is a conceptual representation of a moment that did exist, but does not now. The flow of time, then, is the passing of temporal points in and out of actuality.

It might be objected that the potential future and the conceptual past have no place in the ontology of a Presentist. However, Presentism does not need to abandon any of its premises to acknowledge the existence of potential/conceptual temporal moments. All that needs to be done is to establish that the past and the future do not have the same ontological status as the present. The future can, perhaps, be foreseen. The past can be remembered, but these are no more real than a notion of an object being as real as the object being thought of. That is, representations of the past, and of the future, can certainly exist without contradicting Presentism.

I have distinguished between past and future moments as "potential" and "conceptual" moments. However, some cases suggest such terms cannot be so readily applied. Fatalism, in conjunction with the notion of accurate prediction (e.g. infallible foreknowledge), would make the future conceptual, rather than potential. Likewise, backward causation or backward counterfactual agency could make the past potential, rather than conceptual.

[A brief note: counterfactual agency takes the logical form "If P had occurred, then Q would have occurred". The antecedent of a counterfactual conditional necessarily involves some event that did not occur, but could have. Therefore, "If Hitler had not invaded Russia, he would have taken Europe" would be a counterfactual.]

It is apparent that no B-theorist can adhere to Presentism, since by its nature the B-theory denies the existence of the present. Certainly, denying the status of "present" to what we experience to be "now" would not work, because without some other time to reference, "now" would not be "now" indexically, and this is precisely what the B-series depends on. It makes no sense to deny status of present to a point in time that has ontological precedence over other points in time.


Endurantists maintain that objects simply are three-dimensional entities extended through the three dimensions of space. Further, objects persist through time in that one is wholly located at some point in time (t1), and passes to other points in time as a whole entity.


Perdurantism states that objects extend through the three spatial dimensions, as well as through a fourth dimension. Therefore, objects have both spatial and temporal parts. This means that while a temporal part of an object may exist at t1, a distinct temporal part exists at t2, and another temporal part exists at t3, which is distinct from the temporal parts that exist at t1 and t2.

Perdurantists can be divided into two main subclasses; viz. Worm Theorists and Stage Theorists (Exdurantists). Worm Theory states that temporal parts are segments (analogous to segments of a worm). If one imagines the entirety of an entity as a worm extending from future to past, then each segment of the worm would be a temporal part, suspended in a temporal moment. Stage Theorists hold that each temporal part of an entity is, in fact, a temporal counterpart to the same entity. Consequently, an entity, under Exdurantism, exists only during a single moment. In the next moment, a different, but identical entity exists as a counterpart.

Exdurantism is a relatively novel theory, which appears to be an attempt to reconcile Endurantism with Perdurantism, by positing temporal counterparts rather than temporal parts per se.


With this section of the essay, I hope to have provided the reader with a basic overview of some of the ideas tackled by philosophers interested in the metaphysics of time. Consideration, and indeed, discussion of these ideas is to be encouraged, and suggestions for research are always welcome.

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