Time

Encountering Philosophy, Chapter 20

Travis Joseph Rodgers

In his Physics, Aristotle asks whether time exists and what it is like (217b). These are questions philosophers still discuss, but they have further clarified the questions. Is time real? Is it somehow objective or subjective? Is it, in other words, “out there” to be discovered or is it a product of the (human?) perceptual apparatus? There are two major rival accounts of what time is like. Time may flow like a river, or it may grow like a snake in the arcade game Snake.

General Characteristics

Time may be one of the preconditions of any human experience. What would a human experience be like without space or time? Time is certainly subjective in the sense that subjects experience time (cf. Kant). Is it also somehow “out there” and independent of our experiences? Here’s one way it could be. Time, in Aristotle’s estimation, is an accident (Categories). That means it’s something that depends for its existence on other things, things he calls substances. Because there are things like humans and cats that persist, gain and lose attributes, there is time. So, on Aristotle’s view, time is not just a necessary aspect of how we perceive. Although time cannot exist without some substances that exist, it is there regardless of whether it’s perceived.

A-Sequences and B-Sequences

There are, John McTaggart wrote, two sorts of "positions in time." According to one type of sequence, some event can be past, present, or future. According to the other, some is earlier than another or later than another (458). The first sorts of positions are impermanent. Consider an example. There's an event in which Travis sits and types an article on Time. There's an event in which Travis decides to sit and type an article on Time. As I type this, one of them is present, and the other is past. Sequences that include past, present, and future, McTaggart calls A-sequences.

The second sorts of positions are permanent. The event in which Travis writes is later than the event in which Travis decides. And the events are always related in that way. McTaggart would call this a B-sequence. It's difficult to talk about time, especially in the Western philosophical tradition, without appeals to these sequences. They form the basis of discussion on time since the early 20^th century. So, let’s explore them in a bit more detail.

A-Theory

According to the A-Theory of time, time flows like a river (Jubien 16). Times that were we call the past. The time that is we call the present. And the time that will be, if there is such a thing, we call the future. On this view, the present is the only time that actually is or exists. The others did exist or will exist, but they don’t now exist. Thus, A-Theory privileges the present; hence, it is sometimes called Presentism. A-Theory gets its name from ordering events as in an A-sequence.

Time, on A-Theory, has a direction. It flows in only one direction, with the past framing and at least partially determining the present. Similarly, the present at least partially determines the future. Causation, it might seem, can work only in the same direction as time. Causes precede effects. So far, this may sound plausible. But A-Theory is not free from challenges.

If the present is the only time that exists, how do we make sense of claims about the past or future? Some of them seem to be true. “I was a baby,” for instance, could be true, even in 2025. By privileging the present, we face the difficulty of explaining how a past that is no longer real nonetheless grounds the truth of claims. Nina Emery (2017) notes the challenges. Things that no longer exist somehow enter relations with existing things (I like Socrates) and they somehow make claims true (Dinosaurs roamed the earth). That’s strange.

B-Theory

Perhaps some of those concerns about A-Theory motivate an alternative picture of time. B-Theory views time as consisting in B-sequences. Just as some things are taller than others, some events are prior to others. These relations produce a four-dimensional picture of things. Just as objects have length, width, and height, they also have temporal parts.

Some of these temporal parts precede others. There is, for instance, a Travis-part at some earlier time, say yesterday, that we can call T1. There is another Travis-part right now, as I type this, at T2. Travis is never fully present, as he is, at all times, according to A-Theory. Rather, Travis has temporal parts, and he is present only collectively by summing all those parts, on B-Theory.

This view of time gives rise not to the flowing river image of A-Theory but rather to an image familiar to those of us who grew up on arcade games. In Snake, the player controlled a snake that moved constantly. When it encountered a pellet, the snake would grow by one block in length. The goal was to make the longest snake possible without crashing into a barrier. A being like Travis is like this sort of Snake. As we discover that Travis is in more temporal units, we see just how large he is, temporally.

All this talk of temporal parts sounds like it still requires a present, a future, and a past. How does the B-theorist avoid these “tenses”? B-theory makes use of “tenseless” propositions to explain the world. “Travis is 9 pounds, 12 oz. on April 17, 1979,” is true, and so is, “Travis is 150 pounds on June 17, 2025.” By including a time in the claim, no (further) tenses are necessary. These claims are either true or false always, and there is no need to appeal to things that used to exist or will exist in the future.

Aristotle. Categories.

Aristotle. Physics.

Emery, Nina. 2017. “Temporal Ersatzism.” Philosophy Compass.

Kant, Immanuel. Critique of Pure Reason.

McTaggart, John Ellis. 1908. The Unreality of Time. Mind.