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William Ockham on Time
Medieval philosophers often thought of time as relative to motion. Even today we may wonder why we need to postulate time as a dimension, time as anything more than a measure of motion and change. Time for William Ockham is a measure of the duration of motion. It is worthwhile to note that Ockham suggests motion is not separate from objects. This is an attractive notion since we would no longer be concerned with time’s ontological status, as it is not separate from permanent things. Ockham argues that time and an instant are relative to the motion of objects. For him there is no need for absolute time separate from motion.
The first step in his critique concerns the instant. He argues against the opinion that an instant is a “certain flowing thing which is steadily destroyed, or lost, so that it does not remain.” (p. 91 Shapiro). Such that the present moment is destroyed by the new moment. He argues that in a finite section of time there would be an infinite amount of instants, due to time’s infinite divisibility. He further takes issue with the notion of an instant being destroyed. He points out that “since there has been no contrary introduced, and since the original cause is still active - nor can the subject of these absolute moments be said to have been destroyed - how can one explain the exorable passage out of being of absolute moment after moment?” (p.92 Shapiro). In other words, one instant and another instant are not opposites or contrary to each other in kind, such that one can destroy the other. Finally there is the problem that an instant according to Ockham cannot be adequately described as a substance or a quality. Therefore he does not believe in an absolute moment of time or that time is composed of instants.
He does not believe time can be understood as an entity streaming from the past to the future separate from permanent objects. Time is a divisible accident, for it is within a temporal body. Further being a divisible accident “time must have simultaneously existent parts to account for its extended and divisible character - but Aristotle expressly denied the simultaneity of the parts of time.” (p.94 Shapiro). Conversely, other theorists suggest “that time’s extended character is owing to successive addition of temporal to temporal part, rather than to their simultaneous existence.” (p.94, Shapiro). The idea of temporal parts according to Ockham is still at odds with Aristotle, “since the temporal subject which time is posited to be in is extended by means of simultaneously existent, extended, parts, hence time - a quality investing this object - must be conceded to consist in simultaneously existent parts.” (p.94 Shapiro). Time he concludes cannot be distinct from permanent things, otherwise it would be in simultaneously existent parts.
There are two methods of measuring, according to Ockham; there is the measurement by permanent things and the measurement by successive things. Time then is “’the measure of all things whose duration can be certified by the intellect by means of something else better known to it,’” (p.97 Shapiro). Thus the most precise measurement of time would then be based on the movement of something permanent. It is “the ordered, progressive, natural sequence of motion, Ockham contends, which allows us to cognize, and employ as a measure, its temporal dimensions.” (p.97 Shapiro). Therefore it is not that we are in time and measure motions with each passing moment, rather, time itself is taken from movements of objects and thus measured. The relatively uniform movements of the sun do provide a useful reference for time, however, for Ockham, it is the heavenly spheres that would be more accurate. A moment of time conceived by Ockham then is “a translation into temporal terms of the spatial changes suffered by the sphere of the fixed stars.” (p.100 Shapiro).
The notion of time based on the measurement of a consistent motion recognizes how we commonly conceive of time. The difference being we generally feel we are in time, feel the flow of the moment, rather than time being in objects and simply a measure of their motions. Nevertheless, a day and a year are measured by the earth’s rotation and orbit around the sun. However, in modern times we do not have the perfectly uniform movements of the heavenly spheres in which to create a specific measure of time, but we do have motions we consider to be far more precise such as the decay of certain particles. This still provides us with a common understanding of a scale of time based on relatively uniform movement, which is then further used to measure other movements. Time as a measure of movements or change feels intuitively correct. Each change creates a new now, where the past temporal part of an object no longer exists nor does the future part yet exist. There is no time outside of change and motion within objects.
One objection raised by his contemporaries was that if there were many heavens, many permanent spheres, there would be many times as well. For Ockham this does not present a problem at all, since all times would be equivalent to one verifiable, knowable and functional measure of time.
Another objection rises from the fact that, for Ockham, motion and change are shown to be individual motion and change within objects, with no absolute time outside of objects themselves. And yet time is identified with the one motion of the spheres. His response being that time is through which all things are measured, with regards to their motions and rest. Therefore time can be claimed to be in particular things because they have motions and changes that can be measured.
A third concern is that motion can be fast or slow but time is considered to be the uniform measure on which to verify that fact. Therefore it seems odd to say time is motion when time cannot be understood to be fast or slow. Ockham points out that not all motions are times and the terms are not interchangeable. The events being measured by time have varying durations, while the measure itself is consistent in nature. Time itself is a motion, “but a motion of such rigorously constant velocity as to be normative for the entire universe.” (p.106 Shapiro).
The final objection pertains to different conceptions of the instant. An absolutist would say time is divisible and must have more than one terminus, since an instant is a terminus of time, time must be composed of many instants. Ockham does not see an instant being an atomic thing in itself but rather understood as the successive changes in position of the spheres. The ‘now’ of the instant merely states the current position of the spheres, or prime mobile.
It seems for Ockham if there were no motion there would be no time. In fact, all that exists for Ockham is the present moment and that exists in present objects. This itself can be seen to be a problem since we might want to say an instant is the link between the future and the past. If time is just a measurement of motion, not separate from objects, then what links past changes, to current states and future states? In other words, how can motion be understood to be successive in nature? Since only the present exists then from motion to motion there must be instantaneous change. The present instant being the only existent thing, and not separate from objects. Some would say without things in time, things with temporal parts, there would be no way to link future parts, to present parts, to past parts. Presentism therefore has a problem with causal links since the cause is no longer existent to produce the effect, therefore from instant to instant all of the world could dramatically change. Which is not a problem at all if motion and change are considered to be fundamentally instantaneous. And time being a measure placed on successive changes by beings that perceive change.
For some, however, it seems an instant needs to be a link between parts of time and temporal parts of things rather than an atomic static entity. Since, for a presentist, the ‘now’ would indeed be static. There is no motion or change in an instant. In order to have continuous movement we need to have something to combine those successive states of change, whether it is absolute time, the nature of motion itself or something particular to permanent objects. Since for a presentist time is non-existent they must take a stand on the nature of change itself to show how one current state leads to another current state. Or we could conceivably have a universe where from one moment to the next everything remains static for long durations before moving again and no one during this frozen period would be aware of the passage of time at all. If an instant is merely reflecting the place of the spheres in the ‘now’ then an instant is just a slice of motion. Instant to instant, is a slice of motion to motion, like frames in a film. Only when the film is played do we have what we would call motion and consequently time. Inadvertently we end up with a non-fluid notion of time, more like instantaneous position to position. Without absolute time and without objects having temporal parts we must have a way to describe how one static instant is linked to another.
One solution to this problem is to state there is real motion and change. We could further claim that it is the particular nature of objects in motion that the immediately prior and posterior motions are entailed in the present moment, leading to a continuity between instants. Thus the present instant is not some absolute unit of time but a flimsy link connecting echoes of past motions and stretching out to possible future motions. This solution is much like trying to save a distinct time by postulating that the “present instant is that through which the past is continuous with the future the way a line is continuous through its midpoint, cannot the whole of time ‘borrow’ some existence from the present instant?” (p.858 McCord). This solution which Henry of Ghent uses is criticized by Ockham: “that whereas all the parts of a line are actual and combine to make something per se… not all parts of time or motions exist in themselves. So while there is nothing in reality that actually divides a given line or surface, there is something in reality that distinguishes one instant from another and from various parts of time.” (p.860 McCord).
Or, more plausibly, we could claim all motion is in nature a change, and like Ockham agree that change is not successive but instantaneous. If it is instantaneous, then there is no need to posit absolute time. When these instants are linked we perceive motion and can measure time. Under this scenario there would be objects that endure and can be permanent. They simply are not perceived to change moment to moment and can appear to have duration compared to objects with obvious and predictable changes. Although what we would be saying is that there can be no time without change. Ockham would say however, objects always at rest cannot be measured by time, but it does seem we can use the same standard of measure, that which we gain from known objects that move in a predictable fashion, to refer to objects of this sort or we could say that change is a fundamental property to objects, not time being a property of objects in motion. However we look at time as a measure of motion, rather than absolute time, we are faced with limitations on how we view temporal objects, motion and change itself.
McCord, Marilyn William of Ockham
Shapiro, Herman Motion, Time and Place According to William Ockham