International Catholic University
In our last lecture we developed an epistemic model to assist our understanding of natural kinds and how these kinds give rise to characteristic activities from within themselves. Nature, as we have seen, is the basic principle of operation within natural substances, and it exhibits itself in two ways. First, it presents itself as an active and actualizing principle within the substance, which we recognize as a form and which we call its substantial or natural form. Second, it presents itself as a potential and conservation principle, which we recognize as matter, a basic material stuff within the substance which we call prime matter or protomatter.
In developing our model we proposed to model natural form as an energizing field, taking inspiration from modern robots, which can simulate nature's functions when they are properly energized. The natural form energizes protomatter, which in itself lacks all distinctive attributes, and so we represent it as a circular field expanding out from a central point. The point represents protomatter, which may be thought of as the opposite of a black hole from which the natural form emerges. And within this energizing field we situated the powers that are proper to, and indicative of, a particular natural kind.
In modeling an inorganic nature -- as studied, for example, in physics and chemistry -- we simply appropriated the four basic forces found in the physical universe. These are the powers we now use to explain the activities and reactivities of non-living substances. We arranged them symmetrically within the field, since they are actually powers of the nature as natural form. They are usually enumerated, with their symbols, as the electromagnetic force (EF), the gravitational force (GF), the weak force (WF), and the strong force (SF).
At the end of the last lecture we promised to augment this model of inorganic nature so that it could also be applied to two additional genera of natural kinds, those of plants and animals. Just as we used four powers to explain the properties of inorganic natures, we shall find that four additional powers each suffice to characterize plant natures and animal natures.
Plant natures -- as studied, for example, in botany -- are obviously more complex than inorganic natures. Apart from their atomic and molecular parts they are organisms with their own systems and functions to account for. Aristotle was aware that plant organs exercise three basic powers that are required for life processes. These he enumerated as nutrition, growth, and reproduction. Modern biologists would add to these homeostasis, the power whereby an organism maintains its stability while adjusting to the environment in ways that are best for its survival. With this addition we have the four powers required for plant life. Adapting to modern usage, we shall change their names slightly from those used by Aristotle.
I am using graphical aids throughout these lectures that are available to those taking the course for credit. Some of the figures are found in my The Modeling of Nature, published by The Catholic University of America Press in 1996. We enumerate these four powers, with their symbols, as shown in Fig. 4.1 (p. 95 in Modeling of Nature): the homeostasis control (HC), the metabolism control (MC), the developmental power (DP), and the reproductive power (RP). These, then, are the four basic vegetative powers. They must be added to the four inorganic powers we have already enumerated to provide a total of eight powers to account for all the activities of a plant form.
Figure 4.1 diagrams the powers model of a plant nature. Like that for an inorganic nature, it starts with a point source, labeled PM for protomatter, as heretofore. This is surrounded by an energizing field that radiates from it and constitutes the plant organism -- now labeled NFp, for natural form, with the subscript "p" designating plant. Within that field, as before, the eight powers are arranged symmetrically, but also hierarchically, with the inorganic powers in the lower hemisphere, the organic powers in the upper.
Notice the up and down arrows on either side of the letters PM, connecting the two sets of powers and showing the interchanges between them. These have a slightly different function from the arrows we have used previously in the inorganic model. Our earlier use of arrows represented activities that originate or terminate outside the substance being modeled and on this account are called transient actions. As opposed to them, the up and down arrows on either side of the PM designate immanent actions, those that remain within the plant and are perfective of it. Plants also initiate a few transient activities, as can be seen from the single arrow emerging from the reproductive power, when it produces seeds and brings into being a new organism of its own species. Also the two reciprocating arrows attached to the box for homeostasis show that it controls environmental reactions with substances that exist outside the plant.
The function of the plant form NFp with respect to the inorganic powers in the lower part of the model is obviously different from that of the inorganic form NFi in the non-living. The atomic and molecular structures these powers control are now part of the plant, and they are regulated by the form (mainly through its metabolism power, MC) to meet the energy requirements of the plant's life. The natural form NFp further determines the way in which this nutritive energy is used, through its developmental power DP, controling the distinctive patterns in which the plant grows and stops growing. And finally, the natural form channels energies of the adult form, over and above those required to sustain its own life, through its reproductive power (RP), for the generation of new organisms.
As in the case of inorganic natures, the generic power form is not sufficient of itself to model a specific plant nature. To this has to be added iconic models that portray in detail plant structure and functioning. These are different, for example, in algae, fungi, mosses, and vascular plants. Each of these phyla has its characteristic root, stem, and leaf systems, and uses them in various ways for transpiration and reproduction. These have been understood and sketched by botanists for centuries, but with the development of biochemistry in recent decades, much more is known about metabolism and replication. Graphic modeling techniques make these life processes interesting and intelligible even to those who have little formal education in the sciences that specialize in them.
From this you get the basic idea of a generic powers model and the way it can be used with iconic models to gain an insight into natural forms of the organic and inorganic types. As we move up the scale into the animal kingdom the powers of the natural form become more complex. Animals differ from plants basically in two respects: they possess knowledge of objects external to them, and they are able to move locally, typically from place to place. For these they require four new series of powers. We shall enumerate them, with their symbols, as shown in Fig. 4.2 (p. 105 of Modeling of Nature): the outer senses (OS), the inner senses (IS), the motor powers (MP), and the emotional reactions (ER). These should be familiar to you, for we have already discussed some of them in previous lectures.
Figure 4.2 builds on the materials provided in Fig. 4.1 to diagram these powers of an animal nature -- the type studied by zoologists. Now we have, in addition to the four inorganic powers and the four vegetative powers, the four basic powers of sensitive organisms, for a total of twelve. These are again arranged hierarchically, with the inorganic powers at the bottom, the vegetative powers in the middle, and the sensitive powers at the top.
Animal organisms are receptors and initiators of transient actions. This can be seen in the top set of boxes -- with the inwardly directed arrow on the outer senses (OS) box and the outwardly directed arrow on the motor powers (MP) box. They also manifest more immanent action than plants. This should be obvious in the arrows connecting all four of the sensitive powers internally, showing how each influences and is influenced by the others. Immanent action is also seen in the two pairs of up and down arrows below and above the middle set of powers. As in the case of the plant form, the pairs of arrows are meant to show the relationships among all twelve powers of the three sets. The lower pair indicates how the four powers of the inorganic subserve the four plant powers. The upper pair show how the plant powers in turn subserve the needs of animal life. Viewed in another way, the four sensitive powers of the animal kingdom require all eight powers of the vegetative and mineral kingdoms for their proper operation. The ensemble of these powers operating within the animal is what constitutes its nature or specifying form. This, as previously, is modeled by the radiating circles or field labeled NFa, with the subscript "a" meaning animal. This natural form energizes all the powers and enables them to function as a specific organic unit. As before, it is the ontological correlate of protomatter (PM), shown at the center of the figure.
To understand Fig. 4.2 fully it must be associated with an organism of a particular species, say, a squirrel. A live, adult squirrel is able to exercise all of these natural powers, and it does so in ways that contribute to the unity and well-being of the entire organism. Its life has an inorganic base in the sense that its bodily components obey all the laws of physics and chemistry. It also is able to provide its own vegetative functions -- it assimilates its food and grows and develops, and eventually procreates its own kind. All of these functions then undergird its sensitive and mobile capacities.
There are, of course, many more species of animals than there are of plants. The two major divisions are the invertebrates and the vertebrates, the second including all the fishes, amphibians, reptiles, birds, and mammals we commonly call animals. All of these have distinctive organ systems for carrying out the activities they share with plants as well as those that are properly their own. And many of these functions can be modeled and understood in terms of iconic models, as in the case of robots used to emulate animal activities.
It is important, however, to remark on an important respect in which a natural squirrel differs from a robot. The natural squirrel is self-developing and self-activating -- another way of saying that it is alive. Robots work only when they are externally powered or energized. The squirrel is energized by nature. And yet the concept of being energized casts light on the function of the natural form in the realm of the living. Just as a robot is inert or dead when it lacks a source of energy, so the squirrel is dead when it is no longer animated. Then it no longer has its nature. Then the powers deriving from that nature are inoperative. Its structure disintegrates and the organism itself decomposes into inert chemical substances.
With this we are in a position to examine the major property of natural beings, the property that differentiates them from mathematical beings and incorporeal beings, that is, their ability to undergo change. Another way of saying this is that the subject of natural philosophy is moveable or changeable being. In Aristotle's vocabulary the same term was frequently used for motion and change. So when he defined nature as a "principle of motion and rest," he used the word "motion" to refer to all changes that take place from within a natural body. And he himself points out, at the beginning of the third book of the Physics, that "if we are ignorant of what motion is, we are of necessity ignorant of what nature is." Hence the importance of being clear on what we mean by the term motion.
From the materials we have just covered on inorganic, plant, and animal natures, it should be obvious that natural kinds undergo many types of changes or motions. The most obvious motions are the change of place of a falling body, the change of size of a growing plant, the changes of color in a plant's leaves or fruit, and the various movements of animals, from the flight of the bird to the leap of the jaguar. There are also the substantial changes we have been illustrating in physics and chemistry -- the generation of salt from sodium and chlorine, the decomposition of water into oxygen and hydrogen, and the radioactive breakdown of uranium to lead.
To put some order into our discussion, let us note that the English word "motion" can be taken either in a strict sense or in a wide sense. In a strict sense it has the same meaning as the Greek kinesis and the Latin motus, from which the English motion obviously derives. In a wide sense it can be extended to include also the meaning of the Greek metabole and the Latin mutatio, which may be translated as mutation or change. In what follows we shall focus on the first or stricter meaning -- we shall take motion to mean a movement that can be perceived by the senses, that is successive and continuous, and that takes place in time. This definition would apply to the fall of a heavy body, the growth of a plant, the change in color of its leaves, and the various movements of a squirrel's body.
Notice that there is one type of change we have already considered that is not included in this stricter meaning. I refer to change of substance -- substantial change, that from one natural kind to another. This type of change is recognized by the intellect, but it is not directly perceived by the senses. Or, to put it another way, it is seen by us as instantaneous. First we have water, then we have oxygen and hydrogen. Water ceases to be, there is a transition from being to non-being; oxygen and hydrogen come to be, there is a transition from non-being to being. There is nothing intermediate beween being and non-being. We have tried to indicate this in modeling changes of this type by a pair or a series of parallelograms. In the case of the pair of parallelograms, there is a flip from one to the other, with protomatter anchoring the base and different natural forms immediately activating it. In the case of the uranium series of parallelograms, protomatter was the subject that was conserved throughout the radioactive breakdown, with different natural forms appearing successively. Protomatter was never without a natural form, always with some form or other, never in an intermediate state between being and non-being. A natural kind was always identifiable, and could be seen as uranium, thorium, protactinium, radium, or lead at each stage throughout the process.
Now we focus on motion in the first or strict sense as sensible and successive movement and consider how it may be defined. One of the easiest ways of defining an entity, for Aristotle, is to locate it in one or other category of being. We have enumerated his ten categories of being, and now find that it is no simple matter to situate motion in a particular category, since it is found in more than one category. Change is situated in the category of substance, but we have eliminated that because it is not sensible and successive motion. Yet change or movement in the sense we are now taking it is also found in the category of quantity, as in the growth of a plant or animal from small to large, in the category of quality, as in the change of color or temperature, and in the category of location, as in movement from here to there. What terms can be used to define a type of being that spans these three categories?
Aristotle's philosophy is distinctive in its treatment of this problem. Another Greek philosopher named Parmenides had denied that there could be any intermediate between being and non-being. Aristotle contested this view with a teaching we have already seen, namely, his teaching on act and potency. Between nothing and something in act, Aristotle maintained that there is a third possibility, namely, something in potency. We have used this concept in previous lectures when discussing protomatter as a type of potential being. We have used it also when discussing powers as abilities or potencies that are sources of activity in natural kinds. Aristotle's solution of the problem of motion was to situate motion midway between actuality and potentiality.
When a body is only in potency to a particular state, Aristotle reasoned, it is not yet in motion. When its potency to that state has been fully actualized, the motion has ceased. Therefore, motion consists of something in between potency and act. It is an incomplete act. But one has to be careful with the expression "incomplete act," because it may be difficult to see how an act can be incomplete. To remove the difficulty Aristotle thought it necessary to add, beyond the indication that motion is the incomplete act of being in potency, that the thing moved had to be still in potency to more and more of the same act. This line of reasoning led him to the classical definition: "Motion is the actualizing of what exists in potency insofar as it is in potency." The definition is difficult to understand, but let us break it down into three components: (1) motion is the actualizing (2) of what exists in potency (3) precisely as it is still in potency.
Fig. 4.3 is a diagram that will assist us in unpacking these components. In it we analyze the motion of heating as seen in the heating of water from 0o to 100o C. Note that there are two beakers in the figure, one standing alone on a table, the other on a Bunsen burner with a flame under it. Let us assume that, at the moment illustrated, there is a thermometer in each beaker and that both read 30o . In the case of the water standing in the beaker at 30o and, say, in an ambient medium that is also at 30o, the first two elements of the definition have been verified. When at 0o the water was in potency to being at 30o, and that potency has now been actualized, so we can say that the water heated to 30o is an example of (1) the actualizing (2) of what exists in potency.
Now contrast this with the case of the water being heated on the Bunsen burner. At the moment shown, the water temperature as measured by the thermometer reads 30o, indicating not that the water is standing at 30o but rather that it is "transiently" at that temperature, that it is "passing through" 30o. Obviously in this case the first two elements of the definition of motion are verified, for this also is (1) the actualizing (2) of what exists in potency. But here something more is going on. In the case of water actually heating, the water not only has been heated to 30o, but in the very attainment of the 30th degree it is already on its way to a higher degree, that is, to further actualization. That is the sense of the third element, (3) precisely as it is still in potency to further actualizing. In the second case the actualizing at 30o is an imperfect actualizing, and the on-going actualizing of its continuing potency (which is its "passing through" that degree) is what is meant by motion. In this case, that is what is meant by the water heating.
Perhaps, in thinking about this, you wonder why we do not put into the definition of heating such expressions as that the water is "transiently" at 30o, or is "passing through" 30o? The reason is simple. To do so would in effect be using a synonym for motion to define motion. Being "transiently at 30o" or "in transit through 30o" or "passing through 30" is just another way of saying that the water is heating, and so the definition would be circular. Aristotle would overcome this difficulty by focusing on the "in potency" in the definition and using it twice (or reduplicatively). "Motion is the actualizing of what exists in potency precisely as it is in potency." This uses only act and potency and still can capture the essence of motion. Aristotle admitted that this definition is difficult to grasp, but it is not circular and, he went on to say, it is not incapable of existing.
The example of heating is a change of quality, a motion that is referred to as alteration. The other two types of motion to be considered are change of location, which is referred to as local motion, and change of quantity, which is referred to as augmentation if the quantity increases and diminution if the quantity decreases.
Let us repeat our analysis for the case of local motion, which is the easiest to understand and provides the paradigm for the other two types of motion. Suppose that a bird is flying through the air from a tree to a church steeple. When is the bird flying? It is flying when it has left the tree and has not yet arrived at the church. Flying then is covering a distance when part of the distance has been traversed and more of the distance remains to be traversed. In this sense it is the actualizing of the potency to be in a different place, while still in potency to a yet more distant place. Suppose that in flying to the church from the tree the bird alights on a telephone pole. As soon as it alights on the pole it has stopped flying and that motion has been completed. Then the case is similar to that of the water standing at 30o. If the bird takes off again and continues on to the church steeple, it is flying again, but now with another motion.
Earlier we mentioned that plants and animals both have a developmental power which is the cause of growth within the organism. This is not growth by accretion, the pasting on of new parts from outside the plant or animal. It is growth from within, by a process of metabolism and nutrition, as we have tried to explain. When, then, is an organism growing, or undergoing augmentation? When it has already grown but has still more to grow. The case is exactly the same as the water heating and the bird flying. The plant or animal is growing when it has grown and will be growing -- precisely at the point in between what has already occurred and what has yet to occur.
Now let us return to the case of the water heating over the Bunsen burner, for here it is a simple matter to identify the agent that is causing the heating, namely, the flame under the water. We already have a general idea of what causes the bird to fly and the plant to grow, namely, the motive power within the bird and the developmental power within the plant. With the bird and the plant we are dealing with immanent actions in the sense that its motion and its cause are in the same substance. But in the case of the water heating, we are dealing with a transient action and with different substances, the fire and the water, and this presents an interesting problem. It enables us to learn something more about motion, and also to get a better insight into efficient causality.
The question here basically concerns the subject of motion. We know what motion is, and we may wonder where the motion is. To put the question more precisely, is the heating in the water, or in the flame, or is it in both? The answer to that question leads us to the first a priori demonstration in the science of nature. It will be a priori because it will follow from the definition of motion we have already established, and it will actually provide us with a second definition of motion. The demonstration will show that the heating is properly in the water, that is, that the proper subject of motion is the thing moved, the moveable, in this case, the thing heated or the heatable, the water being heated.
Fig. 4.4 presents the demonstration in syllogistic form, which reads as follows:
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The actualizing of what is in potency |
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But motion is the actualizing |
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Therefore, motion is |
The first sentence here, called the major premise, merely restates the result of the reasoning process we have just gone through. What we are talking about is an actualizing of a potency that is going on. What potency are we focusing on? It is the potency of a subject that is capable of being moved or changed. The subject here is the water being heated. That is precisely what we have been talking about.
Now look at the second sentence, called the minor premise. This is the first definition of motion, which we have already established.
When we put the two together, we get the conclusion immediately: Motion is the actualizing of the moveable (changeable) insofar as it is moveable (changeable). Reflecting on this we can see that we have here another definition of motion, which is referred to as its second definition. The first definition, expressed in the minor premise, describes motion in terms of its proper formality, or in terms of its formal cause. The new definition describes motion in terms of its proper subject, its proper matter, and so in terms of its material cause.
The middle term of the syllogism here is a formal cause, and it concludes to a formal effect, namely, the proper subject in which motion is found. Hence the demonstration, going from cause to effect, is a priori, as we explained in our first lecture.
Let us now illustrate the second definition of motion in terms of the examples we have already given of the first definition.
In the case of heating, which is an alteration, "motion is the actualizing of the potential insofar as it is potential" now translates into "heating is the actualizing of the heatable insofar as it is heatable." The heatable here is the water being heated by the flame. Where is the heating? It is in the water.
In the case of flying, which is a local motion, "motion is the actualizing of the potential insofar as it is potential" translates into "flying is the actualizing of the bird's ability to be in a place other than where it now is." In other words, flying is in the bird, the subject that is successively in the different places that are traversed.
In the case of growing, which is an augmentation, "motion is the actualizing of the potential insofar as it is potential" translates into "growing is actualizing of the plant's ability to be of a size larger than it now is." In other words, growth is in the plant, the subject that is successively undergoing increases in its dimensive quantity.
Admittedly it is easier to see that flying is in the bird and that growing is in the plant than it is to see that heating is in the water. The reason for this is that the flying and the growing are activities of living things and thus they involve elements of immanent activity, that is, activity that in some way remains within the agent that is causing it. The heating of the water is different in the sense that the heating passes out of the flame and into the water. In other words, it is an instance of transient action. In such an action it seems that there is a sense in which heating can be attributed to the flame. After all, it is the flame that heats the water, so why is not heating also in some way in the flame?
It was consideration of difficulties such as this that led Aristotle to augment the number of categories beyond those we have already been treating. Thus far, of the ten categories, we have looked at four: the categories of substance, quantity, quality, and location in place. Now there are two more among those we enumerated earlier that attract our attention. These are the categories of action and reception. We need these precisely to address the problem we have now raised.
Fig. 4.5, in its upper portion, shows a simple schematic diagram of the flame heating the water. The flame is shown as a circle and the water as a box. The two are touching, to indicate that the flame is in contact with the water. There is an arrow in the box that starts at the point of contact and otherwise traverses the box. This arrow represents motion, in this case the heating. Notice that it is in the water, because it is the water that is being heated. But the heating involves two things, the flame and the water. The flame is the agent or the physical cause of the heating, and its operation is called action. The water is the recipient of the agent's action, and its receiving is called reception. In Latin "reception" is termed passio, and this terminology passes over into English, so that reception is frequently called passion. Thus we have the couplet "action and passion," which means the same thing as "action and reception."
From the diagram it appears obvious that the action and the reception are both intimately related to the motion. In fact, they are really the same thing as the motion. Action is motion as it is from the agent, and reception is motion as it is in the recipient. Consider now, in the lower portion of Fig. 4.5, the arrow we are using to represent the motion. The left part of the arrow, that beginning with the point of contact where the circle and the box intersect and extending forward, can be seen as representing the action. The right part of the arrow, that starting with the arrowhead and extending backward, can be seen as representing the reception. Both are identified with the motion, but as seen from different directions.
Consider now the question: are the left part of the line and the right part of the line really different from the line itself? Clearly, there is a real distinction between the left part of the line and the right part of the line. The one is not the other. And, in a sense, the two parts of the line are also different from the line in its entirety. But they are different in a minimal sense that depends on the mind's way of considering things. This type of difference is known as a distinction of reason. Action and reception are really different from each other, but they are different from motion merely by a distinction of reason.
Now a further question arises. We have seen that motion is in the moveable, that is, it is in the recipient of the action. But where is action and where is reception? With regard to the second, reception, there is no problem. Obviously it is in the same place as the motion, and so it is in the recipient.
With regard to the action, however, the answer is not as simple. Is there an actualizing in the agent that corresponds to the agent's activity? Surely there is in the case of the flame, if the flame is heating the water. But now take the Bunsen burner out from under the beaker of water and put it to one side with the flame still burning. Is the flame now burning by itself still an agent, if it is not heating the water? One can make a distinction here. There is a sense in which the flame can be regarded as a heating agent even when it is not heating. This is in the sense that the flame is able to heat, or has the power to heat, even though it is not heating. We can refer to this as the flame being an agent in first act, that is, as having the potential to heat. But it is only when the flame is in contact with the water, and heating the water, that we can say it is truly an efficient cause. We say then that it is an agent in second act, that is, that it is a cause actually causing. For it is only then that the flame is really heating the water and so is the efficient cause of the water's being heated.
All of this discussion, it turns out, is relevant to answering the question, "where is action?" It seems to be in the agent when the agent is in second act. But the action will already have had to be transferred to the recipient if the causing is actually taking place. Therefore there is a strong case for the action being also in the recipient when the agent is in second act. This twofold solution is usually accounted for by saying that predicamental or transitive action exists in two places. It exists inchoatively or in incipient fashion in the agent, but it exists terminatively or in completed fashion only when it is in the recipient. It is only then that the flame is a cause actually causing the water's being heated.
Action and reception do not constitute separate types of motion, for they are really identified with motion. As we have said, action is motion considered as being from the agent, whereas reception is the same motion considered as in the recipient. It is noteworthy that none of the remaining categories of being -- relation, time, situation, and vestition -- give rise to additional types of motion. It is true that changes occur in these categories, but none do so directly. They always occur through a prior change in one of the three types of motion we have already discussed, namely, those in the categories of location, quality, and quantity. It is changes in these that indirectly give rise to changes in the category of relation, time, situation, and so on.
From what we have said thus far, it should be clear that motion or change, in the sense we have been considering it, is sensible and successive movement. That is, it is perceptible by the senses, and it does not take place instantaneously but does so over a period of time. Another way of stating this is to say that sensible motion always traverses a "distance" of some sort. This is most clearly seen in the examples we have already analyzed of the bird's flying and the plant's growing. When the bird flies from "here" to "there" it obviously traverses the distance between the two places, for example, that between the tree top and the church steeple. And when the plant grows from "small" to "large" there is a change in its quantitative dimensions. The plant always has some size, but the size changes as it grows. The interval between small and large, in its case, is similar to the interval between here and there, and in this sense we can say that the plant also traverses a "distance" as it continues to grow.
The heating of the water is slightly different. In the other two cases it is easy to see that the distance can be quantified. There is a distance of length in the flight of the bird, and there is a distance of quantitative dimensions in the growth of the plant. The heating of water can be quantified also, but this has to be done through a process of measurement. The water's heating can be measured through the use of a thermometer, which measures the degree of heat within the water at any one moment. This gives a quantitative measure of heating, since through the process of measurement the heating comes to be seen as the traversal of various degrees of heat from 0o to 100o. Earlier in this lecture we have used this "distance," and its traversal, to explain the first definition of motion given by Aristotle. Analogous measures of other changes in quality are also available. Through their use all alterations of sensible qualities can also be seen as traversing a quantitative length -- what we have been calling a "distance."
We may refer to the three types of motion -- local motion, growth, and alteration -- as motion's qualitative parts. Apart from these "parts," motion has also quantitative parts by reason of this distance that it traverses. These quantitative parts are best seen in local motion, where the magnitude the motion traverses, otherwise known as extension, manifests all the properties of a continuum. Since in the other types of motion the change is in some way sensible, we may say that all motion traverses the sensible continuum. Thus motion is, by its very nature, continuous.
But the continuum that is motion is not the same as a static continuum such as a line, all of whose parts co-exist and are known at the same time. Rather motion is a flowing continuum. Like the line, it has parts, but these parts come into existence only successively. We know the parts of a motion only because we are able to retain them in memory. We shall explain this peculiar aspect of motion in greater detail in our next lecture, after we have treated the subject of time.
Fig. 4.1 A Powers Model of a Plant Nature
Fig. 4.2 A Powers Model of an Animal Nature
Fig. 4.4 The Proper Subject of Motion