Change.

In PART I we will discuss how philosophers have looked at change over history. We will also discuss the four kinds of change and the three kinds of motion.

In PART II we will discuss the primacy of local motion (or locomotion).

In PART III we will contrast the Aristotelian model of change with the Cartesian model of change.

In PART IV we will discuss the unchanging properties of change. We will also discuss Aristotlešs theory of the prime mover.

From the pre-Socratic physicists and the ancient philosophers to Darwin, Marx, and James and, in our day, Dewey and Whitehead the fact of change has been a major focus of speculative and scientific inquiry.

Except by Parmenides and his school, the existence of change has never been denied.

Nor can it be without rejecting all sense-perception as illusory, which is precisely what Zenošs paradoxes seem to do, according to one interpretation of them.

But if argument cannot refute the testimony of the senses, neither can reason support it.

The fact of change, because it is evident to the senses, does not need proof.

-That change is, is evident, but -what change is is neither evident nor easy to define.

What principles or factors are common to every sort of change, how change or becoming is related to permanence or being, what sort of existence belongs to mutable beings and to change itself these are questions to which answers are obtainable merely by observation.

Nor will simple observation, without the aid of experiment, measurement, and mathematical calculation, discover the laws and properties of motion.

In his physical treatises, Aristotle distinguishes four kinds of change.

"When the change from contrary to contrary is -in quantity ," he writes, "it is growth and diminution ;"

"when it is -in place , it is motion ;"

"when it is . . . -in quality it is alteration ;"

"but when nothing persists of which the resultant is a property (or an accidentš in any sense of the term), it is coming to be and the converse change is passing away ."

Of the four kinds of change, only the last is not called "motion."

But in the context of saying that "becoming cannot be a motion," Aristotle also remarks that "every motion is a kind of change."

He does not restrict the meaning of motion to change in place, which is usually called "local motion" or "locomotion."

There are, then, according to Aristotlešs vocabulary, three kinds of motion:

(1) local motion in which bodies change from place to place.

(2) alteration or qualitative motion , in which bodies change with respect to such attributes as color, texture, or temperature.

(3) increase and decrease, or quantitative motion , in which bodies change in size.

And, in addition, there is the one kind of change which is not motion generation and corruption.

This consists in the coming to be or passing away of a body which, while it has being, exists as an individual substance of a certain sort.

Becoming and perishing are most readily exemplified by the birth and death of living things, but Aristotle also includes the transformation of water into ice or vapor as examples of generation and corruption.

One distinctive characteristic of generation and corruption, in Aristotle's conception of this type of change is their instantaneity.

He thinks that the other three kinds of change are continuous processes, taking time, whereas things come into being or pass away instantaneously.

Aristotle thus applies the word "motion" only to the continuous changes which time can measure.

He never says that time is a measure of change, but only of motion.

But the contrast between the one mode of change which is not motion and the three kinds of motion involves more than this difference with regard to time and continuity.

Aristotlešs analysis considers the subject of change that which undergoes transformation and the starting-point and goal of motion.

"Every motion," he says, "proceeds from something and to something, that which is directly in motion being distinct from that to which it is in motion and that from which it is in motion;"

"for instance, we may take three things, wood, hot, and cold, of which the first is that which is in motion, the second is that to which the motion proceeds, and the third is that from which it proceeds."

In the alteration which occurs when the wood changes quality, just as the increase or decrease which occurs with a bodyšs change in quality and in the local motion which occurs with a bodyšs change in place, -that which changes persists throughout the change as the same kind of substance.

The wood does not cease to become wood when it becomes hot or cold;

the stone does not cease to be a stone when it rolls from here to there, or the organism an animal of a certain kind when it grows in size.

In all these cases, "the substratum"that which is the subject of change"persists and changes in its own properties . . . The body, although persisting as the same body, is now healthy and now ill;"

"and the bronze is now spherical and at another time angular, and yet remains the same bronze."

In PART II we will discuss the primacy of local motion (or locomotion).

Since the 17th century, motion has been identified with local motion.

"I can conceive of no other kind" of motion, Descartes writes, "and do not consider that we ought to conceive any other in nature."

As it is expressed "in common parlance," motion, he says, " is nothing more than the -action by which any body passes from one place to another ."

This can hardly be taken to mean that change of place is the only observable type of change.

That other types of change are observable cannot be denied.

The science of mechanics or dynamics may be primarily or exclusively concerned with local motions, but other branches of natural science, certainly chemistry, deal with qualitative transformations;

And the biological sciences study growth and decay, birth and death.

The emphasis on local motion as the only kind of motion, while it does not exclude apparent changes of other sorts, does raise a question about their reality.

The question can be put in several ways.

Are the various -apparently different kinds of change really distinct, or can they all be reduced to aspects of one underlying mode of change which is local motion?

Even supposing that the kinds of change are not reducible to one another, is local motion primary in the sense that it is involved in all the others?

When mechanics dominates the physical sciences (as has been so largely the case in modern times), there is a tendency to reduce all the observable diversity of change to various appearances of local motion.

Newton, for example, explicitly expresses this desire to formulate all natural phenomena in terms of the mechanics of moving particles.

In the Preface to the first edition of his -Mathematical Principles , after recounting his success in dealing with celestial phenomena, he says: "I wish we could derive the rest of the phenomena of Nature by the same kind of reasoning from mechanical principles, for I

am induced by many reasons to suspect that they may all depend upon certain principles by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled towards one another, and cohere in regular features, or are repelled and recede from one another."

The notion that all change can be reduced to the results of local motion is not, however of modern origin.

Lucretius expounds the theory of the Greek atomists that all the phenomena of change can be explained by reference to the local motion of indivisible particles coming together and separating.

Change of place is the only change which occurs on the level of the ultimate physical reality.

The atoms neither come to be nor pass away, nor change in quality or size.

But though we find the notion in ancient atomism, it is only in modern physics that the emphasis upon local motion tends to exclude all other kinds of change.

It is characteristic of what James calls "the modern mechanico-physical philosophy" to begin "by saying that the -only facts are collocations and motions of primordial solids, and the only laws the changes of motion which changes in collocation bring."

James quotes Helmholtz to the effect that "the ultimate goal of theoretic physics is to find the last -unchanging causes of the processes of Nature."

If, to this end, "we imagine the world composed of elements with unalterable qualities," then, Helmholtz continues, "the only changes that can remain in such a world are spatial changes, i.e. movements, and the only outer relations which can modify the action of the

forces are spatial too, or, in other words, the forces are motor forces dependent for their effect on spatial relations."

In the history of physics, Aristotle represents the opposite view.

No one of the four kinds of change which he distinguishes has for him greater physical reality than the others.

Just as quality cannot be reduced to quantity, or either of these to place, so in his judgment the motions associated with these terms are irreducible to one another.

Yet Aristotle does assign to local motion a certain primacy.

"Motion in its most general and primary sense," he writes, "is change of place, which we call locomotion."

He does not mean merely that this is the primary sense of the word, but rather that no other kind of motion can occur without local motion being somehow involved in the process.

Showing how increase and decrease depends on alteration, and how that in turn depends on change of place, he says that "of the three kinds of motion . . . it is this last which se call locomotion, that must be primary.

In PART III we will contrast the Aristotelian model of change with the Cartesian model of change.

The shift in meaning of the word "motion" would not by itself mark a radical departure in the theory of change, but it is accompanied by a shift in thought which has the most radical consequences.

At the same time that motion is identified with local motion, Descartes conceives motion as something completely actual and thoroughly intelligible.

For the ancients, becoming of any sort had both less reality and less intelligibility than being.

Aristotle had defined motion as the actuality of that which is potential in a respect in which it is still potential to some degree.

According to what Descartes calls its strict as opposed to its popular meaning, motion is "the transferrence of one part of matter or one body from the vicinity of those bodies that are in immediate contact with it, and which we regard as in repose, into the vicinity of others."

This definition‹contrasted with the Aristotelian conception which it generally supersedes in the subsequent tradition of natural science‹is as revolutionary as the Cartesian analytical geometry is by comparison with the Euclidean.

Nor is it an unconnected fact that the analytical geometry prepares the way for differential calculus that is needed to measure variable motions, their velocities, and their accelerations.

The central point on which the two definitions are opposed constitutes one of the most fundamental issues in the philosophy of nature.

Does motion involve a transition from potential to actual existence, or only the substitution of one actual state for another‹only a "transportation," as Descartes says, from one place to another?

While motion is going on, the moving thing, according to Aristotlešs definition, must be partly potential and partly actual in the same respect.

The leaf turning red, -while it is altering , has not yet fully reddened.

When it becomes as red as it can get, it can no longer change in that respect.

Before it began to change, it was actually green, and since it could become red, it was potentially red.

But while the change is in process, the potentiality of the leaf to become red is being actualized.

This actualization progresses until the change is completed.

The same analysis would apply to a ball in motion.

Until it comes to rest in a given place, its potentiality for being there is undergoing progressive actualization.

In short, motion involves some departure from pure potentiality in a given respect, and never attainment of full actuality in that same respect.

When there is no departure from potentiality, motion has not yet begun; when the attainment of actuality is complete, the motion has terminated.

The Aristotelian definition of motion is the object of much ridicule in the 17th century.

Repeating the phrasing which had been traditional in the schools‹ the actualization of what exists in potentiality, in so far as it is potential."

Descartes asks: "Now who understands these words? And who at the same time does not know what motion is? Will not everyone admit that these philosophers have been trying to find a knot in a bulrush?"

Locke also finds it meaningless:

"What more exquisite jargon could the wit of man invent than this definition . . . which would puzzle any rational man to whom it was not already known by its famous absurdity, to guess what word it could ever be supposed to be the explication of."

"If Tully, asking a Dutchman what -beweeginge was," Locke continues, "should have received this explication in his own language was actus entis in potentia quatenus in potentia; I ask whether any one can imaging he could thereby have guessed what the word -beweeginge signified?"

Locke does not seem to be satisfied with any defintion of motion.

"The atomists, who define motion to be Œach passage from one place to anotherš what do they more than put one synonymous word for another? For what is -passage other than -motion ? . . . Nor will Œthe successive application of the superficies of one body to those of another,š which the Cartesians give us, prove a much better definition of motion, when well examined."

But though Locke rejects the definition of the atomists and the Cartesians on formal grounds, he accepts their idea of motion as simply change of place; whereas he dismisses the Aristotelian definition as sheer absurdity and rejects the idea that motion or change necessarily involves a potentiality capable of progressive fulfillment.

As we have already remarked, the omission of potentiality from the conception of motion is a theoretical shift of deepest significance.

It occurs not only in Descartesš -Principles of Philosophy and in the atomism of Hobbes and Gassendi, but also in the mechanics of Galileo and Newton.

According to these modern philosophers and scientists, a moving body is -always actually somewhere.

It occupies a different place at every moment in a continuous motion.

The motion can be described as the successive occupation by the body of different places at different times.

Though all the parts of the motion do not coexist, the moving particle is completely actual throughout.

It loses no reality and gains none in the course of motion, since the various positions the body occupies lie totally outside its material nature.

It would, of course, be more difficult to analyze alteration in color or biological growth in these terms, but it must be remembered that efforts have been made to apply such an analysis through the reduction of all other modes of change to local motion.

The principle of inertia, first discerned by Galileo, is critically relevant to the issue between these two conceptions of motion.

It is stated by Newton as the first of his "axioms or laws of motion."

"Every body," he writes, "continues in a state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it."

As applied to the motion of projectiles, the law declares that they "continue in their motions, so far as they are not retarded by the resistance of air, or impelled downwards by the force of gravity."

In his experimental reasoning concerning the acceleration of bodies moving down inclined planes, Galileo argues that a body which has achieved a certain velocity on the descent would, if it then proceeded along a horizontal plane, continue infinitely at the same velocity‹except for the retardation of air resistance and friction.

"Any velocity once imparted to a moving body" he maintains, "will be rigidly maintained as long as the external causes of acceleration or retardation are removed."

So in the case of projectiles, they would retain the velocity and direction imparted to them by the cannon, were it not for the factors of gravity and air resistance.

Bodies actually in motion possess their motion in themselves as a complete actuality.

They need no causes acting on them to keep them in motion, but only to change their direction or bring them to rest.

The motion of projectiles presents a difficulty for the theory which describes all motion as a reduction of potency to act.

"If everything that is in motion, with the exception of things that move themselves, is moved by something else, how is it," Aristotle asks, "that some things, e.g., things thrown, continue to be in motion when their movement is no longer in contact with

This is a problem for Aristotle precisely because he supposes that the moving cause must act on the thing being moved throughout the period of motion.

For the potentiality to be progressively reduced to actuality, it must be continuously acted

Aristotlešs answer postulates a series of causes so that contact can be maintained between the projectile and the moving cause.

"The original movement," he writes, "gives the power of being a movement either to air or to water or to something else of the kind, naturally adapted for imparting and undergoing motion . . . The motion begins to cease when the motive force produced in

one member of the consecutive series is at each stage less than that possessed by the preceding member, and it finally ceases when one member no longer causes the next member to be a movement but only causes it to be in motion."

It follows that inertia must be denied by those who hold that a moving body -always requires a mover; or even that a body cannot sustain itself in motion beyond a point proportionate to the quality of the impressed force which originally set it in motion.

It follows that inertia must be denied by those who hold that a moving body -always requires a mover; or even that a body cannot sustain itself in motion beyond a point proportionate to the quality of the impressed force which originally set it in motion.

In PART IV we will discuss the unchanging properties of change. We will also discuss Aristotlešs theory of the prime mover.

For the ancients, the basic contrast between being and becoming (or between the permanent and the changing) is a contrast between the intelligible and the sensible.

This is most sharply expressed in Platošs distinction between the sensible realm of material things and the intelligible realm of ideas.

"What is that which always is and has no becoming," Timaeus asks; "and what is that which is always becoming and never is?"

He answers his own question by saying that "that which is apprehended by intelligence and reason is always in the same state; but that which is conceived by opinion with the help of sensations and without reason, is always in a process of becoming and perishing, and never really is."

Even though Aristotle differs from Plato in thinking that change and changing can be objects of scientific knowledge, he too, holds becoming to be less intelligible than being, precisely because change necessarily involves potentiality.

Yet becoming can be understood to the extent that we can discover the principles of its being‹the unchanging principles of change.

"In pursuing the truth," Aristotle remarks‹and this applies to the truth about change as well as everything else‹"one must start from the things that are always in the same state and suffer no change."

For Aristotle, change is intelligible through the three elements of permanence which are its principles: (1) the enduring substratum of change, and its contraries‹(2) that to which, and (3) that from which, the change takes place.

The same principles are sometimes stated to be (1) matter, (2) form, and (3) privation; the matter or substratum being that which both lacks a certain form and has a definite potentiality for possessing it.

Change occurs when the matter undergoes a transformation in which it comes to have the form of which it was deprived by the possession of a contrary form.

The notions of time and eternity are inseparable from theory of change or motion.

Eternity is sometimes identified with infinite time.

It is in this sense that Plato, in the -Timaeus , refers to time as "the moving image of eternity" and implies that time which belongs to the realm of ever-changing things, resembles the eternal only through its perpetual endurance.

The other sense of the eternal is also implied‹the sense in which eternity belongs to the realm of an immutable being.

The eternal in this sense, as Montaigne points out, is not merely that "which never had beginning nor never ahall have ending," but rather that "to which time can bring no mutation."

These are two great problems which use the word "eternity" in these opposite senses.

One is the problem of the eternity of motion: the question whether notion has or can have either a beginning or an end.

The other is the problem of the existence of eternal objects‹immutable things which have their being apart from time and change.

The two problems are connected in ancient thought.

Aristotle, for example, argues that "it is impossible that movement should either have come into being or cease to be, for it must have always existed.

Since "nothing is moved at random, but there must always be something present to move it," a cause is required to sustain the endless motions of nature.

This cause, which Aristotle calls "the prime mover," must be "something which moves without being moved, being eternal, substance, and actuality."

Aristotlešs theory of a prime mover sets up a hierarchy of causes to account for the different kinds of motion observable in the universe.

The perfect circular motion of the heavens serves to mediate between the prime mover which is totally unmoved and the less regular cycles of terrestrial change.

The "constant cycle" of movement in the stars differs from the irregular cycle of "generation and destruction" on earth.

For the first, Aristotle asserts the necessity of "something which is always moved with unceasing motion, which is motion in a circle."

He calls this motion of the first heavenly sphere "the simple spatial motion of the universe" as a whole.

Besides this "there are other spatial movements‹those of the planets‹which are eternal" but are "always acting in different ways" and so are able to account for the other cycle in nature‹the irregular cycle of generation and corruption.

In addition, a kind of changelessness is attributed to all the celestial bodies which Aristotle calls "eternal."

Eternally in motion, they are also eternally in being.

Though not immovable, they are supposed to be incorruptible substance.

They never begin to be and never perish.

The theory of a world eternally in motion is challenged by Jewish and Christian theologians who affirm as an article of their religious faith that "in the beginning God created heaven and earth."

The worldšs motions, like its existence, have a beginning in the act of creation.

Creation itself, Aquinas insists, is not change or motion of any sort, "except according to our way of understanding."

"For change means that the same thing should be different now from what it was previously . . . But in creation, by which the whole substance of a thing is produced, the same thing can be taken as different now and before, only according to our way of understanding, so that a thing is understood as first not existing at all, and afterwards as existing."

Since creation is an absolute coming to be from non-being, no pre-existent matter is acted upon as in generation, in artistic production, or in any forms of motion.

Source: Philosophy-irc.org.