Word
Gems
What is a
man but the sum of his thoughts?
- Mortimer Adler's
- Syntopicon
Essays
Change
FROM the pre-Socratic physicists and the ancient philosophers to Darwin, Marx, and
James--and, in our own 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
Zeno's paradoxes seem to do, according to one interpretation of them. But if argument
cannot refute the testimony of the senses, neither can reasoning 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
things and to change itself--these are questions to which answers are not obtainable
merely by observation. Nor will simple observation, without the and of experiment,
measurement, and mathematical calculation, discover the laws and properties of motion.
The analysis of change or motion has been a problem for the philosophers of nature. They
have been concerned with the definition of change, its relation to being, the
classification of the kinds of change. The measurement of motion, on the other hand, and
the mathematical formulation of its laws have occupied the experimental natural
scientists. Both natural philosophy and natural science share a common subject matter,
though they approach it by different methods and with different interests. Both are
entitled to use the name "physics" for their subject matter.
The Greek word phusis from which "physics" comes has, as its Latin
equivalent, the word natura from which "nature" comes. In their
original significance, both words had reference to the sensible world of changing things,
or to its underlying principle--to the ultimate source of change. The physics of the
philosopher and the physics of the empirical scientist are alike inquiries concerning the
nature of things, not in every respect but in regard to their change and motion. The
conclusions of both inquiries have metaphysical implications for the nature of the
physical world and for the character of physical existence.
The philosopher draws these implications for being from the study of becoming. The
scientist, in turn, draws upon philosophical distinctions in order to define the objects
of his study. Galileo, for example, in separating the problem of freely falling bodies
from the motion of projectiles, employs the traditional philosophical distinction between
natural and violent motion. The analysis of time and space (basic variables in Newtonian
mechanics), the distinction between discontinuous and continuous change, and the problem
of the divisibility of a continuous motion--these are philosophical considerations
pre-supposed by the scientific measurement of motion.
WE HAVE so far used the words "change" and "motion," as well as
"becoming," as if all three were interchangeable in meaning. That is somewhat
inaccurate, even for the ancients who regarded all kinds of change except one as motions;
it is much less accurate for the moderns who have tended to restrict the meaning of
"motion" to local motion or change of place. It is necessary, therefore, to
examine briefly the kinds of change and to indicate the problems which arise with these
distinctions.
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 'accident' in any sense of the term), it is 'coming to be,' and the
converse change is 'passing away."' Aristotle also uses other pairs of words --
"generation" and "corruption," "becoming" and
"perishing" -- to name the last kind of change.
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 Aristotle's 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 the 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. Aristotle's
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 the
three things 'wood,' 'hot,' and 'cold,' of which the first is that which is in motion, the
second is that which 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 in the increase or
decrease which occurs with a body's change in quantity and in the local motion which
occurs with a body's change of place, that which changes persists throughout the change as
the same kind of substance. The wood does not cease to be 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."
Because the substance of the changing thing remains the same while changing in its
properties-i.e., in such attributes or accidents as quality, quantity, and place-Aristotle
groups the three kinds of motion together as accidental change. The changing thing does
not come to be or pass away absolutely, but only in a certain respect. In contrast,
generation and corruption involve a change in the very substance of a thing. "When
nothing perceptible persists in its identity as a substratum, and the thing changes as a
whole," then, according to Aristotle, "it is a coming-to-be of one substance,
and the passing-away of another."
In such becoming or perishing, it is matter itself rather than a body or a substance which
is transformed. Matter takes on or loses the form of a certain kind of substance. For
example, when the nutriment is assimilated to the form of a living body, the bread or corn
becomes the flesh and blood of a man. When an animal dies, its body decomposes into the
elements of inorganic matter. Because it is a change of substance itself, Aristotle calls
the one kind of change which is not motion substantial change, and speaks of it
as "a coming-to-be or passing-away simply" -- that is, not in a certain respect,
but absolutely or "without qualification."
These distinctions are involved in a long tradition of discussion and controversy. They
cannot be affirmed or denied without opposite sides being taken on the fundamental issues
concerning substance and accident, matter and form, and the causes of change or motion.
The adoption or rejection of these distinctions affects one's view of the difference
between inorganic and organic change, and the difference between the motions of matter and
the changes which take place in mind. The statement of certain problems is determined
accordingly; as, for example, the problem of the transmutation of the elements, which
persists in various forms from the physics of the ancients through mediaeval alchemy and
the beginnings of modern chemistry to present considerations of radioactivity and atomic
fission.
SINCE THE 17TH CENTURY, motion has been identified with local motion. "I can conceive
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 kinds 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 forces
by which the particles of bodies, by some causes hitherto unknown, are either mutually
impelled towards one another, and cohere in regular figures, 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 we call locomotion, that must be primary."
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 transference 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 the 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 Aristotle's 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
complete 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 become 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 those 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, that it was actus entis in
potentia quatenus in potentia; I ask whether any one can imagine he could thereby
have guessed what the word beweeginge signified?"
Locke does not seem to be satisfied with any definition of motion. "The atomists, who
define motion to be 'a passage from one place to another,' what do they more than put one
synonymous word for another? For what is passage other than motion?. . . Nor will 'the
successive application of the superficies of one body to those of another,' 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 the deepest significance. It occurs not only in Descartes' 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 the 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 its 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 movent is no longer in contact with them?" 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 the motion. For the potentiality to be progressively reduced to
actuality, it must be continuously acted upon.
Aristotle's answer postulates a series of causes so that contact can be maintained between
the projectile and the moving cause. "The original movent," he writes,
"gives the power of being a movent 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 movent 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 quantity of the impressed force which originally set it in
motion.
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 Plato's 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 the 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 the 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.
Neither of the contrary forms changes. Only the thing composite of matter and form changes
with respect to the forms of its matter. Hence these principles of change are themselves
unchanging. Change takes place through, not in, them. As constituents of the changing
thing, they are the principles of its mutable being, principles of its being as well as of
its being mutable.
The explanation of change by reference to what does not change seems to be common to all
theories of becoming. Lucretius, as we have already seen, explains the coming to be and
passing away of all other things by the motions of atoms which neither come to be nor pass
away. The eternity of the atoms underlies the mutability of everything else.
Yet the atoms are not completely immutable. They move forever through the void which,
according to Lucretius, is required for their motion. Their local motion is, moreover, an
actual property of the atoms. For them, to be is to be in motion. Here then, as in the
Cartesian theory, no potentiality is involved, and motion is completely real and
completely intelligible.
THE NOTIONS of time and eternity are inseparable from the theory of change or motion. As
the chapters on TIME and SPACE indicate, local motion involves the dimensions of space as
well as time, but all change requires time, and time itself is inconceivable apart from
change or motion. Furthermore, as appears in the chapters on TIME and ETERNITY, the two
fundamentally opposed meanings of eternity differ according to whether they imply endless
change or absolute changelessness.
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 immutable being. The eternal in this sense, as
Montaigne points out, is not merely that "which never had beginning nor never shall
have ending," but rather that "to which time can bring no mutation."
There 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 motion 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 always have 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."
Aristotle's 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 an unceasing motion, which is motion in a circle." He calls this motion of the
first heavenly sphere "the simple spatial movement 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 substances. 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 world's 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 of the forms of motion.
THE PHILOSOPHICAL and theological issues concerning creation and change, eternity and
time, are further discussed in the chapters on CAUSE, ETERNITY, and WORLD. Other problems
arising from the analysis of change must at least be briefly mentioned here.
Though less radical than the difference between creation and change, the difference
between the motions of inert or non-living things and the vital activities of plants and
animals raises for any theory of change the question whether the same principles apply to
both. The rolling stone and the running animal both move locally, but are both motions
locomotion in the same sense? Augmentation occurs both in the growth of a crystal and the
growth of a plant, but are both of them growing in the same sense? In addition, there
seems to be one kind of change in living things which has no parallel in the movements of
inert bodies. Animals and men learn. They acquire knowledge, form habits and change them.
Can change of mind be explained in the same terms as change in matter?
The issues raised by questions of this sort are more fully discussed in the chapters on
ANIMAL, HABIT, and LIFE. Certain other issues must be entirely reserved for discussion
elsewhere. The special problems of local motion--such as the properties of rectilinear and
circular motion, the distinction between uniform and variable motion, and the uniform or
variable acceleration of the latter--are problems which belong to the chapters on
ASTRONOMY and MECHANICS. Change, furthermore, is a basic fact not only for the natural
scientist, but for the historian--the natural historian or the historian of man and
society. The considerations relevant to this aspect of change receive treatment in the
chapters on EVOLUTION, HISTORY, and PROGRESS.
Even these ramifications of discussion do not exhaust the significance of change. The
cyclical course of the emotions and the alternation of pleasure and pain have been thought
inexplicable without reference to change of state in regard to desire and aversion--the
motion from want to satisfaction, or from possession to deprivation. Change is not only a
factor in the analysis of emotion, but it is also itself an object of man's emotional
attitudes. It is both loved and hated, sought and avoided.
According to Pascal, man tries desperately to avoid a state of rest. He does everything he
can to keep things in flux. "Our nature consists in motion," he writes;
"complete rest is death .... Nothing is so insufferable to man," he continues,
"as to be completely at rest, without passions, without business, without diversion,
without study. He then feels his nothingness, his forlornness, his dependence, his
weakness, his emptiness." Darwin does not think that the desire for change is
peculiar to man. "The lower animals," he writes, "are . . . likewise
capricious in their affections, aversions, and sense of beauty. There is also reason to
suspect that they love novelty for its own sake."
But men also wish to avoid change. The old Prince Bolkonski, in War and Peace,
"could not comprehend how anyone could wish to alter his life or introduce anything
new into it." This is not merely an old man's view. For the most part, it is
permanence rather than transiency, the enduring rather than the novel, which the poets
celebrate when they express man's discontent with his own mutability. The withering and
perishing of all mortal things, the assault of time and change upon all things familiar
and loved, have moved them to elegy over the evanescent and the ephemeral.
- From Virgil's Sunt lacrimae rerum et mentem mortalia
tangunt to Shakespeare's "Love is not love which alters when it alteration
finds," the poets have mourned the inevitability of change.
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