ourselves. He includes under the one common name all the processes by
which things come to be what they are or cease to be what they have
been. Thus he distinguishes the following varieties of "motion":
_generation_ (the coming of an individual thing into being), with its
opposite _decay_ or _corruption_ (the passing of a thing out of being),
_alteration_ (change of _quality_ in a thing), _augmentation_ and
_diminution_ (change in the _magnitude_ of a thing), _motion through
space_ (of which latter he recognises two sub-species, rectilinear
_transference_ and _rotation_ in a circular orbit about an axis). It is
this last variety, motion through space, which is the most fundamental
of all, since its occurrence is involved in that of any of the other
types of process mentioned, though Aristotle does not hold the
thorough-going mechanical view that the other processes are only
apparent, and that, as we should put it, qualitative change is a mere
disguise which mechanical motion wears for our senses.
*The Eternity of Motion*.--Certain very important consequences follow
from the conception of efficient causation which we have been
describing. Aristotle has no sympathy with the "evolutionist" views
which had been favoured by some of his predecessors. According to his
theory of organic generation, "it takes a man to beget a man "; where
there is a baby, there must have been a father. Biological kinds
representing real clefts in Nature, the process of the production of a
young generation by an already adult generation must be thought of as
without beginning and without end. There can be no natural "evolution"
of animals of one species from individuals of a different kind. Nor
does it occur to Aristotle to take into account the possibility of
"Creationism," the sudden coming into being of a fully fledged first
generation at a stroke. This possibility is excluded by the doctrine
that the "matter" of a thing must exist beforehand as an indispensable
condition of the production of that thing. Every baby, as we said, must
have had a father, but that father must also have been a baby before he
was a full-grown man. Hence the perpetuation of unchanging species must
be without beginning and without end. And it is implied that all the
various processes, within and without the organism, apart from which its
life could not be kept up, must be equally without beginning and without
end. The "cosmos," or orderly world of natural processes, is strictly
"eternal"; "motion" is everlasting and continuous, or unbroken. Even
the great Christian theologians who built upon Aristotle could not
absolutely break with him on this point. St. Thomas, though obliged to
admit that the world was actually created a few thousand years before
his own time, maintains that this can only be known to be true from
revelation, philosophically it is equably tenable that the world should
have been "created from all eternity." And it is the general doctrine
of scholasticism that the expression "creation" only denotes the
absolute dependence of the world on God for its being. When we say "God
created the world out of nothing," we mean that He did not make it out
of pre-existing matter, that it depends for its being on Him only; the
expression is purely negative in its import.
*God*.--With the doctrine of the eternity of the world and the processes
which make up its life we come close to the culminating theory of
Aristotelian First Philosophy, its doctrine of God, as the eternal,
unchanging source of all change, movement, and process. All motion is a
process within matter by which the forms latent in it are brought into
actual manifestation. And the process only takes place in the presence
of an adequate efficient cause or source of motion. Hence the eternity
of natural processes involves the existence of one or more eternal
sources of motion. For, if we do not admit the existence of an
unoriginated and ever-present source or sources of motion, our only
alternative is to hold that the world-process is due to a series of
sources of motion existing successively. But such a view would leave the
unity and unbroken continuity of the world-process unaccounted for. It
would give us a succession of processes, temporally contiguous, not one
unbroken process. Hence we argue from the continuity of motion to its
dependence on a source or sources which are permanent and present
throughout the whole everlasting world-process. And when we come to the
question whether there is only one such ultimate source of movement for
the whole universe, or several, Aristotle's answer is that the supreme
"Unmoved Mover" is one. One is enough for the purpose, and the law of
parcimony forbids us to assume the superfluous. This then is the
Aristotelian conception of God and God's relation to the world. God is
the one supreme unchanging being to whose presence the world responds
with the whole process of cosmic development, the ultimate educer of the
series of "forms" latent in the "matter" of the world into actual
manifestation. Standing, as He does, outside the whole process which by
His mere presence He initiates in Nature, He is not himself a composite
of "form" and "matter," as the products of development are. He is a pure
individual "form" or "actuality," with no history of gradual development
behind it. Thus He is a purely immaterial being, indispensable to the
world's existence but transcending it and standing outside it. _How_
His presence inspires the world to move Aristotle tries to explain by
the metaphor of appetition. Just as the good I desire and conceive,
without itself "moving" "moves" my appetition, so God moves the universe
by being its good. This directly brings about a uniform unbroken
rotation of the whole universe round its axis (in fact, the alternation
of day and night). And since this rotation is communicated from the
outermost "sphere" of heaven to all the lesser "spheres" between it and
the immovable centre, the effects of God's presence are felt
universally. At the same time, we must note that though God is the
supreme Mover of the Universe, He is not regarded by Aristotle as its
Creator, even in the sense in which creation can be reconciled with the
eternity of the world. For the effect of God's presence is simply to
lead to the development of "form" in an already existing "matter."
Without God there could be no "form" or order in things, not even as
much as is implied in the differentiation of matter into the four
"elements," yet "primary matter" is no less than God a precondition of
all that happens.
It is characteristic of Aristotle that his God is as far from
discharging the functions of a Providence as He is from being a Creator.
His "activity" is not, as Plato had made it, that of the great "Shepherd
of the sheep." As far as the world is concerned, God's only function is
to be there to move its appetition. For the rest, the unbroken activity
of this life is directed wholly inward. Aristotle expressly calls it an
"activity of immobility." More precisely, he tells us, it is activity
of thought, exercised unbrokenly and everlastingly upon the only object
adequate to exercise God's contemplation, Himself. His life is one of
everlasting _self_-contemplation or "thinking of thought itself." Like
all unimpeded exercise of activity, it is attended by pleasure, and as
the activity is continuous, so the pleasure of it is continuous too. At
our best, when we give ourselves up to the pure contemplative activity
of scientific thought or aesthetic appreciation, we enter for a while
into this divine life and share the happiness of God. But that is a
theme for our chapter on the _Ethics_.
It is a far cry from this conception of a God untroubled by care for a
world to which He is only related as the object of its aspiration to the
God who cares even for the fall of the sparrow and of whom it is
written, _Sic Deus dilexit mundum_, but it was the standing task of the
philosophical theologians of the Middle Ages to fuse the two
conceptions. Plato's God, who, if not quite the Creator, is the "Father
and Fashioner" of us all, and keeps providential watch over the world He
has fashioned, would have lent Himself better to their purposes, but
Plato was held by the mediaeval church to have denied the resurrection
of the body. The combination of Aristotle's Theism with the Theism of
early Christianity was effected by exquisitely subtle logical devices,
but even in St. Thomas one cannot help seeing the seams.
Nor can one help seeing in Aristotle's own doctrine the usual want of
coherence between an initial anti-Platonic bias and a final reversion to
the very Platonic positions Aristotle is fond of impugning. We are told
at the outset that the Platonic "separate forms" are empty names, and
that the real individual thing is always a composite of matter and a
form which only exists "in matter." We find in the end that the source
of the whole process by which "matter" becomes imbued with "form" is a
being which is "pure" form and stands outside the whole development
which its presence sets up. And the issue of Aristotle's warning against
"poetic metaphors" is the doctrine that God moves the world by being
"the object of the world's desire."
*CHAPTER IV*
*PHYSICS*
There is no part of Aristotle's system which has been more carefully
thought out than his Physics; at the same time it is almost wholly on
account of his physical doctrines that his long ascendancy over thought
is so much to be regretted. Aristotle's qualifications as a man of
science have been much overrated. In one department, that of descriptive
natural history, he shows himself a master of minute and careful
observation who could obtain unqualified praise from so great a
naturalist as Darwin. But in Astronomy and Physics proper his
inferiority in mathematical thinking and his dislike for mechanical ways
of explaining facts put him at a great disadvantage, as compared with
Plato and Plato's Pythagorean friends. Thus his authority was for
centuries one of the chief influences which prevented the development of
Astronomy on right lines. Plato had himself both taught the mobility of
the earth and denied correctly that the earth is at the centre of the
universe, and the "Copernican" hypothesis in Astronomy probably
originated in the Academy. Aristotle, however, insists on the central
position of the earth, and violently attacks Plato for believing in its
motion. It is equally serious that he insists on treating the so-called
"four elements" as ultimately unanalysable forms of matter, though Plato
had not only observed that so far from being the ABC (_stoicheia_ or
_elementa_, literally, letters of the alphabet) of Nature they do not
deserve to be called even "syllables," but had also definitely put
forward the view that it is the geometrical structure of the
"corpuscles" of body upon which sensible qualities depend. It is on
this doctrine, of course, that all mathematical physics rests.
Aristotle reverts to the older theory that the differences between one
"element" and another are qualitative differences of a sensible kind.
Even in the biological sciences Aristotle shows an unfortunate proneness
to disregard established fact when it conflicts with the theories for
which he has a personal liking. Thus, though the importance of the
brain as the central organ of the sensori-motor system had been
discovered in the late sixth or early fifth century by the physician
Alemacon of Crotona, and taught by the great Hippocrates in the fifth
and by Plato in the fourth century, Aristotle's prejudices in favour of
the doctrines of a different school of biologists led him to revert to
the view that it is the heart which is the centre of what we now call
the "nervous system." It is mainly on account of these reactionary
scientific views that he was attacked in the early seventeenth century
by writers like our own Francis Bacon, who found in veneration for
Aristotle one of the chief hindrances to the free development of natural
science. The same complaints had been made long before by critics
belonging to the Platonic Academy. It is a Platonist of the time of
Marcus Aurelius who sums up a vigorous attack on the Aristotelian
astronomy by the remark that Aristotle never understood that the true
task of the physicist is not to prescribe laws to Nature, but to learn
from observation of the facts what the laws followed by Nature are.
In determining the scope of Physics, we have to begin by considering
what is the special characteristic of things produced by Nature as
contrasted with those produced by "art." The obvious distinction,
intimated by the very etymology of the word "Nature" (_physis_,
connected with _phyesthai_, to grow, to be born, as _natura_ is with
_nasci_), is that "what is by Nature" is born and grows, whereas what is
as a result of artifice is _made_. The "natural" may thus be said to
consist of living bodies and of their constituent parts. Hence
inorganic matter also is included in "Nature," on the ground that living
tissue can be analysed back into compounds of the "elements." Now
things which are alive and grow are distinguished from things which are
made by "a source of motion and quiescence within themselves"; all of
them exhibit motions, changes of quality, processes of growth and
decline which are initiated from within. Hence Nature may be defined as
the totality of things which have a source of motion internal to
themselves and of the constituent parts of such things. Nature then
comprises all beings capable of spontaneous change. Whatever either does
not change at all, or only changes in consequence of external
influences, is excluded from Nature.
Thus the fundamental fact everywhere present in Nature is "change,"
"process," "motion." Since motion in the literal sense of change of
position is involved as a condition of every such process, and such
motion requires space through which to move and time to move in, the
doctrine of space and time will also form part of Physics. Hence a
great part of Aristotle's special lectures on Physics is occupied with
discussion of the nature of space and time, and of the continuity which
we must ascribe to them if the "continuous motion" on which the unbroken
life of the universe depends is to be real Aristotle knows nothing of
the modern questions whether space and time are "real" or only
"phenomenal," whether they are "objective" or "subjective." Just as he
simply assumes that bodies are things that really exist, whether we
happen to perceive them or not, so he assumes that the space and time in
which they move are real features of a world that does not depend for
its existence on our perceiving it.
His treatment of space is singularly _naif_. He conceives it as a sort
of vessel, into which you can pour different liquids. Just as the same
pot may hold first wine and then water, so, if you can say, "there was
water here, but now there is air here," this implies the existence of a
receptacle which once held the water, but now holds the air. Hence a
jug or pot may be called a "place that can be carried about," and space
or place may be called "an immovable vessel." Hence the "place" of a
thing may be defined as the boundary, or inner surface, of the body
which immediately surrounds the thing. It follows from this that there
can be no empty space. In the last resort, "absolute space" is the
actual surface of the outermost "heaven" which contains everything else
in itself but is not contained in any remoter body. Thus all things
whatever are "in" this "heaven." But it is not itself "in" anything
else. In accord with the standing Greek identification of determinate
character with limitation, Aristotle holds that this outermost heaven
must be at a limited distance from us. Actual space is thus finite in
the sense that the volume of the universe could be expressed as a finite
number of cubic miles or yards, though, since it must be "continuous,"
it is infinitely divisible. However often you subdivide a length, an
area, or a volume, you will always be dividing it into lesser lengths,
&c., which can once more be divided. You will never by division come to
"points," _i.e._ mere positions without magnitude of divisibility.
The treatment of time is more thoughtful. Time is inseparably connected
with movement or change. We only perceive that time has elapsed when we
perceive that change has occurred. But time is not the same as change.
For change is of different and incommensurate kinds, change of place,
change of colour, &c.; but to take up time is common to all these forms
of process. And time is not the same as motion. For there are
different rates of speed, but the very fact that we can compare these
different velocities implies that there are not different velocities of
_time_. Time then is that in terms of which we _measure_ motion, "the
number of motion in respect of before and after," _i.e._ it is that by
which we estimate the _duration_ of processes. Thus _e.g._ when we
speak of _two_ minutes, _two_ days, _two_ months as required for a
certain process to be completed, we are counting something. This
something is time. It does not seem to occur to Aristotle that this
definition implies that there are indivisible bits of time, though he
quite correctly states the incompatible proposition that time is "made
up of successive _nows_," _i.e._ moments which have no duration at all,
and can no more be counted than the points on a straight line. He
recognises of course that the "continuity" of motion implies that of
time as well as of space. Since, however, "continuity" in his language
means the same thing as indefinite divisibility, it ought not to be
possible for him to regard time as "made up of _nows_"; time, like
linear extension, ought for him to be a "length of" something.
*The Continuous Motion and the "Spheres."*--The continuous world-process
depends upon a continuous movement set up in the universe as a whole by
the presence of an everlasting and unchangeable "First Mover," God.
From the self-sameness of God, it follows that this most universal of
movements must be absolutely uniform. Of what precise kind can such a
movement be? As the source of the movement is one, and the object moved
is also one--viz. the compass of the "heaven," the movement of the
_primum mobile_ or "first moved"--the object immediately stimulated to
motion by God's presence to it, must be mechanically simple. Now
Aristotle, mistakenly, held that there are two forms of movement which
are simple and unanalysable, motion of translation along a straight
line, and motion of rotation round an axis. He is at pains to argue
that rectilinear motion, which we easily discover to be that
characteristic of bodies near the earth's surface when left to
themselves, cannot be the kind of movement which belongs to the "heaven"
as a whole. For continuous rectilinear movement in the same direction
could not go on for ever on his assumption that there is no space
outside the "heaven," which is itself at a finite distance from us. And
motion to and fro would not be unbroken, since Aristotle argues that
every time a moving body reached the end of its path, and the sense of
its movement was reversed, it would be for two consecutive moments in
the same place, and therefore at rest. Reversal of sense would imply a
discontinuity. Hence he decides that the primary unbroken movement must
be the rotation of the "first moved"--that is, the heaven containing the
fixed stars--round its axis. This is the only movement which could go
on for ever at a uniform rate and in the same sense. Starting with the
conviction that the earth is at rest in the centre of the universe, he
inevitably accounts for the alternation of day and night as the effect
of such a revolution of the whole universe round an axis passing through
the centre of the earth. The universe is thus thought of as bounded by
a spherical surface, on the concave side of which are the fixed stars,
which are therefore one and all at the same distance from us. This
sphere, under the immediate influence of God, revolves on its axis once
in twenty-four hours, and this period of revolution is absolutely
uniform. Next the apparently irregular paths of the "planets" known to
Aristotle (_i.e._ the moon, Mercury, Venus, the sun, Mars, Jupiter,
Saturn) are resolved into combinations of similar uniform rotations,
each planet having as many "spheres" assigned to it as are requisite for
the analysis of its apparent path into perfectly circular elementary
motions. Altogether Aristotle holds that fifty-four such rotating
spheres are required over and above the "first moved" itself, whose
rotation is, of course, communicated to all the lesser "spheres"
included within it. As in the case of the "first moved," the uniform
unceasing rotation of each "sphere" is explained by the influence on it
of an unchanging immaterial "form," which is to its own "sphere" what
God is to the universe as a whole. In the Aristotelianism of the
mediaeval church these pure forms or intelligences which originate the
movements of the various planetary spheres are naturally identified with
angels. It is _e.g._ to the angelic intelligences which "move" the
heaven of Venus, which comes third in order counting outward from the
earth, that Dante addresses his famous Canzone, _Voi ch' intendendo il
terzo del movete_. The mediaeval astronomy, however, differs in two
important respects from that of Aristotle himself. (1) The number of
"spheres" is different. Increasing knowledge of the complexity of the
paths of the planets showed that if their paths are to be analysed into
combinations of circular motions, fifty-four such rotations must be an
altogether inadequate number. Aristotle's method of analysis of the
heavenly movements was therefore combined with either or both of two
others originated by pure astronomers who sat loose to metaphysics. One
of these methods was to account for a planet's path by the introduction
of _epicycles_. The planet was thought of not as fixed at a given point
on its principal sphere, but as situated on the circumference of a
lesser sphere which has its centre at a fixed point of the principal
sphere and rotates around an axis passing through this centre. If need
were, this type of hypothesis could be further complicated by imagining
any number of such epicycles within epicycles. The other method was the
employment of "eccentrics," _i.e._ circular movements which are
described not about the common centre of the earth and the universe, but
about some point in its neighbourhood. By combinations of epicycles and
eccentrics the mediaeval astronomers contrived to reduce the number of
principal spheres to _one_ for each planet, the arrangement we find in
Dante. (2) Also real or supposed astronomical perturbations unknown to
Aristotle led some mediaeval theorists to follow the scheme devised by
Alphonso the Wise of Castille, in which further spheres are inserted
between that of Saturn, the outermost planet, and the "first moved." In
Dante, we have, excluding the "empyrean" or immovable heaven where God
and the blessed are, nine "spheres," one for each of the planets, one
for the fixed stars, and one for the "first moved," which is now
distinguished from the heaven of the stars. In Milton, who adopts the
"Alphonsine" scheme, we have further a sphere called the "second
movable" or "crystalline" introduced between the heaven of the fixed
stars and the "first moved," to account for the imaginary phenomenon of
"trepidation."[#] In reading Dante, Shakespeare, and Milton, we have
always to remember that none of these reproduces the Aristotelian
doctrine of the "spheres" accurately; their astronomy is an amalgam of
Aristotle, Ptolemy, and Hipparchus.
[#] _Paradise Lost_, iii. 481.
"They pass the planets seven, and pass the fixed,
And that crystalline sphere whose balance weighs
The trepidation talked, and that first moved."