ARISTOTLE AND THE EARLIER PERIPATETICS vol.I by Eduard Zeller, B.F.C.Costelloe 1897

;
PHYSICS 473
*
most primitive and ancient bodies. Those, on the
contrary, which exhibit a composite movement, must be
formed by combination from them, and receive their
particular bias from the constituent which preponderates
in their composition. That which is natural is
always earlier than that which is opposed to nature and
violent. It follows that circular, and also rectilineal,
movement must be naturally fitted for some body or
other, the more so that rotation is the only unbroken and
interminable movement, and nothing that is
contrary
to nature fulfils these conditions. Accordingly there
must exist two sorts of simple bodies— the
one originally
destined for rectilineal, the other for circular, movement.
1 Eectilineal movement has opposite directions :
it is either upwards or downwards, passing from centre
to circumference, or «ice versa. Consequent!}', the bodies
which exhibit it
must be of opposite natures, destined
for the one or the other kind of motion :
be either light or heavy.
hand, exhibits no such contraries.
towards any point in the circumference.
that is, they must
Circular motion, on the other
It starts from any point
So the body
which is naturally qualified for it must likewise be without
contrariety.
It can neither be heavy nor light, since
it does not rise or fall, and in fact it cannot exhibit any
kind of rectilineal motion.
It is even impossible to communicate
either upward or downward motion to it by force,
since if the one were unnatural to it the other must 2 be
distinction between two realms already laid down (c. 2, 269, a,
of being is obvious from his 10, 14) as the basis of the diswhole
treatment of the subject, cussion (see p. 224, n. 3), %v hi
Cf. also p. 366, n. 1. ivarriov, which, when thus uni-
1
Be Calo, i. 2, 268, b, 14 sqq. versally expressed, is certainly
'
According to the principle open to dispute.
474 ARISTOTLE
its natural motion. 1
motion is
The body that is destined for circular
also without beginning or ending, subject to
neither increase nor diminution, neither impression nor
change. 2
comes into
being springs from its opposite, and everything
that
His argument for this is that everything that
perishes is resolved into the same
3 all increase
and decrease depend upon addition or subtraction
of the matter out of which a thing has grown, and therefore
that which, being without beginning, possesses no
such matter, cannot increase or decrease ;
all bodies,
finally, which alter, either increase or decrease, and where
there is no such process neither is there any alteration. 4
1
Ibid. c. 3, 269, b, 18-270, a,
] 2 ; nor can the position $(a /j.iv
yap ev84x*Tat ttjv &Wov ko! irepov
I sc. Kti'rjtriif KivuixOai] (c. 2, 269, a,
7) be accepted except provisionally
as of universal validity.
As is shown in the sequel, it is
inapplicable to the SEther. The
position upon which the latter
conclusion rests, (viz. that movement
in a circle has no opposite).
Aristotle, indeed, endeavours
(c. 4) further to establish by
special proofs. But he cannot
prove that the motion may not
be crooked or oblique ; for if we
have two opposite motions on
the same or on parallel lines
which deviate in opposite directions,
it does not make the
slightest difference whether the
lines are straight or circular.
Moreover, the courses of the
fixed stars and of the planets
are actually in opposite directions
; why may these bodies
not, then, consist of different
jetherial substance ? We are not
warranted, however, with Meyer
(Aristot. Thierhtnde, 393) in
casting a doubt upon Aristotle's
clearly expressed meaning, merely
on the ground of the actual
difficulties that beset the theory.
2
He says, De Orlo, i. 3, 270,
a, 13, b, 1 : ayevTjTOf teal citpQaprov
Kal avavl-es real ai/aKKoiayroi/, aiSioy
teal out' avfy}aiv %x ov °^Te fpOlfTtv,
d\A' ayhparov «al dvaXkoianov teal
awaBis. Cf. Metaph. viii. 4, 1044,
b, 7, xii. 1, 2, 1069, a, 30, b, 25.
3
On this point, cf. also p.
341 sq.
4
Be Ccelo, i. 3, 270, a, 13-35.
The immutability of the body
which has no opposite might have
been proved more simply and
conclusively from the proposition
(p. 341, and p. 353 sq. above)
that all change means transition
from one state into its opposite,
and that a thing can only be
operated upon by its opposite.
Aristotle, however, does not here
adopt this method, as his investigation
into the conception of
change and affection was not
published until later—in his