stoic physics
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Stoic physics
In Stoic physics, the Earth and the universe are all part of a single
whole.
Stoic physics is the natural philosophy adopted by theStoic philosophers of ancient Greece and Rome used to
explain the natural processes at work in the universe. To
the Stoics the universe is a single pantheistic God, but
one which is also a material substance. The primitive sub-
stance of the universe is a divine essence ( pneuma) which
is the basis of everything which exists. The separation of
force from matter produces a divine fire (aether ) which,
as the basis of all matter, is differentiated into elements
and shaped by the tension caused by the pneuma work-
ing according to the divine reason (logos ) of the universe.
These processes are responsible for the formation, the de-
velopment, and ultimately, the destruction of the universe
in a never-ending cycle ( palingenesis ). The human soul
is an emanation from the fiery aether which permeates
the universe, and sensation is transmission of pneuma-
currents from objects, which interact with the substance
of the mind, which is the soul’s ruling part. The Sto-
ics also recognised the existence of other gods and di-
vine agents as manifestations of the one primitive God-
substance.
1 Doctrines
Stoic physics can be described in terms of (a)materialism,
(b) dynamic materialism, and (c) monism or pantheism.
1.1 Materialism
Philosophers since the time of Plato had asked whether
abstract qualities of the soul, such as justice and wisdom,
have an independent existence.[1] In particular, could
something that was not visible and tangible be said to ex-
ist. The Stoics’ answer to this dilemma was to assert that
everything, including wisdom, justice, etc., are corporeal.
Plato had defined being as “that which has the power to
act or be acted upon,”[2] and for the Stoics this meant
that all action proceeds by bodily contact; every form ofcausation is reduced to the efficient cause, which implies
the communication of motion from one body to another.
Only Body exists. Stoicism was thus fully materialistic;
the answers to metaphysics are to be sought in physics;
particularly the problem of the causes of things for which
the Platonic Theory of Forms and the Peripatetic “consti-
tutive form” had been put forth as solutions.
1.2 Dynamism
Materialism was also a doctrine of the Epicureans. Thecharacteristic difference with the Stoic system was the
idea of tension as the essential attribute of body. The
Epicureans placed the form and movement of matter in
the chance movements of primitive atoms. To the Stoics,
however, nothing passes unexplained; there is a reason
(Logos) for everything in nature. In everything that ex-
ists there are two principles, the active and the passive:
everything which exists is capable of acting and being
acted upon. By the passive principle a thing is susceptible
to motion and modification; matter determines substance
(ousia). The active principle characterizes matter, and
gives it its quality. For all that happens there is a cause,
and as only body can act on body, this cause is as corpo-
real as the matter upon which it acts. The active principle
or “force” is everywhere coextensive with “matter,” per-
vading and permeating it, and, together with it, occupy-
ing and filling space. A thing is no longer, as Plato once
thought, hot or hard or bright by partaking in abstract heat
or hardness or brightness, but by containing within its own
substance the material of these qualities, conceived as
air-currents ( pneuma) in various degrees of tension. The
virtues are corporeal, as indeed are actions. The Stoic
quality corresponds to Aristotle's essential form; in both
systems the active principle, “the cause of all that matter
becomes,” is that which accounts for the existence of agiven concrete thing, but in the Stoic system, the princi-
ple is itself material. Here, too, the reason of things –
1
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2 2 COSMOGONY
that which accounts for them – is no longer some exter-
nal end to which they are tending; it is something acting
within them, “a spirit deeply interfused,” germinating and
developing from within. By its prompting a thing grows,
develops and decays, while this “seminal reason,” the ele-
ment of quality in the thing, remains constant through all
its changes.
1.3 Monism
As to the relation between the active and the passive prin-
ciples there was no real difference. The active cause was
always a corporeal current, and therefore matter, although
the finest and subtlest matter. Aristotle’s technical term
Form (ethos ) the Stoics never used, but always Reason or
God. The Stoics laid down with rigid accuracy the two
chief properties of matter – extension in three dimen-
sions, and resistance, both being traced back to force.There were, it is true, certain conceptions, creations of
thought to which nothing real and external corresponded,
such as time, space, and void, but though each of these
might be said to be something, they could not be said to
exist.
A Stoic might maintain that World-Soul, Providence,
Destiny and Seminal Reason are not mere synonyms, for
they express different aspects of God or different rela-
tions of God to things, but there were no different sub-
stances underlying the different forces of nature. The
pneuma neither increases nor diminishes; but its modes of
working, its different currents, can be conveniently dis-tinguished and enumerated as evidence of so many dis-
tinct attributes.
2 Cosmogony
The pneuma of the Stoics is the primitive substance which
existed before the universe. It is the everlasting presup-
position of particular things; the totality of all existence;
out of it the whole visible universe proceeds, eventually
to be consumed by it. It is the creative force (God) which
develops and shapes the universal order (cosmos). Godis everything that exists.
In the original state, the pneuma-God and the universe
are absolutely identical; but even then tension, the es-
sential attribute of matter, is at work. In the primitive
pneuma there resides the utmost heat and tension, within
which there is a pressure, an expansive and dispersive ten-
dency. The pneuma cannot long withstand this intense
pressure. Motion backwards and forwards once set up
cools the glowing mass of fiery vapour and weakens the
tension. Thus follows the first differentiation of primi-
tive substance – the separation of force from matter, the
emanation of the world from God. The seminal Logos which, in virtue of its tension, slumbered in pneuma, now
proceeds upon its creative task. The primitive substance
In Stoic physics, the universe is shaped by a divine artisan-fire.
is not Heraclitus's fire, but rather it is a fiery breath or
aether , a spiritualized element. The cycle of its transfor-
mations and successive condensations constitutes the life
of the universe. The universe and all its parts are onlydifferent embodiments and stages in the change of prim-
itive being which Heraclitus had called a progress up and
down.[3] Out of it is separated, first, elemental fire, the
fire which we know, which burns and destroys; and this,
again, condenses into air or aerial vapour; a further step
in the downward path produces water and earth from the
solidification of air. At every stage the degree of tension
is slackened, and the resulting element approaches more
and more to “inert” matter. But, just as one element does
not wholly transform into another (e.g. only a part of air is
transmuted into water or earth), so the pneuma itself does
not wholly transform into the elements. The residue that
remains in original purity with its tension is the ether in
the highest sphere of the visible heavens, encircling the
world of which it is lord and head. From the elements
the one substance is transformed into the multitude of in-
dividual things in the orderly universe, which is itself a
living thing or being, and the pneuma pervading it, and
conditioning life and growth everywhere, is its soul. But
this process of differentiation is not eternal; it continues
only until the times of the restoration of all things. For
the world which has grown up will in turn decay. The
tension which has been relaxed will again be tightened;
things will gradually resolve into elements, and the ele-
ments into the primary substance, to be consummated ina general conflagration (ekpyrôsis) when once more the
world will be absorbed in God. Then in due order a new
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cycle of the universe begins, reproducing the previous,
and so on forever.
Zeno of Citium, founder of the Stoic school
The influence of Heraclitus upon Stoicism is a matter of
dispute, but the earliest Stoics, such as Cleanthes, Aristo
and Sphaerus all wrote commentaries on the writings of
Heraclitus,[4] which point to a common study of thesewritings under Zeno. In Heraclitus the constant flux is a
metaphysical notion replaced by the interchange of mate-
rial elements which Chrysippus stated as a simple propo-
sition of physics. Heraclitus offers no analogy to the doc-
trine of four elements as different grades of tension; to
the conception of “fire” and “air” as the “form” of partic-
ulars; nor to the function of organizing fire which works
by methodic plan to produce andpreserve the world. Nor,
again, is there any analogy to the peculiar Stoic doctrine
of universal intermingling.
In Stoicism every character and property of a particular
thing is determined solely by the tension in it of a cur-rent of pneuma, and pneuma, though present in all things,
varies indefinitely in quantity and intensity. So condensed
and coarsened is the indwelling pneuma of inorganic bod-
ies that no trace of elasticity or life remains; it cannot even
afford them the power of motion; all it can do is to hold
them together, pneuma is present in stone or metal as a
retaining principle. In plants it is manifested as some-
thing far purer and possessing greater tension, called a
“nature,” or principle of growth. A distinction was drawnbetween irrational animals, and the rational, i.e. gods and
humans, leaving room for a divergence, or rather devel-
opment, of Stoic opinion. The older authorities conceded
a vital principle, but denied a soul, to the animals. Later
on it was a Stoic tenet to concede a soul, though not a
rational soul, throughout the animal kingdom. The uni-
versal presence of pneuma was confirmed by observation.
A certain warmth, akin to the vital heat of organic being,
seems to be found in inorganic nature: vapours from the
earth, hot springs, sparks from the flint, were claimed as
the last remnant of pneuma not yet utterly slackened and
cold. They appealed also to the speed and expansion ofgaseous bodies, to whirlwinds and inflated balloons.
The Logos is quick and powerful, and sharper than any
two-edged sword. Tension itself Cleanthes defined as a
fiery stroke; in his Hymn to Zeus lightning is the symbol of
divine activity. As to the fundamental properties of body,
extension and resistance, extension results from distance;
but distances, or dimensions, are straight lines, i.e. lines
of greatest tension. Tension produces expansion, or in-
crease in distance. Resistance, again, is explained by
cohesion, which implies binding force. Again, the pri-
mary substance has rectilinear motion in two directions,
backwards and forwards, at once a condensation, whichproduces cohesion and substance, and an expansion, the
cause of extension and qualities.
3 Soul
In the rational creatures – humans and gods – pneuma is
manifested in a high degree of purity and intensity as an
emanation from the world-soul , itself an emanation from
the primary substance of purest aether – a spark of the
celestial fire, or, more accurately, fiery breath, character-
ized by vital warmth more than by dryness.
The soul is corporeal, else it would have no real existence,
would be incapable of extension in three dimensions (and
therefore of equable diffusion all over the body), inca-
pable of holding the body together, herein presenting a
sharp contrast to the Epicurean tenet that it is the body
which confines and shelters the atoms of soul. This cor-
poreal soul is reason, mind, and ruling principle; in virtue
of its divine origin Cleanthes can say to Zeus, “We too are
thy offspring,” and Seneca can calmly insist that, if man
and God are not on perfect equality, the superiority rests
rather on our side.[5] What God is for the world, the soul is
for humans. The cosmos is a single whole, its variety be-ing referred to varying stages of condensation in pneuma.
So, too, the human soul must possess absolute simplicity,
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4 4 SENSATION
its varying functions being conditioned by the degrees of
its tension. It follows that of “parts” of the soul, as previ-
ous thinkers imagined, there can be no question; all that
can consistently be maintained is that from the centre of
the body – the heart – distinct air-currents are discharged
to various organs, which are so many modes of the one
soul’s activity.
With this psychology is intimately connected the Stoic
theory of knowledge. From the unity of soul it follows
that all mental processes – sensation, assent, impulse –
proceed from reason, the ruling part; the one rational soul
alone has sensations, assents to judgments, is impelled to-
wards objects of desire just as much as it thinks or rea-
sons. Not that all these powers at once reach full maturity.
The soul at first is empty of content; in the embryo it has
not developed beyond the nutritive principle of a plant;
at birth the “ruling part” is a blank tablet, although ready
prepared to receive writing. This excludes all possibility
of innate ideas or any faculty akin to intuitive reason. Thesource of all our knowledge is experience and discursive
thought, which manipulates the materials of sense. Our
ideas are copied from stored-up sensations.
Just as a relaxation in tension brings about the dissolution
of the universe; so in the body, a relaxation of tension,
accounts for sleep, decay, and death for the human body.
After death the disembodied soul can only maintain its
separate existence, even for a limited time, by mount-
ing to that region of the universe which is akin to its na-
ture. It was a moot point whether all souls so survive,
as Cleanthes thought, or the souls of the wise and good
alone, which was the opinion of Chrysippus; in any case,sooner or later individual souls are merged in the soul of
the universe, from which they originated.
The relation of the soul of the universe to God is quite
clear: it is an inherent property, a mode of its activity,
an emanation from the fiery aether which permeates the
universe.
4 Sensation
The Stoics explained perception as a transmission of the
perceived quality of an object, by means of the sense or-
gan, into the percipient’s mind. The quality transmitted
appears as a disturbance or impression upon the corpo-
real surface of that “thinking thing,” the soul. In the ex-
ample of sight, a conical pencil of rays diverges from the
pupil of the eye, so that its base covers the object seen.
A presentation is conveyed, by an air-current, from the
sense organ, here the eye, to the mind, i.e. the soul’s “rul-
ing part.” The presentation, besides attesting its own ex-
istence, gives further information of its object – such as
colour or size. Zeno and Cleanthes compared this pre-
sentation to the impression which a seal bears upon wax,while Chrysippus determined it more vaguely as a hid-
den modification or mode of mind. But the mind is no
mere passive recipient of impressions from without. Sen-
sation reacts, by a variation in tension, against the cur-
rent from the sense-organ; and this is the mind’s assent
or dissent, which is inseparable from the sense presenta-
tion. The contents of experience are not all true or valid:
hallucination is possible; here the Stoics agreed with the
Epicureans. It is necessary, therefore, that assent shouldnot be given indiscriminately; we must determine a cri-
terion of truth, a special formal test whereby reason may
recognize the merely plausible and hold fast the true.
Chrysippus of Soli
The earlier Stoics made right reason the standard of
truth.[6] The law which regulates our action is thus the ul-
timate criterion of what we know – practical knowledge
being understood to be of paramount importance. But
this criterion was open to the persistent attacks of Epi-
cureans and Academics, who made clear (1) that reason is
dependent upon, if not derived from, sense, and (2) that
the utterances of reason lack consistency. Chrysippus,therefore, substituted for the Logos the new standards of
sensation and general conception, and more clearly de-
fined and safeguarded his predecessors’ position. For rea-
son is consistent in the general conceptions in which all
people agree. Nor was the term sensation sufficiently
definite. Chrysippus fixed upon a certain characteristic
of true presentations; provided the sense organ and the
mind be healthy, provided an external object be really
seen or heard, the presentation, in virtue of its clearness
and distinctness, has the power to extort the assent which
it always lies in our power to give or to withhold.
The work of reason was assimilated to the force whichbinds together the parts of an inorganic body and resists
their separation. There is nothing in the order of the uni-
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verse other than extended mobile bodies and forces in
tension in these bodies. So, too, in the order of knowl-
edge there is nothing but sense and the force of rea-
son maintaining its tension and connecting sensations and
ideas in their proper sequence. Zeno compared sensa-
tion to the outstretched hand, flat and open; bending the
fingers was assent; the clenched fist was “simple appre-hension,” the mental grasp of an object; knowledge was
the clenched fist tightly held in the other hand.[7] The il-
lustration is valuable for the light it throws on the essential
unity of diverse intellectual operations as well as for en-
forcing once more the Stoic doctrine that different grades
of knowledge are different grades of tension. Good and
evil, virtues and vices, remarked Plutarch, are all capa-
ble of being perceived; sense, this common basis of all
mental activity, is a sort of touch by which the ethereal
pneuma which is the soul’s substance recognizes and mea-
sures tension.
5 Gods
For the Stoics, God is everywhere as the ruler and up-
holder, and at the same time the law, of the universe.
Zeno declared cult images, shrines, temples, sacrifices,
prayers and worship to be of no avail. A really accept-
able prayer, he taught, can only have reference to a virtu-
ous and devout mind. The Stoics however attempted to
defend and uphold the truth in polytheism. Not only wasthe primitive substance God, the one supreme being, but
divinity could be ascribed to the manifestations – to the
heavenly bodies, which were conceived, like Plato’s cre-
ated gods, as the highest of rational beings, to the forces
of nature, even to deified men; and thus the world was
peopled with divine agencies.
6 Divination
The practice of divination and the consultation of oracles
afforded a means of communication between God and
man – a concession to popular belief, which may be ex-
plained when we reflect that divination was an essential
element of Greek religion. Chrysippus did his best to
reconcile the superstition with his own rational doctrine
of strict causation. Omens and portents, he explained, are
the natural symptoms of certain occurrences. There must
be countless indications of the course of providence, for
the most part unobserved, the meaning of only a few hav-
ing become known to humanity. To those who argued
that divination was superfluous as all events are foreor-
dained, he replied that both divination and our behaviourunder the warnings which it affords are included in the
chain of causation.
7 Notes
[1] Plato, Sophist , 246C ff.
[2] Plato, Sophist , 247D
[3] Heraclitus, DK B60
[4] Diogenes Laërtius, vii. 174, ix. 5, 15
[5] Seneca, Epistles , liii. 11–12
[6] Diogenes Laërtius, vii. 54
[7] Cicero, Academica, ii. 4
8 References
• This article incorporates text from a publication now
in the public domain: R.D. Hicks (1911). “Stoics”.In Chisholm, Hugh. Encyclopædia Britannica (11th
ed.). Cambridge University Press.
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