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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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