If the recognition of physics and logic as two studies co-ordinate with ethics is sufficient to differentiate the mature Zeno from the Cynic author of the Republic, no less than from his own heterodox disciple Aristo, the elaboration on all sides of Stoic natural philosophy belongs to Cleanthes, who cer tainly was not the merely docile and receptive intelligence he is sometimes represented as being. He carried on and completed the assimilation of Heraclitean doctrine ; but his own contributions were more distinctive and original than those of any other Stoic. He was able to transform Zeno's seeming dualism of God (or force) and formless matter into the lofty pantheism which breathes in every line of the famous hymn to Zeus. Heraclitus had indeed declared all to be in flux, but we ask in vain what is the cause for the unceasing process of his ever-living fire. It was left for Cleanthes to discover this motive cause in a conception fam iliar to Zeno, as to the Cynics before him, but restricted to the re gion of ethics—the conception of tension or effort. The soul of the sage, thought the Cynics, should be strained and braced for judg ment and action ; his first need is firmness (ebrovia) and Socratic strength. But the mind is a corporeal thing. Then followed the flash of genius : this varying tension of the one substance every where present, a purely physical fact, accounts for the diverse destinies of all innumerable particular things; it is the veritable cause of the flux and process of the universe. Herein lies the key to the entire system of the Stoics, as Cleanthes's epoch-making discovery continually received fresh applications to physics, ethics and epistemology.
Zeno had caught the practical spirit of his age— the desire for a popular philosophy to meet individual needs. But there was another tendency in post-Aristotelian thought—to lean upon authority and substitute learning for independent research— which grew stronger just in proportion as the fresh interest in the problems of the universe and the zeal for discovery declined—a shadow, we may call it, of the coming Scholasticism thrown a thousand years in advance. The representative of this tendency, Chrysippus, addressed himself to the congenial task of assimilat ing, developing, systematizing the doctrines bequeathed to him, and, above all, securing them in their stereotyped and final form, not simply from the assaults of the past, but, as after a long and successful career of controversy and polemical authorship he fondly hoped, from all possible attack in the future. To his per sonal characteristics can be traced the hair-splitting and formal pedantry which ever afterwards marked the activity of the school, the dry repellent technical procedure of the Dialecticians par excellence, as they were called. He created their formal logic and contributed much that was of value to their psychology and epis temology; but in the main his work was to new-label and new arrange in every department, and to lavish most care and atten tion on the least important parts—the logical terminology and the refutation of fallacies, or, as his opponents declared, the excogitation of fallacies which even he could not refute.
What is philosophy? No idle gratification of curiosity, no theory divorced from practice, no pursuit of science for its own sake, but knowledge so far forth as it can be realized in virtuous action, the learning of virtue by exer cise and effort and training. So absolutely is the "rare and price less wisdom" identical with virtue itself that the three main divisions of philosophy current at the time and accepted by Zeno —logic, physics and ethics—are defined as the most generic or comprehensive virtues. Accordingly Aristo rejected two of these parts of philosophy as useless and out of reach—a divergence which excluded him from the school, but strictly consistent with his view that ethics alone is scientific knowledge. Of the three divisions logic is the least important ; ethics is the outcome of the whole, and historically the all-important vital element ; but the foundations of the whole system are best discerned in the science of nature, which deals pre-eminently with the macrocosm and the microcosm, the universe and man, including natural theology and anthropology or psychology, the latter forming the direct introduction to ethics.
The Stoic system is in brief : (a) materialism, (b) dynamic materialism, lastly (c) monism or pantheism. (a) The first of these characters is described by anticipation in Plato's Sophist (246 C seq.), where, arguing with those "who drag every thing down to the corporeal"
the Eleatic stranger would fain prove to them the existence of something incorporeal, as follows. "They admit the existence of an animate body. Is soul then something existent
Yes. And the qualities of soul, as justice and wisdom—are they visible and tangible? No. Do they then exist? They are in a dilemma." Now, however effec tive against Plato's contemporary Cynics or Atomists, the reason ing is thrown away upon the Stoics, who take boldly the one horn of this dilemma. That qualities of bodies (and therefore of the
corporeal soul) exist they do not deny; but they assert most un compromisingly that they are one and all (wisdom, justice, etc.) corporeal. And they strengthen their position by taking Plato's own definition (247 D), namely "being is that which has the power to act or be acted upon," and turning it against him. For this is only true of Body; action, except by contact, is incon ceivable; and they reduce every form of causation to the efficient cause, which implies the communication of motion from one body to another. Again and again, therefore, only Body exists. The most real realities to Plato and Aristotle had been thought and the objects of thought, pas and vonret., whether abstracted from sensibles or inherent in "matter," as the incognizable basis of all concrete existence. But this was too great an effort to last long. Such spiritualistic theories were nowhere really maintained after Aristotle and outside the circle of his immediate followers. The reaction came and left nothing of it all; for five centuries the dominant tone of the older and the newer schools alike was frankly materialistic. "If," says Aristotle, "there is no other sub stance but the organic substances of nature, physics will be the highest of the sciences," a conclusion which passed for axiomatic until the rise of Neoplatonism. The analogues therefore of meta physical problems must be sought in physics; particularly that problem of the causes of things for which the Platonic idea and the Peripatetic "constitutive form" had been, each in its turn, received solutions. (b) But the doctrine that all existence is confined within the limits of the sensible universe—that there is no being save corporeal being or body—does not suffice to char acterize the Stoic system ; it is no less a doctrine of the Epicu reans. It is the idea of tension or tonicity as the essential attri bute of body, in contradistinction to passive inert matter, which is distinctively Stoic. The Epicureans leave unexplained the pri mary constitution and first movements of their atoms or elemen tal solids ; chance or declination may account for them. Now, to the Stoics nothing passes unexplained; there is a reason (XO-yos) for everything in nature. Everything which exists is at once capable of acting and being acted upon. In everything that exists, therefore, even the smallest particle, there are these two princi ples. By virtue of the passive principle the thing is susceptible of motion and modification ; it is matter which determines sub stance (oboia). The active principle makes the matter a given determinate thing, characterizing and qualifying it, whence it is termed quality (roams). For all that is or happens there is an immediate cause or antecedent ; and as "cause" means "cause of motion," and only body can act upon body, it follows that this antecedent cause is itself as truly corporeal as the matter upon which it acts. Thus we are led to regard the active principle "force" as everywhere coextensive with "matter," as pervading and permeating it, and together with it occupying and filling space. This is that famous doctrine of universal permeation (Kpao-ts 81. iiXov), by which the axiom that two bodies cannot occupy the same space is practically denied. Thus that harmony of separate doctrines which contributes to the impressive sim plicity of the Stoic physics is only attained at the cost of offending healthy common sense, for Body itself is robbed of a character istic attribute. 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 mate rial of these qualities, conceived as air-currents in various degrees of tension. We hear, too, of corporeal days and years, corporeal virtues, and actions (like walking) which are bodies
) Obviously, again, the Stoic quality corresponds to Aristotle's es sential form; in both systems the active principle, "the cause of all that matter becomes," is that which accounts for the existence of a given concrete thing (X6yos rijs oboias). Only here, instead of assuming something immaterial (and therefore unverifiable), we fall back upon a current of air or gas (rvcD,u,a); the essential reason of the thing is itself material, standing to it in the relation of a gaseous to a solid body. Here, too, the reason of things— that which accounts for them—is no longer some external end to which they are tending; it is something acting within them, "a spirit deeply interfused," germinating and developing as from a seed in the heart of each separate thing that exists (X6yos oirEpp.anKos). By its prompting the thing grows, develops and decays, while this "germinal reason," the element of quality in the thing, remains constant through all its changes.