Katerina Ierodiakonou provides a very handy overview of the ancient Greek philosophical concept of sympatheia, in her article The Greek Concept of Sympatheia and Its Byzantine Appropriation in Michael Psellos, which appears as the second chapter in the anthology The Occult Sciences in Byzantium, edited by Magdalino and Mavroudi (here is the book at googlebooks - most of this chapter can be viewed there):
A. In ancient Greek sympatheia has different, though obviously interrelated, meanings: it is used in medical writings, as for example in the Hippocratic corpus (De alim. 23.1), to refer to the fact that when a part of the human body somehow suffers another part may be affected, too; it is also used to talk about the fact that people may share the feelings of their fellow citizens, for instance in Aristotle's Politics (1340a13); finally, it is used to refer to the supposed phenomenon that all beings on earth and in the heavens are inextricably linked together. That is to say, the ancient notion of sympatheia indicates a close connection between things which are parts of some kind of a whole, either at the same level, as different parts of the body are in relation to the body as a whole, or at different levels, as the body and soul are in relation to the living being as a whole. Thus sympatheia could refer to the close connection between different parts of the same body as a whole, or the close connection between everything in the world as a part of the world as a whole, or between the body of the world and its soul as parts of the world.Note the three different uses of sumpatheia (and also note that Ierodiakonou states that these three uses are "obviously interrelated"): (1) in medicine to describe the relationship between different parts of the body, (2) to describe shared feelings among human beings, and (3) to describe the phenomenon by which everything in the universe is inextricably linked together. Ierodiakonou calls this last kind of sympatheia (which includes "the close connection ... between the body of the world and its soul as parts of the world") cosmic sympatheia, about which she says:
B. The notion of cosmic sympatheia was introduced by the Stoic philosophers in the Hellenistic period. Some scholars have attributed the full development of this notion to Posidonius at the end of the second and beginning of the first century BC [see especially K. Reinhardt, Kosmos und Sympathie], but there is no doubt that even the early Stoics, and in particular Chrysippus, believed in a close affinity among the different parts of the universe; and for this close affinity they most probably used the term sympatheia, as well as the nouns synecheia or synochem symphyia, symmone, sympnoia, syntonia, and the corresponding verbs and adjectives. According to the Stoics there is nothing particularly mysterious about sympatheia, and especially about the relation between the things in the heavens and those on earth. In Stoic physics the whole cosmos is presented as a perfect living body whose parts, though, are imperfect, insofar as they are not self-sufficient and autonomous; for they cannot function by themselves and always depend on their being parts of this whole and its other parts. What holds the system together is a certain internal tension, a tonos, created in the universe by the so-called pneuma, which consists of a mixture of fire and air and permeates the entire world as its soul, sustaining everything. Thus the Stoics thought of the world as a unified living organism, a zoon: just as pneuma permeates a human body and makes it as its soul a living and organic whole, with each single part grown together in a close connection with all the rest, in the same way the whole world is permeated and given life by pneuma; this pneuma the Stoics identified with God who, in creating the world, becomes its soul.Ierodiakonou has packed quite a lot into that paragraph! First she states the commonly held (and more or less correct) position that sumpatheia is a Stoic concept. And then she reports, without endorsing, the commonly held (and more or less misleading) position that the "full development" of sumpatheia is due to Posidonius, for which she cites the work of Karl Reinhardt. As Ierodiakonou correctly points out "there is no doubt that even the early Stoics, and in particular Chrysippus, believed in a close affinity among the different parts of the universe; and for this close affinity they most probably used the term sympatheia." Posidonius is routinely cited as the first clear cut case of a philosopher using the term sympatheia in the sense of "cosmic sympathy", but, as Ierodianokou strongly implies, this is almost certainly an artifact of the extremely fragmentary nature of the extant primary sources from earlier (prior to Posidonius) Stoics.
Here is what P.A. Meijer has to say in his Stoic Theology on the concept of sumpatheia and its origins, based on the writings of Cicero and Sextus:
C. There is an elaborate argument which develops the idea of the coherence of the universe, because there is everywhere the all encompassing power. It unites the things in this world and the natural events, which follow each other in an eternally repeating ordered motion.And here is part of the passage from Sextus (his Against the Physicists, I 78 ff.) that Meijer is referring to (see Meijer, or the original, for the complete passage):
We have this argument in Sextus and a limited version in Cicero. Scholars more or less agree that this argument is to be ascribed to Chrysippus [one of the early founders of Stoicism, predating Posidonius by about a century]. This most interesting argument is not only important as a typical piece of Stoic philosophy, but it has largely influenced later Greek philosophy, i.e. Neoplatonism, by its stressing the unity in this world. Unity as a consequence of the influence of the One was a favorite theme in Plotinus.
D. Of bodies some are unified, some are formed of things conjoined, some of separate things. Unified bodies are such as are dominated by one structure, such as plants and animals. Those formed of conjoined parts are such as are composed of adjacent elements which tend to combine into one main structure, like cables, turrets and ships. Those formed of separate things are such as compounded of things which are disjoined and isolated and existing by themselves. like armies and flocks and choruses. Since the cosmos is also a body, it is either unified or of conjoined or of separate parts.In his De Natura Deorum (II 19) Cicero speaks of "the harmony, unanimity, and unbroken affinity in nature" and then provides several examples of this, such as "the diverse courses of the stars [being] maintained in the single rotation of the entire heavens" and then he says "these processes could not take place through harmonious activity in all parts of the universe, unless they were each embraced by a single divine, all pervading, spiritual force [pneuma]".
But it [the cosmos] is neither of conjoined nor of separate parts, as we proved from the sympathies it exhibits. For in accordance with the waxings and wanings of the moon many sea and land animals wane and was and ebb-tides and flood-tides occur in some parts of the sea. And in the same way, too, in accordance with certain risings and settings of the stars alterations in the surrounding atmosphere and all varieties of change in the air take place, sometimes for the better, sometimes fraught with pestilence. And from these facts it is obvious that the cosmos is a unified body. For in the cases of bodies formed from conjoined or separate elements the parts do not 'sympathize' with one another, since if all the soldiers, say, in an army have perished (save one), the one who survives is not seen to suffer at all through transmission; but in the case of unified bodies there exists a certain sympathy, since when the finger is cut, the whole body shares in its condition. So then, also the cosmos is a unified body.
Although it offers fewer details, Meijer is right in saying that Cicero's version is more "typically Stoic in that it describes the superior divine power as breath, pneuma. Pneuma is the Stoic element that causes structure in the inorganic, forms the psyche in animals and is also responsible for the mind in men. So it is the cause for the coherence of all things." Meijer also adds that this "concept of pneuma is characteristic of Chrysippus' thought." The point of this being that we needn't (and probably shouldn't) view cosmic sympathy as some later innovation by Posidonius, but rather as part of the foundational teachings of Stoicism qua Stoicism.
Returning now to Ierodiakonou (the passage labeled B above), she goes on to say that "there is nothing particularly mysterious about sympatheia, and especially about the relation between the things in the heavens and those on earth." Ierodiakonou doesn't tell us precisely (or even approximately) what she means by "mysterious", but later on (see passage E below) it will become evident that she is here imposing her own anachronistic (mis-) understanding of Stoic physicalism -- in particular she is conflating the very subtle ancient conception of physicalism (shared, in different forms, by the Stoics and Epicureans) with the much more narrow and crude modern conception of materialism. At the same time she is trying to draw a straight bright line between the supposed "dualism" of the Platonists and the physicalism of the Stoics, with the assumption that Stoic physicalism is not "mysterious" whereas Platonic "dualism" is.
After her cursory exorcising of all "mystery" from Stoic sumpatheia, Ierodiakonou goes on to write that "In Stoic physics the whole cosmos is presented as a perfect living body whose parts, though, are imperfect, insofar as they are not self-sufficient and autonomous." This is not only a correct statement about Stoic physics, it is also practically a direct quote from Plato's Timaeus. A little further down she acknowledges that the cosmological view that "the universe is a unified whole" in which "even parts of it which are separated by a large distance may affect each other in a conspicuous way" [see passage E below] is to be found in Plato's Timaeus. However, she fails to point out that Plato also wrote in the Timaeus that the universe as a whole is perfect and self-sufficient, while the parts of the universe are not. The Stoics are also in agreement with the Timaeus in that the universe as a whole is divine. In a word, Ierodiakonou, even while acknowledging some of the similarities, systematically exaggerates the differences between Platonic and Stoic cosmology.
Now here is one last passage from Ierodiakonou:
E. The Platonists were influenced by the Stoic notion of cosmic sympatheia to such an extent that it is only possible to fully grasp their use of the notion against its Stoic background. They also, following in this Plato's Timaeus, stressed the fact that the universe is a unified whole, and they also assumed that even parts of it which are separated by a large distance may affect each other in a conspicuous way, while the intervening parts seem unaffected. Plotinus, for instance, like Plato and the Stoics, thought of the world as living organism. Nevertheless, the Platonists' understanding of cosmic sympatheia significantly differs in certain respects from that of the Stoics. For their supreme God is transcendent and not part of the world, the way the Stoic God is immanent. In addition, on their view there is a sharp distinction between the material and immaterial world, of which the material world is a living image. Hence the Platonists strongly opposed the Stoics' doctrine of a direct commingling of the Divine with matter; they claimed that the Divine rather employs in the formation of the world certain incorporeal powers.First of all Ierodiakonou clearly overstates the Stoic "ownership" of the concept of sympatheia -- and she does so in a very bizarre way. Apparently forgetting that she has previously acknowledged that Plato's Timaeus already contained a similar concept to sympatheia, Ierodiakonou now claims that later Platonists must have been "influenced" by Stoic sympatheia. In fact, by the time of Posidonius the situation was increasingly just the opposite: Stoics were more and more being influenced by Platonism. A. A. Long has expressed the opinion that Posidonius marked a transition from "Platonizing Stoics", who appropriated Plato's words and ideas for their own (Stoic) purposes, to "Stoicizing Platonists", who, like Posidonius, significantly blurred any clear distinction between the two schools.
The details of Ierodiakonou's arguments are what makes it so bizarre. In his Timaeus, Plato presented a view of the cosmos in which everything is inextricably linked to everything else. Obviously Plato presented this idea in the context of a universe containing both physical and non-physical "stuff". The Stoics, however, took Plato's cosmological vision, and retooled it to fit into their purely "physical" universe. Therefore when later Platonists, from Plotinus to Proclus (etc) are found to have had a notion of cosmic sympathy of the sort found in the Timaeus (that is, in a cosmos comprised of things both physical and non-physical), this doesn't at all imply that these later Platonists have "modified" the Stoic, physicalist, notion of sympatheia -- it only means that they are consistently Platonic in their cosmology. Plotinus, et al, may certainly have borrowed and built upon some of the Stoic refinements to the conception of cosmic sympathy, but nothing more than that is at work.
To understand late antique Platonism it is necessary to study Stoicism. At the same time it is absolutely essential to study Plato in order to be able to have any grasp of Stoicism. Nowhere is this more true than when it comes to the theory of cosmic sympathy: it turns out that Stoicism and Platonism are inextricably intertwined with each other, like everything else in the cosmos.