STOIC AND POSIDONIAN THOUGHT ON THE IMMORTALITY OF SOUL

What did Posidonius mean by the immortality of soul? Was his reference to the world soul only or also to individual souls, including human souls? Is Posidonius’ conception of immortal souls genuinely Stoic? In attempting to answer these questions, this article initially sets out to elucidate Posidonius’ response to Plato’s assertion of the soul’s immortality advanced at Phaedrus 245c. My discussion further relates a Stoic and possibly a Posidonian conception of souls’ perishability to a line of Stoic thought Posidonius would have inherited regarding destruction, in which Chrysippus notably developed an account of the perishability of all qualified souls. In outlining a plausible theory by which Posidonius might have held both to souls’ immortality and their perishing, this work attempts to reconstruct the meaning Posidonius might have attached to these terms in their likely context of intellectual exchange with Stoicism’s critics, notably Cicero. Attention to Posidonius’ arguments in this quasi-polemical context suggests the Stoic orthodoxy of his views, further demonstrating how Stoicism was capable of defusing a number of apparent contradictions between the postulates of souls’ immortality and perishing through positing sophisticated distinctions between these terms. This paper further advances the claim that Posidonius’ interpretation of Plato’s argument makes sense within a context of his reading of Plato’s dialogue. It is likely that Posidonius was motivated to draw on Plato in the Phaedrus in order to equate Plato’s ‘all soul’ with whatever is self-moving, yielding a Posidonian characterization of ‘deathlessness’ as the whole of self-moving soul.


STOIC AND POSIDONIAN THOUGHT ON THE IMMORTALITY OF SOUL
What did Posidonius mean by the immortality of soul? Was his reference to the world soul only or also to individual souls, including human souls? Is Posidonius' conception of immortal souls genuinely Stoic? In attempting to answer these questions, this article initially sets out to elucidate Posidonius' response to Plato's assertion of the soul's immortality advanced at Phaedrus 245c. My discussion further relates a Stoic and possibly a Posidonian conception of souls' perishability to a line of Stoic thought Posidonius would have inherited regarding destruction, in which Chrysippus notably developed an account of the perishability of all qualified souls. In outlining a plausible theory by which Posidonius might have held both to souls' immortality and their perishing, this work attempts to reconstruct the meaning Posidonius might have attached to these terms in their likely context of intellectual exchange with Stoicism's critics, notably Cicero. Attention to Posidonius' arguments in this quasi-polemical context suggests the Stoic orthodoxy of his views, further demonstrating how Stoicism was capable of defusing a number of apparent contradictions between the postulates of souls' immortality and perishing through positing sophisticated distinctions between these terms. This paper further advances the claim that Posidonius' interpretation of Plato's argument makes sense within a context of his reading of Plato's dialogue. It is likely that Posidonius was motivated to draw on Plato in the Phaedrus in order to equate Plato's 'all soul' with whatever is self-moving, yielding a Posidonian characterization of 'deathlessness' as the whole of self-moving soul.

I. 'IMMORTAL SOULS'
Hermias, in a passage of his commentary on Plato's Phaedrus, reports Posidonius' interpretation of Phaedrus 245c, where Plato uses the words to introduce his argument for the immortality of soul. In offering two contrasting interpretations of Plato's argument, Hermias singles out Posidonius as representative of the group who took the words to refer to 'the world soul only', in contrast with Harpocration, who supposedly took the term to refer to 'absolutely all' soul. Festugière's view aside, 1 Stoic scholarship has broadly advanced two views of this crux. Hoven suggests that Posidonius' reading represents a disinterested attempt to elucidate Plato without guidance from his own philosophy. Edelstein infers, contrarily, that Posidonius adopted his interpretation on the strength of his own belief in the immortality of the world soul only. Kidd largely concurs with this latter view, without finding adequate basis in Hermias' text for the inference. 2 In a competing attestation, Div. 1.64, however, Cicero reports that, in discussing the possibility of human dreams representing means of divination, Posidonius spoke of 'immortal souls'. Unless we distrust Cicero, it becomes difficult to infer both that Posidonius held to a belief that the world soul alone is immortal and that his interpretation of Plato was influenced by such a belief. In the light of Cicero's reference, the question of Posidonius' own view on the topic needs to be scrutinized further. Therefore I address this question first, before discussing Posidonius' interpretation of Plato's argument.
He proposes three ways in which men dream through divine impact: the mind of its own nature foresees, inasmuch as it is imbued with kinship with the gods; the air is full of immortal souls, in which appear, as it were, clear marks of truth; the gods themselves speak with men who are asleep.
(Cic. Div. 1.64; fr. 108 EK, part). 3 This Ciceronian attestation has given rise to extensive debate among scholars seeking to clarify Posidonius' apparent claim: 'the air is full of immortal souls'. Edelstein takes the expression 'immortal souls' to refer to the fixed stars, arguing further that 'it is impossible to conclude' from this assertion 'that Posidonius believed the human soul to be immortal'. 4 But in my view such a conclusion is not entirely impossible. In Cicero's testimony above, Posidonius' description of souls as immortal is not further specified, nor, to my knowledge, is there any evidence that Posidonius considered human souls mortal. Further, the words 'the air' seem to rule out the identification of 'souls' as the fixed stars; for the Stoics normally understood 'the sphere of the fixed stars [to be] created' not in the airy but in the fiery or ethereal region. Posidonius likewise associated the stars with 'the heaven', which he elsewhere called 'the outermost circumference', and which he and Chrysippus nominated as the dwelling-place of the cosmic deity and celestial gods. 5 In seeking to identify the 'souls' that are said by Posidonius to be in 'the air', we may need briefly to advert to the doxographical section of Sextus Empiricus, Math. 9.73-4. They [souls], having quitted the sphere of the sun, dwell in the region below the moon, and there because of the pureness of the air they remain for a long time, and for their nutrition they use the vapour rising from the earth, as do the rest of the stars also, and in those regions they have nothing to dissolve them. If, therefore, the souls remain, they come to be the same as daemons; and if there are daemons, then we must say that gods too exist, their existence being by no means hindered by the preconception about the legendary doings in Hades.  In the previous section 9.71-2, the same source, against Epicurus, insists upon the existence of souls in the extra-terrestrial region, in asserting that, after separating from their bodies, they neither move downwards nor are dispersed but 'rather soar lightly into the upper region'. The grounds for this argumentation rest both on the souls' causal effect upon themselves through their capacity of holding themselves together, and on their pneumatic nature, composed as they are out of airy and fiery fine particles. 6 In the present section just quoted, the passage's author further adduces arguments in favour of the souls' survival, citing in particular the air's pureness in the region below the moon.
Two points should be taken into account in considering the nature of these 'souls'. First, the author's demonstrations deploy a wide range of Stoic terms and ideas, for instance describing the souls as deriving nutrition from 'the vapour rising from the earth, as do the rest of the stars', 7 and even playing on the etymology of the word 'daemon' in the sentence 'if, therefore, the souls remain ( ), they come to be the same as daemons ( )'. 8 Further, the 'souls' considered in the Sextus passage are likely to refer to human souls surviving death, or more specifically to heroes; for only this assumption justifies the contention that the souls residing in the upper region for a long time 'come to be the same as daemons'.
This material preserved by Sextus, whoever his Stoic source, provides persuasive grounds for believing that the expression 'immortal souls' in 'the air', as suggested at Cicero, Div. 1.64, refers to daemons, that is, to divine souls intermediate between the stars and human beings, or to heroes, signifying the souls of dead virtuous men who have survived death. Perhaps both references are meant, seeing that for the author of the Sextus passage the expression 'the region below the moon' as the location of surviving human souls and daemons best parallels 'the air' in Cicero's report. The author is clear that the souls reside in this region 'because of the pureness of the air', which presumably facilitates their becoming the same as daemons. Kidd, in a passage of his commentary, makes a similar point to mine regarding Cicero's report; but this makes it hard to understand how and why Kidd elsewhere insists that 'Posidonius did believe in the sole immortality of the world soul'. 9 Posidonius' assertion in Cicero's report sufficiently confirms that he admitted the immortality of individual souls, in addition to that of the world soul.
There is a question, though, whether this Posidonian conception of the soul's immortality can legitimately be taken as Stoic, since a range of evidence presented below rather attests a Stoic conception of the perishability of souls. The Stoics, according to Diogenes Laertius 7.156, infer, 'first, that soul is a body', and, then, that it survives death; but it is perishable, though the soul of the universe, of which those [souls] in animals are parts, is imperishable. (Diog. Laert. 7.156) That is, for the Stoics, the world soul is identical to the whole of soul, whereas individual souls, such as those of animals, constitute its 'parts' ( ), as they were unified with the world soul during the conflagration, and are now, as Diogenes elsewhere reports, a fragment or an 'offshoot' ( ) of this soul, a formulation to which Posidonius seems to have taken no significant exception. 10 Further, Diogenes' doxography ascribes the idea of the soul surviving death but later perishing to the Stoics in general. In doing so, it draws our attention to two points. First, 'perishable' is a standard term used by Stoic writers to describe the nature of all individual souls, in implicit contrast to the 'imperishable' world soul. Second, the soul Diogenes here speaks of refers to individual souls generally, but more specifically to human souls, whether rational or irrational; for, to the best of my knowledge, Stoics as early as Zeno did not describe the souls of non-rational animals, the stars or daemons as surviving death.
Diogenes' doxography begins with general statements about souls advanced by the Stoics collectively, but afterwards cites Cleanthes as maintaining that 'all' souls survive up to the conflagration. Chrysippus, meanwhile, Diogenes asserts, holds this to be true only of the souls of sages. 11 Eusebius too, in his doxography of Stoic psychology, reports the same Chrysippean idea as Diogenes does, according to which, among the souls separated from their bodies, not all but only human souls survive on their own for a certain time; those of non-rational animals perish at once. Chrysippus appears to have maintained further that not even all human souls but only those of virtuous men survive up to the conflagration; fools' souls do so only for a limited period, perishing sooner. 12 The above evidence has two major implications. First, the Stoic assertion of souls' perishability should not be taken to mean that the souls are destroyed in an unqualified sense, but that they undergo a sort of natural change which the Stoics called broadly 'resolution', by which they are unified with the imperishable world soul so as to become its parts. Second, while believing individual souls to experience this resolution generally, Chrysippus, unlike Cleanthes, discriminated between the souls of sages and fools with regard to the mode of destruction. That is, for Chrysippus, sages' souls undergo the conflagration, whereas those of fools are not subject to this particular form of resolution, rather experiencing what might be called 'mere resolution'.
To make these points clearer, we should remember here that in Stoic physics 'resolution' holds a meaning far broader than that of 'conflagration', referring in Chrysippus' physics to a compound's dissolution into its components (for instance, an egg's dissolution into yolk, white and shell, etc). The Stoics further explained the dissolution of the world and its individuals into the four elements (fire, air, water and earth) as an instance of this kind of destruction, indicating more specifically 'rarefaction' or the reverse of condensation in the elements' reciprocal changes: ('Reciprocally, the dissolution and diffusion of earth, the first diffusion into water, and the second from water into air, and the third and last into fire'). 13 This last phase is still not identical with the conflagration, since ordinarily the rarefaction of air into fire occurs within a cyclical sequence proceeding immediately to condensation in its next stage, in which the world is partly rearranged.
The conflagration, on the other hand, is understood by the Stoics as the devastation of the world's arrangement as such, so that 'all', namely the whole of the world, is resolved into, and unified with, a single element 'fire'. 14 This process also represents a sort of rarefaction, but, unlike the normal referent of the term 'rarefaction', the conflagration is unidirectional and does not at once accompany condensation, rather determining the world's periodic destruction into fire at very long intervals of everlasting recurrence. In Stoic physics the conflagration is in this light a particular form of resolution, applying above all to the destruction of the elements, the world, the gods other than Zeus, and the souls of sages.
The question arises why Chrysippus believed that the souls of sages survived at all up to the conflagration, and what sense this made for him as a psychological or ethical doctrine, as well as a physical one. This question is controversial and I attempt no direct treatment of it here. But the extant Stoic evidence, however meagre, allows us to conjecture that, in Stoicism, among the souls separated from their bodies and changed into their lesser substance those of sages alone are able to survive up to the conflagration on the strength of their superiority both in intelligence and in pneumatic constitution. Presumably part of the answer to the above question lies in the Stoics' treatment of Plato's Phaedo as a canonical Socratic text, an attitude which meant that they had to extract from it lessons which could be made compatible with Stoicism. That is, total indestructibility of individual souls would have clashed with the conflagration theory, but limited 'indestructibility' as a reward for virtue could be made fully consistent with Stoicism. 15 This Chrysippean idea of the human soul's destruction, closely linked with his physics of the conflagration, probably represented a standard Stoic doctrine. Little evidence remains, however, as to how the post-Chrysippean Stoics responded to Chrysippus on the matter of souls' perishability. Inasmuch as Panaetius, siding with Boethus of Sidon and Diogenes of Babylon, denied the theory of the conflagration, it seems reasonable to suppose that Panaetius had no motive for following Chrysippus in every detail, preferring to use his own syllogisms in seeking to prove souls' perishability. 16 Posidonius at least differed from these three Stoics in abiding by the 116 earliest Stoic doctrine of the world's periodic destruction at the conflagration. 17 Further, as Arius Didymus' testimony shows, Posidonius, concurring also with mainstream Stoics, 18 held to a version of the theory classifying destruction into four types 19 : division, alteration, fusion and resolution, in Posidonius' wording 'an out-and-out-change', 20 attributing alteration to substance only and the other three modes to qualified individuals. Arius' doxography, however, provides no information as to Posidonius' examples. It thus remains a matter of speculation what forms of destruction he understood as applying to individual souls, and particularly to human souls.
This lack of direct evidence prevents us from fully recovering the terms of the debate inherited by Posidonius from Chrysippus on the topic of souls' perishability, and even whether such a debate existed at all. But in so far as Posidonius adhered to the standard Stoic doctrine of destruction as noted above, it is possible to suppose that he related individual souls to resolution, holding to an idea of perishable souls. On this supposition, however, in addition to the question of Posidonius' Stoic orthodoxy in insisting on souls' immortality, the compatibility for him between the postulates of souls' immortality and perishing also becomes a matter for discussion, especially when we bear in mind Cicero's objection to a Stoic belief in perishable souls on the basis of the immortality of soul.
Cicero, at Tusc. : 'Posidonius says that there are four kinds of destruction and generation from being to being. For, they recognized that there was no such thing as generation from, or destruction into, non-being, as we said before. But of change into being he says that one kind is by division ( ), one by alteration ( ), one by fusion ( ), and one an out-and-out change ( ), which they call "by resolution" ( ); of these, that by alteration belongs to the substance, while the other three belong to the so-called qualified individuals, which come to occupy the substance'. For the discussion of the testimony, see Long and Sedley (n. 12), 1.172-3; Kidd (n. 2), 1.384-90. Arius' doxography represents an important source for Posidonius' conception of generation and destruction. Posidonius' classification concerns less change as such than those changes by which a thing's identity can be lost, as Long and Sedley (see above) point out. Supposing that Arius' quotation is from a Posidonian source, possibly the word 'they' referred for Posidonius to mainstream Stoics, and the word 'we' suggests that he concurred with them on the definition of change. I will not discuss the question why Posidonius gave such a quadripartition, different from the Chrysippean ( ) as cited at Stob. Ecl. 1.17.4, p. 154 W (SVF 2.471), and also from the Stoic tripartition ( ) as cited at Philo, Aet. mund. 79. 20 As Arius' testimony (n. 19) shows, Posidonius called one sort of destruction 'an out-and-out change' ( ). It is uncertain why he introduced this new expression, on which Arius does not specifically comment in his doxography. Bearing in mind both the Stoic conception of 'conflagration' ( ) (see n. 14) and the ensuing clause of the testimony 'which they call "by resolution ( )" ', Posidonius might not have meant by that expression the conflagration exclusively, rather implying the resolution of qualified individuals more broadly. Bernard Collette, however, has suggested (in a Cambridge seminar, 2006) that Posidonius' expression 'an out-and-out change' in Arius' doxography can be regarded as direct evidence for Posidonius admitting the conflagration, a point Kidd (n. 2), 1.387 fails to pick up. However, Kidd's caution may be well placed, on my reading of Posidonius' expression as alluded to above. from body into three: some hold that it is at once dispersed in space, others that it survives a long time, and others that it survives eternally. Within this tripartite grouping Cicero places the Stoics between the Epicureans and Platonists, marking off all three from Dicaearchus who, in Cicero's view, argued most incisively against the soul's immortality. Cicero remarks of the Stoics that they, on the other hand, give us a generous lease of life, as though to make us crows, testifying to a certain scepticism as to whether the soul can indeed survive a long time but not eternally. Conceivably, this Stoic view on perishable souls represented a major stumbling block to Cicero's acceptance of Stoicism, since he himself speaks of it as the point of greatest difficulty in the whole problem.
There seems little reason to deny that mainstream Stoics, or even those contemporary with Cicero, would have been forced to respond to criticism of this kind. Little evidence of the Stoic responses remains, however; and Cicero himself informs us no farther than reporting Panaetius' syllogisms about soul's perishability. 21 But from such evidence as exists we can highlight at least a few aspects of these debates. Consideration of Stoics' debates presented below suggests that a conception of immortal souls is as Stoic as a conception of perishable souls, and further determines Posidonius' fundamental adherence to Stoic orthodoxy on this topic.
In considering the grounds on which mainstream Stoics and Posidonius might have argued for the soul's immortality and perishing, we should particularly remember that no Greek thinkers outside the Stoic school marked off 'immortal' and 'imperishable' from each other with regard either to soul or to god. The Phaedo's final argument, for instance, appears to take 'immortality' to entail imperishability, though these two words are not semantically identical, hereby proving the soul to be both immortal and imperishable. 22 The Stoics are, however, well known for employing 'imperishable' exclusively for their supreme cosmic deity Zeus, at the same time using 'perishable' of the rest of gods and souls as they did of the world. 23 They employed 'immortal', however, for all of these without discrimination, as a range of evidence shows. 24 We can therefore legitimately suppose that the founding fathers of the Stoic school made certain conceptual distinctions between 'immortal' and 'imperishable', inferring, for instance, that the souls are immortal but perishable. This Stoic terminology is exactly what Cicero, and later also Plutarch, 25 seized on to launch one of their strongest 118 A.E. JU 21 Cic. Tusc. 1.79-80. It is uncertain why Cicero argues especially against Panaetius, but perhaps he wanted to show how Panaetius, who revered Plato most among philosophers, neglected the fact that, when Plato spoke of the eternity of souls, this pertained not to the soul's irrational parts, but to the mind which is always distant from disorderly impulse. 22 Pl. Phd. 105e10-107a1; see also Phdr. 245c5-246a2. Plato, at Phd. 106d4-6, applies this combined vocabulary also to 'god' and 'the form of life itself'. Plato's precise position in the Phaedo's final argument on immortality and imperishability is more complex than I indicate, though this does not affect points I have made above. Cf. D. Gallop (ed.), Plato: Phaedo (Oxford, 1988  objections to Stoicism. But it is easy to see this inference as relying both on an originally Platonic definition of death 26 and on a Stoic conception of destruction, in a few regards expanded on below. The Stoics most probably understood 'death' as a form of division, namely 'separation of soul and body', 27 through which any ensouled being loses its own identity. 28 To the extent that they adhered to this definition of the term, they could say that a man dies but a soul or a god does not. That is, according to the Stoics, it is we and not our souls who are subject to death; hence 'we ourselves survive as souls', as Chrysippus says, 'separated from bodies and changed into the lesser substance of the soul', as cited by Eusebius in the passage above. 29 Further, for the Stoics, because the gods are divine, and also because they experience no separation of soul from body, despite being composed of these parts, they are correctly called 'immortal' or 'deathless'. 30 Chrysippus, in Book 1 of On Providence, applied this exact attribute to the world, in asserting that 'the world soul is not separated, but grows continuously until it has completely used up its matter on itself '; hence 'the world must not be said to "die" ' ( ) (Plut. St. rep. 1052c-d). The question arises how far the very focus on immortality in this Stoic material betrays a preoccupation with Platonic concerns as to the soul's immortality advanced in the passages of the Phaedo. It is uncertain whether mainstream Stoics or Posidonius worked with the relevant passages of the dialogue. But the Stoics' conception of the soul's immortality is in no sense a deviation from the language of Platonism, in that they adhered to a Platonic definition of death. Supposing the allegedly Pythagorean origin of the Platonic idea expounded in the passages, it would even seem possible that the Stoics rather wanted to adhere to a core Pythagorean idea of the soul's immortality. 31 Nevertheless, the Stoics' conception of immortal and perishable souls seems to indicate where they diverged from the Phaedo's final argument. It remains conceivable that 'the validity' of this argument 'depends on the condition that the deathless should also be indestructible'. 32 The Stoics, however, may have found this condition implausible, perhaps on the basis of their discrimination between death and the other forms of destruction as previously considered. 33 Since, as noted, for the Stoics 'death' refers narrowly to a form of division (into soul and body) befalling any ensouled being, a soulless thing, for instance an egg, is not said to 'die' in Stoic terms, but is taken by them to be destroyed, whether by mere division (into yolk and white), by fusion (for instance, into a cake), or by resolution (into its components). Further, as indicated, a soul or a god is not said to 'die' either, but is taken to be destroyed by STOIC  In this characterization of the Stoic theory of destruction, Stoicism shows itself capable of defusing all manner of apparent contradictions between the postulates of the soul's immortality and perishing by positing sophisticated distinctions between these terms. There seems little basis for doubting that Posidonius' conception of soul's immortality was genuinely Stoic; and that, in claiming that 'the air is full of immortal souls', he was not deviating from Chrysippus or even from Plato. Bearing in mind Cicero's knowledge of Stoicism in general, we must assume that Cicero in this respect was aware of the Stoic terminology, and rejected it.

II. 'SELF-MOVING SOUL'
We can now profitably turn our attention to Posidonius' interpretation of Phaedrus 245c, as reported in Hermias' testimony (though my examination here will necessarily be glancing). Plato's own lemma reads: […] All soul is immortal; for what is self-moving is immortal; but what is itself moved by something else, imparting motion, ceases its motion, and therefore ceases to live. Only what moves itself never ceases its motion, inasmuch as it cannot abandon itself; moreover, this self-mover is the source and the first principle of motion for all other things that are moved. Now a first principle cannot come into being.
[…] It is as impossible that it should be destroyed as that it should come into being; were it otherwise, the whole heaven and the whole of becoming would collapse, stop, and never again have any other source of motion to bring it back into being.
(Pl. Phdr. 245c5-e3) 34 Hermias states: ' ' 120 A.E. JU We must first ask what kind of soul he [Plato] means. Some thought that his argument referred to the world soul only, because he said 'all' and a little later added that 'were it otherwise, the whole heaven and the whole of becoming would collapse and stop'; the Stoic Posidonius is one of these. Others thought that it referred to absolutely all [soul], including the souls of ants and flies; Harpocration is one of these; he understands 'all' as applying to all soul.
(Herm. In Phdr. ad 245c; fr. 290 EK) 35 A central difficulty in probing Posidonius' equation in Hermias' report of 'all soul' with 'the world soul' lies in the entire lack of context. Even so, from what we know of Posidonius it is not likely that he adopted this equation on the basis of his belief in the immortality of the world soul only. Nor did his reflection centre on the slightly different concept of the world soul as advanced by Plato in the Timaeus; for, as Posidonius presumably knew, the world soul in the Timaeus represents one particular kind of rational soul, alongside other divine souls and the rational part of human souls. 36 Instead, there is reason to believe that Posidonius took account of both the myth and the wider context of the Phaedrus, first because Hermias quotes a relevant section of Plato's argument in introducing Posidonius' interpretation, and second because Posidonius elsewhere himself made use of Plato's figure in the myth of two horses drawn by a charioteer in describing the soul's two irrational parts. 37 Assuming Posidonius' familiarity with the dialogue's context, it remains conceivable that he may not have neglected the fact that Plato's argument for the immortality of soul is meant to be applicable to individual souls, however indirectly. 38 Further, while Hermias insisted that Plato's argument is limited to the soul of god and the rational part of the human soul, 39 Posidonius at least does not seem to have attended to this sort of limitation. Possibly he thought that Plato's focus lies elsewhere; the emphasis in Posidonius' eyes seems to fall much more heavily on the significance of Plato's introducing his argument with the word 'all', as Hermias' report shows. It seems possible, then, that Posidonius inferred 'all soul' to refer for Plato to the whole of soul collectively, including all individual souls. In addition, the principal question in Stoic scholarship on Posidonius' psychology is whether, and if so in what sense, he himself acknowledged there to be parts to the soul; whatever his actual view on the topic, though, this does not seem to have affected his interpretation of 'all soul'.
But, even if this conjecture is correct, the question why Posidonius in his interpretation employed the expression 'the world soul' needs to be answered. Instructively, in Stoic physics, as already noted, the world soul is identical to the whole of soul subsuming all individual souls, whereas individual souls are its parts or offshoots. 40 In this characterization of the Stoic view on soul, it would seem possible that in interpreting 'all soul' Posidonius recruited Plato to the Stoic side; these words become,  Hackforth (n. 34), 64-5 suggests that 'the argument' of the passage 'cannot be regarded as a direct argument for the immortality of individual souls'; but 'it is reasonable to believe -and indeed, since it is the individual soul that Socrates will be concerned with in the myth, we cannot avoid believing -that Plato regarded a demonstration of the immortality of soul in general as applicable to individual souls'. 39 For Hermias' reading of 'all soul' as 'noetic soul', see Robinson (n. 1),111. 40 Cf. n. 10. if taken to refer to the whole of soul, appropriate to the world soul in the Stoic sense. But my preliminary observations tend to suggest that Posidonius' interpretation rather rested on the context in the dialogue, and that by the expression 'the world soul' he meant the whole of soul as understood by Plato.
In pursuing these points further, we can begin by looking at a passage of the myth immediately subsequent to Plato's argument noted above. In the passage, Plato, using the precise words 'all soul', continues: […].
All soul has the care of that which is soulless, and travels the whole universe, coming to be at different times in different forms. So, when it is perfect and winged, it journeys in the upper region, governing the whole world; and when it sheds its wings, it comes to fasten on something solid, and, settling there, takes to itself an earthy body […].  It remains a matter of speculation whether Posidonius referred to the passage of the myth just quoted, since Hermias is silent on the point. But supposing Posidonius did so, the inference would be that he found warrant to believe that 'all soul' represents for Plato the whole of soul, which gives birth to individual souls, as these are in Plato's words 'coming to be at different times in different forms'. Further, this same soul, 'perfect and winged', and in particular in Plato's words 'governing the whole world', is likely to have coincided in Posidonius' estimation with the world soul -as certainly no individual soul can do this -thereby cementing the equation of 'all soul' with the world soul.
In seeking to clarify Posidonius' interpretation further, we can return to the argument of Plato quoted earlier. The question whether in the opening line of the argument Plato used the expression 'what is self-moving' or 'what is eternally moving' has yet to be resolved by scholars. Leaving aside the debate on this crux, what is clear in subsequent lines is that Plato, with a distinction between 'what is self-moving' and 'what is moved by something else', maintains that only what moves itself 'does not cease its motion'. He proceeds to prove this self-mover to be 'the source and the first principle of motion for all other things that are moved', further identifying soul as this self-mover. Plato concludes with the syllogism that what is self-moving is immortal; what is self-moving is soul; therefore soul is immortal.
In speaking thus of soul as the self-mover, Plato offers an interesting disproof of the possibility both 'that it should come into being' and 'that it should be destroyed', on the grounds that the former has already been proved false and the latter is inconceivable. What he takes to be inconceivable is that 'the whole heaven and the whole of becoming', comprising all things that make up any possible universe, should stop and no longer move, for the reason that no source of motion to bring it back into being would exist; but this is inconceivable; therefore, the self-mover cannot be destroyed.
It is likely that Posidonius was specifically engaged by this conditional prediction of Plato's noted above, given that before assigning Posidonius to one group of Plato's interpreters, Hermias explains their interpretation by quoting 'because he [Plato] said "all" and a little later adds that', Were it otherwise, the whole heaven and the whole of becoming would collapse and stop. 41 It seems possible that Hermias here is quoting Posidonius' own citation of this statement from Plato's dialogue. We could, if so, be confident in inferring that Posidonius placed as much weight on the statement as on the word 'all'; and, given that the immediate context of the argument including the statement is Plato's proof of soul as a self-moving substance, it seems possible also to suppose that Posidonius attended particularly to this Platonic conception of soul.
The question immediately arises why Posidonius placed so much weight on Plato's conditional prediction. Posidonius presumably would not quarrel with the syllogism as noted above which stands, even if 'soul' applies to an individual soul, such as Socrates' soul. But in my view, Posidonius judged further that, as far as the conditional prediction is concerned, Plato was treating 'the self-mover' as a term corresponding to 'all soul'. That is, the Platonic conditional prediction in Posidonius' eyes stands if and only if 'the self-mover' carries the same referent as 'all soul' by referring to all the self-moving substance there is. Posidonius' formulation makes sense, in so far as it is clearly possible to go on thinking of the world in the event of the destruction of an individual soul, for instance, Socrates' soul, while, were we to suppose the loss or destruction of all the self-moving substance there is, then we might quite possibly find the motion of the world unimaginable; therefore, this substance cannot be destroyed.
The above discussion has three major suggestions. First, Posidonius did not neglect the fact that Plato's argument is meant to apply to individual souls. Second, Posidonius gave attention to the fact that at the opening of the argument Plato said 'all', further stressing the Platonic conditional prediction that, should the self-mover hypothetically be destroyed, the whole world and the whole of becoming would stop and no longer move. Finally, Posidonius concluded that the truth of Plato's proposition hinged on an identity between 'all soul' and all the self-moving substance there is. It is likely that this conclusion guided Posidonius in inferring that 'all soul' must for Plato refer to soul collectively, taken here as equivalent to 'the soul', in Plato's words, 'governing the whole world'.
Let me conclude with a remark on Posidonius' interpretation of Plato discussed above. It is typical of Posidonius that he read previous philosophers and especially Plato constructively for his own purposes, rarely venturing purely disinterested comments. Taking this characteristic into account, it seems possible that Posidonius used his reading of Plato to support, or at least refine, an essentially Stoic view of self-moving soul. 42 Relevant sources for Posidonius' reflection on Plato's idea of self-moving soul are Achilles Tatius, Intr. in Arat.13 and perhaps also Sextus Empiricus, Math. 9.71-2. 43 Any closer scrutiny of these passages notwithstanding, it seems evident that the passages' sources equally insist, against Epicureanism, on the existence of souls in the extra-terrestrial region, whether these souls be surviving human souls or daemons or the souls of the stars; and that, analogically or otherwise, both bear out a Posidonian idea of the soul's causal action upon itself through its capability of holding itself together. In view of this Posidonian preoccupation, it remains possible that when Posidonius interpreted Phaedrus 245c, his concern lay with the broader context of dealing with the topic of self-moving soul. Possibly, in engaging his contemporaries the Epicureans, Posidonius both had recourse to his Stoic predecessors and solicited the support of Plato by referring to previous conceptions of self-moving soul.
Other material for (perhaps mainstream) Stoic reflection on the Platonic idea of self-moving soul can be found at Sextus,Math. 9.76. 44 Leaving aside the question of Sextus' Stoic source, there seems little room for doubting that the passage's argument represents a standard Stoic doctrine, to which Posidonius seems to have taken no significant exception. The passage itself is roughly reminiscent of the Phaedrus passage that we have been studying, in two basic respects, namely self-motion and eternal motion, despite differences in the detail of the passages' argumentation. From a comparison of the two, it appears that the source of the Sextus passage took over from Plato the distinction between 'what moves itself ' and 'what is moved by something else'. In the first part of the argument, denial of a 'self-moving' power is accused of the absurdity of an infinite regress. The author proceeds to prove this self-moving power to be 'divine and everlasting', maintaining the impossibility of its being in motion 'from some point in time', as there could then be 'no cause of its motion'; therefore it must 'be in motion from eternity'. The general ideas of the argument and in particular the term 'self-moving' are strong confirmation that the Stoics' conception of such a self-moving power, taken here as equivalent to 'god' or Stoic 'reason', echoed the Phaedrus passage discussed above even when they were not interpreting it directly. 45

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A.E. JU julepli@hotmail.com 124 A.E. JU the basis that, although the Sextus passage does not refer to Posidonius by name, it would seem baseless to deny its similarity with the Achilles passage, both doctrinally and in textual features. But, for lack of direct evidence, it appears difficult to determine that the subsequent section of Sextus, Math. 9.73-6 derives from a Posidonian exposition. However, the arguments of this section seem to represent standard Stoic doctrines, to which Posidonius seems to have taken no significant exception. 44 Cicero, at Tusc. 1.53-5, discussing previous philosophers' views on the immortality of soul, quotes the same argument of the Phaedrus to which Posidonius referred, except for the opening sentence . Cicero possibly knew Posidonius' interpretation of the argument. Judging from Cicero's translation of as quod semper movetur aeternum est (1.53), and his accompanying comment (1.55), he favoured . Sextus, Math. 9.76, on the other hand, tends to suggest that Sextus' Stoic source employed . It seems possible that Cicero differed from the Stoics in interpreting Phdr. 245c-e; yet it is unclear whether their difference was associated with the competing positions of the Stoic and Academic schools over this crux. 45 This article has benefited from discussion with Christopher Gill, Alexander Mourelatos, Terumasa Ohkusa, Malcolm Schofield, David Sedley, Stephen White and Hoyoung Yang. I thank the editors and anonymous referee of CQ for suggestions and corrections.