Abstract
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Pores and Void in Asclepiades’ Physical Theory
Abstract
This paper examines a fundamental, though relatively understudied, aspect of the physical theory of the physician Asclepiades of Bithynia, namely his doctrine of pores. My principal thesis is that this doctrine is dependent on a conception of void taken directly from Epicurean physics. The paper falls into two parts: the first half addresses the evidence for the presence of void in Asclepiades’ theory, and concludes that his conception of void was basically that of Epicurus; the second half focuses on the precise nature of Asclepiadean pores, and seeks to show that they represent void interstices between the primary particles of matter which are the constituents of the human body, and are thus exactly analogous to the void interstices between atoms within solid objects in Epicurus’ theory.
In memory of Bob Sharples
The physiological theory of Asclepiades of Bithynia (fl. later second/earlier first century BC) stated that the human body, like all perceptible objects, is composed of imperceptible particles referred to as onkoi. Health is maintained by the free and balanced motion of these onkoi through imperceptible pores in the body, while disease results from blockages and rebounds arising ultimately from the differences in the sizes and shapes of both the onkoi and the pores. Explanations of a full range of physiological and psychological processes were also derived from the postulated existence of these pores and the movements of the onkoi through them. It is also clear that these ideas formed part of a fully worked-out physical system which is of considerable interest in its own right. But while the nature of Asclepiades’ onkoi has received a fair amount of attention, the same cannot be said for his pores. What precisely did they represent?
Galen, our most explicit source on their basic nature, informs us that they were equivalent to Epicurean void spaces. A number of scholars who have been happy to accept the influence of Epicurus in this regard accept with little comment that Asclepiades posited large-scale void.1 Others, in particular those who deny Epicurean influence, have simply ignored the question of void within Asclepiades’ theory.2 But Galen’s testimony has also been openly called into question, and the most recent study, that of John Vallance, who was the first to give this issue the attention it deserves, has framed the question of the nature of the pores in terms of whether or not they represented void (and if so, what kind).3 Vallance himself did not reach any firm conclusions, but offered a range of possible lines of inquiry.
The nature of the pores and the question of void in Asclepiades’ theory thus remain points of controversy, though these issues are clearly fundamental to our understanding of his theory and its intellectual background. The present paper attempts to resolve at least some of the controversies surrounding Asclepiadean pores and to offer a detailed account of their basic character.4 In section I, I shall consider the evidence for the general thesis that Asclepiades was a void theorist, and in section II, the evidence for the nature of Asclepiades’ pores in particular. I shall argue that the relevant sources point unmistakably to Epicureanism as the source of Asclepiades’ doctrine both on void and on the pores. Although this general conclusion has been accepted by some, it has not received the full defence it requires. This is of obvious significance for the broader influence and reception of Epicureanism in the late Hellenistic period, and offers a striking example of the ways in which medical thinkers adopted and reworked contemporary philosophical theories.
I Void
An analysis of Asclepiades’ position on void must begin with Galen, who is the only ancient authority to offer explicit testimony on the subject. There are a number of directly relevant passages:
Asclepiades recognized none of these (sc. structures at the base of the heart in the embryo), and even if he had, it would have been impossible for him to discover their causes, since he refers the origins of everything which comes to be to onkoi and void.
UP 6.13 [3.474 K. = p. 346.8-11 Helmreich]
That there are certain void spaces in both water and air follows from the doctrine of Epicurus and Asclepiades on the elements.
Hipp. Epid. [17B.162 K. = p. 215.3-5 Wenkebach]
By ‘rarefied’ (substance) I mean that which has parts which are separated by empty spaces, understanding of course and recalling always the way in which ‘empty space’ is meant by those who say that substance is continuous, (i.e.) that in all rarefied bodies ‘empty space’ is not as Epicurus and Asclepiades think, but full of air.
SMT 1.14 [11.405 K.]
For if everything is constituted out of atom and void according to the theory of Epicurus and Democritus, or out of certain onkoi and pores according to the physician Asclepiades – for in this way he changed only the names, speaking of onkoi instead of atoms, and pores instead of void, and wanting the substance of what exists to be the same as they (did).
Ther. Pis. 11 [14.250 K.]
Galen here offers unambiguous testimony, repeated in a range of contexts, that Asclepiades was a void theorist, and adhered to a specifically Epicurean conception of void. As noted above, this testimony has been called into doubt. Certainly, given his tendentiousness in reporting or interpreting the views of his predecessors, doctrinal friends and enemies alike, Galen’s claims must generally be treated with caution.5 But he is not to be dismissed out of hand, and there are two points which I would emphasize regarding his specific testimony before discussing the arguments which have been raised against it.
Firstly, Galen’s close familiarity with the details of Asclepiades’ element theory cannot be doubted. The fact that Asclepiades wrote a treatise entitled On Elements is known only from him.6 In On My Own Books, Galen tells us that a comprehensive demonstration of his own doctrine on elements was to be found in two places, both now lost, namely book 13 of his monumental On Demonstration and books 5 and 6 of his 8-book work On the Opinions of Asclepiades.7 It seems safe to assume that the latter demonstration was located within, and formed part of, a detailed refutation of Asclepiades’ own element theory.8 Secondly, Galen would not appear to gain much by falsely attributing a theory of void to Asclepiades. He is uniformly hostile to Asclepiades, but nowhere openly seeks to refute him on the grounds that he was a void theorist, notwithstanding his own rejection of the void. Nor does he attack Epicurus on these grounds either. Rather, the charges most often levelled against them are the inability of their theories to account for qualitative change, their rejection of teleology, their denial of Galen’s conception of natural faculties, or their failure to account properly for cognitive processes. For each of these charges, there is plenty of independent evidence that Asclepiades had indeed adopted the position that Galen tells us he had. On the other hand, Galen often presents as an opponent’s doctrine what in fact turns out to be nothing more than what Galen regards, based on his own principles, as the logical consequence of his opponent’s doctrine. The consequence is drawn out in order to show its manifest conflict with the opponent’s principles or with the phenomena. Ascribing a theory of void to Asclepiades (and to Epicurus) does not fulfil this function: Asclepiades’ postulation of void is nowhere said to be in conflict with the phenomena, and is said to be consequent on his own principles.
The main proponent of a sceptical attitude towards Galen’s testimony is Vallance. Based on the divisibility of the onkoi and the indivisibility of atoms, Vallance denies any Epicurean influence on Asclepiades’ theory of matter. If this were correct, it would obviously undermine Galen’s testimony on Asclepiades as a void theorist. I have tried to show elsewhere, however, that Asclepiades’ conception of his onkoi is indeed based directly on Epicurean atomism, and that the differences between the two can and should be explained as a conscious modification on Asclepiades’ part.9 On this interpretation, Galen’s comments on Asclepiades’ theory of matter are justifiable, if somewhat misleading, and his claim that Asclepiades also took over Epicurean void becomes all the more credible.
However this may be, Vallance attempts to cast specific doubts on Galen’s claim with his assertion that in the contexts in which Galen associates Asclepiades with Epicurean void, his anti-Methodist polemic is in fact somehow in the background.10 This is simply not true, however, of any of the passages quoted above in which Galen explicitly characterizes Asclepiades as a void theorist: there is no indication in the contexts in which they are found that the Methodists are on Galen’s mind. Vallance goes on to claim that ‘Galen argues that the Methodists actually shared the Asclepiadean doctrine on void.’ His point is apparently that, since it is highly doubtful that the Methodists themselves held a doctrine of void, we should not take Galen’s attribution of such a doctrine to Asclepiades at face value either, and he suggests that ‘Galen has more on his mind than he explicitly admits to.’11 The passage which Vallance adduces to show that Galen made the Methodists out to be void theorists, however, does not support his claim. He cites the beginning of On the Causes of Diseases,12 which distinguishes between those who think that substance is continuous and undergoes alteration in coming to be and passing away, and those who think that it is not continuous but that every compound is interwoven with void. Vallance asserts that, as it emerges later in the treatise,13 the latter group turn out to be Methodists. In fact the Methodists are not mentioned anywhere in On the Causes of Diseases, either individually or collectively. In the passage that Vallance cites, the only sentence that isolates any particular group is Galen’s reference to those ‘who think that (sc. the homoiomerous parts) are composed of onkoi and pores,’ but it is question-begging to identify these people as Methodists, and I see no reason not to identify them simply as Asclepiadeans.
Indeed, Galen elsewhere can be quite clear about the Methodists’ views on void. In his Method of Healing, he argues that their use of certain kinds of terms commits them to a theory of matter similar to that of Asclepiades, since the use of such terms ‘is legitimate only for those who posit onkoi and pores or atoms and void or generally impassive and unalterable first elements.’14 He is certainly not thereby asserting that the Methodists were void theorists, but merely that, given the provenance of the sorts of terminology they use, they ought to be. The Methodists, with regard to therapeutic practice at least, rejected Dogmatist theorizing about hidden matters as irrelevant. Galen thus argues that their self-proclaimed emancipation from Dogmatist theorizing about hidden matters is fundamentally inconsistent with the fact that the concepts they employ presuppose it. This accusation only makes sense if Galen believed (or at least wanted his readers to believe) that the Methodists as a group did not consider themselves committed to a doctrine of onkoi, pores, void, or any such hypothesis derived from speculation on non-evident matters. All this is in marked contrast to Galen’s direct and unqualified characterization of Asclepiades as a void theorist. Galen’s statements on the Methodists’ rejection of such speculative theories as the basis for therapeutics receive ample confirmation elsewhere, and therefore they cannot be used to call into question his association of Asclepiades with Epicurean void.
Vallance also expresses puzzlement at the fact that none of our other sources which discuss Asclepiades’ doctrine of pores explicitly mention that they represent void.15 I shall argue in the next section that we are simply not entitled to expect our sources to do so, and that an underlying concept of void is already implicit in the language they use to describe the pores. Despite these reservations, however, Vallance concedes in the conclusion to his chapter that the onkoi move about ‘in what may after all have been an Epicurean void,’ and that ‘[i]t is not necessary to reject Galen’s testimony about Asclepiades and the void.’16
All the same, we shall only accept Galen’s testimony with confidence if it is not contradicted by other sources, and if it is in turn supported by them. The first of these conditions can be quickly dealt with, for there is nothing to my knowledge in the extant sources which would conflict with Galen. There is, on the other hand, corroborating evidence of various kinds for Galen’s assertion that Asclepiades was a void theorist in the Epicurean mould.
Firstly, Calcidius provides the following generalizing account of a number of thinkers who oppose Plato’s doctrine on the seat of the ruling-part-of-the-soul:
qui dividuam fore silvae substantiam censuerunt interponentes immenso inani modo expertia modo partes quidem, sed indifferentes, sui similes, tum atomos vel solidas moles, nullum locum certum definitumque principali animae parti dederunt.
Those who have thought that the substance of matter is discontinuous,17 interspersing in the immense void now partless bodies, now things which are parts, but undifferentiated and similar to themselves, now atoms or solid masses, have assigned no definite or circumscribed location to the ruling-part-of-the-soul.
Calc. In Tim. 214
It has been shown that Calcidius is drawing here ultimately on the Placita tradition, and that the parallels with other sources indicate clearly that the authorities referred to in this chapter are, in order, Diodorus Cronus (with his partless bodies), Anaxagoras (homoiomeries), Epicurus and Democritus (atoms), and finally Asclepiades (Calcidius’ solidae moles rendering 
).18 That Asclepiades is meant is further confirmed by the fact that the moles are explicitly linked to him by Calcidius a few lines later.19 Hence Asclepiades is listed among those who posit large-scale void. Immediately, however, the fact that Anaxagoras is also numbered among the void theorists, where he certainly does not belong, undermines the reliability of this testimony for Asclepiades, and a case could accordingly be made for a more general doxographical distortion in this passage. On the other hand, things are not quite so simple with regard to Asclepiades, for the passage is inaccurate in another respect, in that the principal point of doctrine which Calcidius attributes to all these authorities in this sentence, viz. the non-existence of a localised ruling-part-of-the-soul, is one which is only attributable to Asclepiades. It has been persuasively argued that the doctrine described here by Calcidius is in fact based primarily on Asclepiades’ theory.20 Therefore, if there is any truth to the attribution of void to these authorities, then we would expect it to be true of Asclepiades most of all. And of course we know that it is not entirely inaccurate, since the attribution is at least true of Democritus and Epicurus. Calcidius’ testimony thus offers some degree of support for Asclepiades as a void theorist, though by itself it is certainly open to suspicion.
Further support is provided by two sources which each state that Asclepiades regarded both the onkoi and the pores independently as elements:
According to Asclepiades the elements of man are frangible onkoi and pores.
ps.-Gal. Int. [14.698 K. = p. 21.12-14 Petit]
In the third sense, hypothesis means the basis of a proof, that is, a postulate for establishing something. In this sense it is said that Democritus uses as a hypothesis atoms and void, and Asclepiades onkoi and pores.
ps.-Hero, Def. 138.8 [p. 166 Heiberg]
The ps.-Galenic author of the Introductio sive Medicus explicitly states that there are two irreducible constituents of the human body, the frangible onkoi and the pores.21 Insofar as they are both elements, these entities are presented as sharing the same ontological status. In ps.-Hero,22 the parallelism invoked between Democritean atoms and void and Asclepiadean onkoi and pores clearly also suggests that there is the same ontological parity between the latter pair as between the former.23 The author does not identify the onkoi with atoms, nor the pores with void, but there is an implicit acknowledgement that both pairs have an analogous and co-ordinate relationship in both theories. We know that the onkoi were the ultimate constituents of all bodies, and the fact that the pores were not ontologically posterior to them would most obviously point to their representing void, that is, not-body. Although these testimonia do not entail that Asclepiades’ pores represented Epicurean-style void, that supposition would make excellent sense of their evidence.
It is also important that Asclepiades’ onkoi are in perpetual motion.24 For in the Epicurean system, the perpetual motion of the atoms is entailed by the existence of void, because of its absolute non-resistance.25 In this, as in other aspects of his theory, Epicurus seems to have been influenced by Aristotelian criticisms of void. In Physics 4, Aristotle had argued that if something in a void was in motion, then there could be nothing which could make it stop: ‘it will either be at rest, or necessarily carry on to infinity, unless something stronger impedes it.’26 Epicurus appears simply to have accepted this argument, and concluded that indeed the atoms were in perpetual motion.27 Thus both Aristotle and Epicurus affirm that perpetual motion is entailed by void. While it is conceivable that Asclepiades inferred the perpetual motion of his onkoi on the basis of some other hypothesis, it is difficult to imagine what this might have been,28 and the most economical explanation is, again, that he also posited Epicurean-style void.
There is, however, another piece of evidence, in this case derived from Asclepiades’ own argumentation, which offers additional confirmation of his postulation of void. The Anonymus Londinensis records a number of Asclepiades’ arguments for the existence of invisible pores in the body, one of which is in fact identifiable as an argument used by both the early atomists and the Epicureans to establish the existence of void. This is the argument derived from the phenomenon of growth.29 I offer here a revised text based on autopsy of the papyrus:30
Since, says [sc. Asclepiades], every part of our body is nourished and, for the sake of argument, body does not pass through body, both the whole and the individual parts of the body grow by means of nourishment permeating it and passing to every part of the body through the existence of pores perceptible to reason.
Anon. Lond. xxxix 10-15
Again in Physics 4, Aristotle attributes a number of arguments for void to the early atomists, of which the third is also based on the phenomenon of growth:31
Next, everyone thinks that growth happens through void. For nourishment is a body, and it is impossible for two bodies to be in the same place.
Phys. 4.6, 213b 18-20
Although there is little obvious textual correspondence between these two versions, the analyses of the argument by Themistius and Simplicius in their commentaries on the passage bring out the formal parallelism clearly:
It is clear furthermore that growth cannot exist without the existence of void. For it is necessary that growth occurs by the assimilation of nutriment everywhere in the body which is being increased, and this would not happen if it was not dispersed everywhere. But it is impossible for it, being body, to pass through the whole body, unless we place some void in bodies.
Them. Phys. 124.4-9
If growth happens through the dispersal of nutriment everywhere, and nutriment is body, it must happen through a plenum or through void. But through a plenum is impossible, as has been shown (for body does not pass through body, such that there are two bodies in one place). It is clear therefore that the entry of the nutriment into void spaces in the nourished body which are spread everywhere causes the nourished body to grow in every part.
Simpl. In Phys. 651.2-8
Both Asclepiades’ argument and that reported by Themistius and Simplicius infer from the uniform growth of animals that nutriment is distributed to every part of the body. A disjunction is then introduced, such that the distribution of the corporeal nutriment must occur either through space that is full or space that is empty. The principle that ‘body does not pass through body’ is used to exclude the first alternative, leaving the second as the necessary conclusion. That the same argument was used by the Epicureans as a proof of void is indicated by a brief reference to one of its premises made by Lucretius at 1.350, among his arguments for the existence of void: ‘dissipat in corpus sese cibus omne animantum’ (‘Food is distributed through the whole body in living creatures’).32
Asclepiades’ version is paralleled so closely by the argument described by Themistius and Simplicius that it is difficult to escape the conclusion that he knew at least an earlier version of it. His use of an atomist argument for the existence of void, then, clearly points to his acceptance of the same conclusion. Although the Peripatetics could also rely on the principle ‘body does not pass through body’ in explaining growth with reference to their refutation of the Stoic theory of total blending (
),33 they did not operate with the disjunction which Asclepiades presents. Rather, they argued for a third possibility as an explanation for growth, that organic matter is simply displaced, based ultimately on their theory of 
or ‘reciprocal replacement,’ and deployed other arguments to rule out the atomists’ conclusion. Asclepiades’ recognition of only two possibilities thus places him firmly in the camp of the void theorists.
Asclepiades, nevertheless, does not mention the existence of void in his own version, but only the existence of invisible pores. I suggest, however, that this apparent difference need only be one of emphasis, for this argument from growth will yield not only void per se, but in particular void within a living body, and thus void in the form of gaps between primary particles in a perceptible, solid object, allowing the movement of matter to every part of the body as a whole. This, certainly, is what is envisaged in the Epicurean theory of the distribution of nutriment. As I shall argue in section II, this is also exactly what Asclepiades’ pores were. While the atomists used this argument in order to establish the existence of void within the universe, Asclepiades was interested primarily in the physiology of the living body, to which his theory of pores was central, and so naturally emphasised that conclusion which was germane to his purposes.
Some further points of interest are raised by Asclepiades’ use of the principle ‘body does not pass through body.’ Robert Todd has argued convincingly that the discrepancy between Aristotle’s phrase ‘it is impossible for two bodies to be in the same place’ and the commentators’ ‘body does not pass through body’ reflects the reformulation of the general argument to suit the new context of a refutation of the Stoic theory of total blending, which was taken by their opponents to entail that ‘body passes through body.’34 Certainly the form ‘body does not pass through body’ is nowhere used by Aristotle, and it seems safe to assume that it post-dates him. In fact, it is Asclepiades himself who is the earliest documented thinker to have adduced it,35 though we should assume that he was not the first to formulate it as such. Interestingly, as we are informed by Galen, Asclepiades himself attacked the Stoic theory of total blending in his treatise On Elements, and, according to an anonymous scholiast on the Galenic passage, in that context too used the principle ‘body does not pass through body.’36 Todd argues that the reformulation and its anti-Stoic use originated within the Peripatetic exegetical tradition.37 I would suggest, however, that an Epicurean origin for the principle ‘body does not pass through body’ is much more likely. It is only for the Epicureans (i.e. insofar as the Epicureans are the only, or at least most prominent, post-Aristotelian void theorists) that a constructive use of the principle can be found, viz. in the argument for void from growth reported by Themistius and Simplicius and referred to by Lucretius. It is not implausible on historical grounds to imagine that they would have had an interest also in its destructive function in the refutation of the Stoic theory of total blending, though no extant source, as far as I know, explicitly attributes such an argument to them. Moreover, as I am arguing in this paper, Asclepiades’ argument from growth employing the principle is more likely to have been taken over from the Epicureans. It is therefore most economical to assume that he also inherited from the Epicureans at least that part of his refutation of Stoic total blending which rested on the principle, and that they were in fact the first to formulate it as ‘body does not pass through body.’
Galen’s unambiguous and informed testimony that Asclepiades was a void theorist in the Epicurean vein is thus corroborated implicitly by Calcidius, and indirectly by two further independent sources. That Asclepiades posited void is also presupposed by his use of an atomist argument for the existence of void, and by the fact that another aspect of his theory of matter, viz. the perpetual motion of the onkoi, which is only precisely paralleled in Epicurean physics, is conceptually dependent on the existence of void according to both Epicurus and Aristotle. The next section will be devoted to an analysis of the nature of Asclepiades’ pores, and I shall argue that not only is this consistent with their signifying void, but also that Asclepiades’ conception of them coincides exactly with the Epicurean theory of void interstices.
II The Pores
The fullest description of the pores is provided by Caelius Aurelianus:
fieri etiam vias ex complexione corpusculorum intellectu sensas, magnitudine atque schemate differentes, per quas sucorum ductus solito meatu percurrens si nullo fuerit impedimento retentus, sanitas maneat, impeditus vero statione corpusculorum morbos efficiat.
From the combination of the onkoi, pores intelligible to reason also come to be, which differ in size and shape. As the passage of liquids goes through these with its usual motion, if it is not impeded by any obstacle, health persists, but when impeded by an obstruction of the onkoi it produces diseases.
Cel. Pass. 1.14.106 [p. 82 Bendz]
This account is largely confirmed by Sextus Empiricus, though he does not specify that the pores differ also in shape:
In this way we say that Asclepiades used three hypotheses for establishing the obstruction which produces fever: the first, that there are certain theoretical pores in us, differing from each other in size; …
S.E. M 3.5 [pp. 107-8 Mau-Janacek]
Like the onkoi, the pores fall below the level of sense perception, and their existence has to be inferred with the use of reason, that is, they are intellectu sensae, or in Greek 
(
in Sextus). Also like the onkoi, they differ from each other in size and shape. It will also be noted that the human body is the focus in both accounts.
The main issue for our purposes is what precise relationship the pores have to the onkoi, and what exactly Caelius’ complexio corpusculorum refers to in the above passage. Vallance interprets Caelius as affirming the ontological priority of the onkoi over that of the pores, presumably in the sense that the pores are constructed out of onkoi, just as all perceptible objects are.38 This interpretation is of course inconsistent with Galen’s testimony that the pores represent void, and with the statement of the ps.-Galenic author of the Introductio sive Medicus cited above, which clearly implies the ontological parity of the pores with the onkoi. For independent reasons, however, I maintain that Caelius’ testimony should be interpreted along the lines of the Galenic and ps.-Galenic testimonia.
The question can perhaps be formulated more clearly by examining the ambiguity inherent in the term 
itself. As Lonie well brought out in a related study, 
is used by a variety of medical and philosophical writers to characterize any or all of the vessels or channels found within the body, whether blood-vessels, the optic nerve, the spermatic ducts, etc.39 But Lonie isolates a different usage, of which he finds examples first in the ps.-Aristotelian Problemata, referring not ‘to the normal channels of the body,’ but ‘to the interstices of bodily substances which are regarded as porous.’ Although Lonie sees the origins of this latter usage in the Stratonic conception of discontinuous void, there is no reason to consider its general sense theory-specific.40 One might broadly typify the first usage as emphasizing the physical object or structure through which matter may travel, but the second as implying primarily the mere absence of a physical obstacle to the passage of matter. Modern analyses of Asclepiades’ doctrine of pores sometimes translate 
in ways which seem to presuppose the former usage, for example with terms such as ‘canaux,’41 or ‘canali.’42 But we must be clear about what sorts of assumptions such translations involve, and how our interpretations of the evidence are conditioned by them. If, of course, one thinks of a 
as a channel or vessel, and thus as a physical structure in the former sense, then one is likely to read Caelius’ description of the pores arising from the combination of the onkoi as referring to the ontological priority of the onkoi over the pores, with the latter being composed of the former. But if one thinks of a 
as a gap or interstice, simply allowing the passage of matter through it, then this is emphatically not so: there would be no grounds for thinking that Caelius meant that the pores were reducible into onkoi as into their constituent parts. There are various kinds of evidence showing that Asclepiades can only have intended the latter meaning when he used the term 
, and that the pores represent gaps or interstices between the onkoi when in combination, allowing their movement between each other.
Firstly, 
is only one of two terms which are used by our sources to describe Asclepiades’ pores. The other is 
.43
is the more frequent in the Asclepiadean testimonia, and is used exclusively by such authors as the Anonymus Londinensis in this context. Galen uses the term 
on only three occasions in his entire corpus, on two of which it certainly refers to Asclepiades’ theory.44
is also used by Sextus Empiricus, who wrote on Asclepiades’ doctrine,45 and by the ps.-Galenic author of the Introductio sive Medicus.46 We may note, too, that 
and 
are neatly paralleled by the only two attested Latin terms for Asclepiades’ pores, namely viae and foramina.47
, of course, cannot mean ‘channel’ or ‘vessel,’ etc., or refer to a physical structure of this sort, but it certainly can, or rather does, mean ‘gap’ or ‘interstice.’ Our understanding of the pores should thus be informed by the meaning of both terms used to describe them: 
effectively rules out the former usage of 
described above, viz. as ‘channel,’ whereas it coincides precisely with the latter, viz. as ‘gap.’
Additionally, Epicurus used the term 
in essentially the same way as I am suggesting it was used by Asclepiades. At Letter to Herodotus 61, for example, in arguing that the atoms must move with equal speed when travelling through void, whether they are heavy or light, Epicurus uses several locutions to describe the fact that nothing gets in their way, one of which is 
(‘having every route commensurate with them’).48 Likewise at Letter to Herodotus 47, he asserts that, because of the extreme fineness of the eidola emitted from objects, these also move at an unsurpassable speed: their fineness means that, again, they have 
.49 He is not suggesting that the eidola have a specially conforming channel or duct through which they pass, but merely that, given their size, they have free passage, without physical obstacle. These passages or routes clearly refer to the free passage of atoms through void, but the same concept of free passage is at work in his description of fine water passing through suitably sized 
in the clouds in the production of snow at Letter to Pythocles 107.50 The idea behind his use of 
is consistently that of an area containing no physical obstacle to the passage of an object. This is precisely the underlying meaning that I would assign to Asclepiades’ use of the term in his own physiological system.
We may also consider Caelius’ testimony that the nature of Asclepiades’ pores is such that the human body is completely permeable, and that there is no part of it which is not connected to every other:
ipse denique accusans utentes ait continuationem clysterum incendium atque sitim facere. inusta enim intestina melle atque ceterarum specierum mordicatione movent fervorem plurimum, qui per alta quadam continuitate viarum membranae cerebri influat. cuncta etenim, inquit, quae sunt in alto corporis constituta, sese occulta vicinitate contingunt, quorum in numero membranam cerebri ponimus.
[Asclepiades] himself, in attacking those who use (sc. this treatment), says that the continuous use of clysters produces burning and thirst. For the intestines when heated by honey and by irritation of other kinds produce a great amount of heat which flows through the inner parts by a certain continuity with the pores of the membrane of the brain. For all things, he says, which are situated in the interior parts of the body are in contact with each other by a hidden connection, and we count the membrane of the brain among these parts.
Cel. Pass. 1.15.128, p. 94 Bendz
This ubiquitous permeability clearly describes the complete porosity of the human body, in a way which is prima facie much more suggestive of a conception of the pores as gaps between onkoi, rather than their conception as channels or vessels, which would seem to imply that some parts were interconnected as others were not (so at least is the basic notion when one thinks of visible channels, for example blood vessels or nerves). The opportunities for passage are everywhere, and everything is interconnected.
In this way, then, Caelius’ complexio corpusculorum, from which the pores arise, will refer simply to any complex or composite of onkoi, in which the pores are merely the gaps or interstices delimited by at least two onkoi, allowing other onkoi to pass between. There is no need to import into Caelius’ use of the term complexio anything more complicated, such as the arrangement of the onkoi into particular conformations, for example those of channels or vessels. All bodies for Asclepiades, of course, are made up of aggregates of onkoi, as Caelius tells us in the immediately preceding passage (1.14.105, where the corpuscula ‘adiecta vel coniuncta omnia faciant sensibilia’), and complexio here should simply be a generic term for their combination.51 Relevant Epicurean parallels can be adduced for complexio as well. Cicero, whom Caelius used to some extent as a model for his translation of Greek terms,52 likewise uses the term to describe generally the way in which atoms combine to form all complex bodies.53 Given this interpretation, we can also better understand how the differences in size and shape of the pores come about. There is an exact parallelism between Caelius’ descriptions of the pores and the onkoi. At On Acute Diseases 1.14.105 and 106 respectively, he describes the corpuscula as ‘magnitudine atque schemate differentia,’ the viae likewise as ‘magnitudine atque schemate differentes.’ The precise repetition of this description within a few lines, and the fact that the pores result from the combination of the corpuscles, could be taken to imply that the differences in size and shape of the pores are derived, at least in part, from those of the corpuscles. Thus the shape and size of the gap delimited by a group of onkoi would be directly determined by the shapes of those onkoi, since their surfaces will partially define the outer limits of the gap itself.
Accordingly, the Asclepiadean pore is an imperceptible gap or opening between onkoi within the solid structure of the human body through which other onkoi may pass. These gaps vary in shape and size depending on the shape and size of the delimiting onkoi. We may also assume that temporal variation in the size and shape of the pores is caused by the fact that the onkoi are in perpetual motion. If this interpretation is correct, then it can also be shown that these features of Asclepiades’ pores are precisely paralleled by the Epicurean doctrine of void gaps between atoms within solid structures.
It is of course a central tenet of atomism that the atoms of which all perceptible objects are composed are separated from each other by void. This entails that all apparently solid objects in the visible realm are in fact permeable. At a general level in his explication of Epicurean physics, empirical observation of the permeability of apparently solid forms of matter constitutes part of one of Lucretius’ arguments for the existence of void.54 At a more specific level, on the other hand, when Lucretius turns to his explanation of the physical processes associated with animate beings, and indeed with pseudo-animate objects such as the magnet, the doctrine of void comes to be expressed in terms of pores, gaps or interstices, as indeed we would expect in the context of confined areas of void within a solid object. With reference to Asclepiades, we may note firstly that Lucretius uses the same terminology as we find applied by Celsus and Caelius respectively to Asclepiadean pores, viz. foramina and viae,55 but it is in the specifics of the theory that the more suggestive parallels can be identified.56 The existence of openings or interstices in solid objects, as we have seen, is a consequence of the intervals of void which must exist between individual atoms. In the context of his explanation of how various living things have differing tastes, Lucretius comes to analyse the relationship between the interstices and atoms more fully:
semina cum porro distent, differre necessest intervalla viasque, foramina quae perhibemus, 650 omnibus in membris et in ore ipsoque palato. esse minora igitur quaedam maioraque debent, esse triquetra aliis, <aliis> quadrata necessest, multa rotunda, modis multis multangula quaedam. namque figurarum ratio ut motusque reposcunt, 655 proinde foraminibus debent differre figurae, et variare viae proinde ac textura coercet. Since further the seeds differ, the intervals and passages, which we call openings, must also differ throughout the frame and so also in mouth and palate. Some therefore must be smaller and some larger, some triangular and some square, many round, some again with many angles in many arrangements. For as the relation of shapes and as the motions demand, so the shapes of the openings must differ, and so the passages must vary as the texture compels.
Lucr. 4.649-57, trans. Smith, Loeb, with slight changes
Lucretius’ account is here coloured to a certain extent by his immediate concern to account for differing experiences of flavour in different animals, but it is clear that the theory of the pores it describes is of general application. We see here that the interstices are characterized by differences in their size and shape, and that these differences are derived simply from the variations in the sizes and shapes of the atoms which delimit them.57
In its basic features, then, this account precisely parallels the descriptions of Asclepiades’ pores: in both theories, primary particles in perpetual motion, when they come together to form solid, perceptible objects, nevertheless have empty gaps or interstices between them which differ in their size and shape depending on the shapes and sizes of the confining particles. These interstices also allow the passage of primary particles through them. Given these precise and comprehensive parallels between the two theories, including the corresponding Epicurean and Asclepiadean usage of the term 
, and since Epicurean interstices represent void, it is very difficult to avoid the conclusion not only that Asclepiades’ pores likewise represent a similar conception of void, but also that his theory of pores is basically derived from Epicureanism.58 This is exactly what Galen repeatedly tells us, and we have seen that nothing in the ancient sources contradicts his attribution of Epicurean-style void to Asclepiades, while several testimonia independently corroborate it. This conclusion is also entirely in keeping with the supposition that, as I have argued elsewhere, Asclepiades’ onkoi were in all significant respects, save their divisibility, fundamentally like Epicurean atoms, and even where they differ from atoms, there is evidence that Asclepiades was consciously innovating on the underlying atomistic system.59
An answer can also be given to the question why the sources consistently refer to the pores in discussing his theory, rather than void per se, despite the fact that void must have been what they represent. I suggest that, in the principally medical contexts with which our sources are concerned, Asclepiades was for the most part simply not interested in void per se, but only in void as manifested within the human body. This is well illustrated by the purpose for which he uses the atomists’ argument from growth as discussed above. We have no evidence that Asclepiades was concerned with wider cosmological issues in his theory; his primary focus was the nature of man, not the nature of the universe. While Asclepiades’ theory entailed that there were certain void spaces within any solid structure, and so a fortiori within the human body, his interests lay in their potential to explain a range of physiological and pathological processes, in particular to explain the movement of matter within the body. It was thus principally the functional aspect of void spaces as pores allowing the movement of onkoi that concerned him, rather than their physical or ontological status. Even if most of our sources do not make the specific point that Asclepiades’ pores were void pores, there is little reason to suppose that Asclepiades had cause to make this point except in a detailed and basic account of his elements, and in this context he may well have spoken of void per se (
). His work On Elements obviously suggests itself as a plausible home for a prolonged discussion of the pores, and we may speculate that Asclepiades discussed their void nature explicitly there. Galen had certainly read this work, and it is perhaps not entirely a coincidence that the only ancient source who states explicitly that Asclepiades adhered to an Epicurean conception of void is also the only one whom we know to have read his treatise On Elements.
As a brief epilogue, some comment may be thought necessary on the possibility that Asclepiades instead posited a form of Stratonic disseminate microvoid.60 The ancient sources, it will be noted firstly, point to no such link. The idea rests on the assumptions firstly that Asclepiades’ theories were derived in some way from Erasistratus’ principle of ‘the following (of matter) towards the area being vacated’ (
, PTKA),61 and secondly that this in turn was based on Strato’s theory of matter. In my view, neither assumption can be substantiated. Concerning the latter, while Erasistratus shows knowledge of what appears to be the Stratonic distinction between large-scale void and disseminate void, it seems clear that he thought the principle of PTKA to be connected only with the impossibility of the existence of large-scale void, and that he did not therefore feel the need to pronounce definitely on the existence or non-existence of the disseminate kind.62 Nor is there explicit evidence that Strato himself adhered to a principle similar to PTKA, and even if he had, this would certainly not have been conceptually dependent on a theory of microvoid.63 If there is no reason to associate Erasistratus and PTKA with microvoid, then there is no reason to link Asclepiades with microvoid either. But the evidence linking Asclepiades’ theory with that of Erasistratus is also insufficient. Vallance suggests that Asclepiades’ principle of ‘the motion (of matter) towards what is fine’ (
, PTLP) somehow arose as a reaction to Erasistratus’ PTKA.64 He does not, however, offer an explanation of how the one could have developed out of the other, and his analysis ultimately shows only that Asclepiades refuted PTKA, and that PTLP was not based on a principle of horror vacui, as he believes PTKA was. The fact that PTKA and PTLP are used by Erasistratus and Asclepiades to explain the same bodily processes, such as respiration, pulsation, appetite, the genesis of disease, etc., would seem to be adequately accounted for by the fact that both were doctors concerned to explain physiological and pathological phenomena. Given that Erasistratean PTKA relies on the impossibility of large-scale void, the fact that Asclepiades rejected it is entirely consistent with the conclusion that he postulated large-scale void. There is simply no reason to invoke Stratonic microvoid in the context of Asclepiades’ theory.
Conclusion
Galen, our only direct source on the subject, informs us that Asclepiades posited the existence of Epicurean-style void. As I hope to have shown, we have no reason to doubt Galen, and several different reasons to believe him. I conclude that Asclepiades’ pores contained large-scale void, and that it was in virtue of void that his onkoi were able to move at all. Given this conclusion, there can be little doubt that Asclepiades took his doctrine of void, and of void spaces within solid bodies, directly from Epicureanism. The fact that Asclepiades’ onkoi were identical to Epicurean atoms in most respects offers additional support. The purpose of this paper has been to examine Asclepiades’ pores in order to provide additional confirmation that his theory of matter was based directly on Epicurean atomism. One of the most interesting aspects of Asclepiades’ project, however, is not only his application of one of the leading Hellenistic physical theories to the field of medicine, but especially his deliberate modification and development of it. Asclepiades rejected some of the main tenets of Epicurean physics, namely the indivisibility of the atoms and the doctrine of theoretical minima, but also used the underlying theory to explain a much wider range of physiological, pathological and psychological phenomena in an original, comprehensive and coherent way. Although Asclepiades’ pores were basically Epicurean void gaps, their job within the Asclepiadean body seems to have been more complex and demanding than it had been in their previous, Epicurean home. But Asclepiades’ physiology, pathology and psychology cannot be fully understood without a proper appreciation of their fundamentally Epicurean roots.65
Acknowledgments
Parts of the paper were presented to a seminar in the Dept. of the History and Philosophy of Science, Cambridge, in February 2009, and I thank the audience for comment, in particular David Sedley and Roberto Polito. David Sedley was also kind enough to read the paper in more or less its final form, and his comments were very valuable. My thanks are also due to the anonymous reader for this journal for a kind review which improved the paper in a number of ways. The bulk of the research was carried out during a Research Fellowship funded by the Wellcome Trust (grant no. 082230), to which I wish to record my sincere gratitude.
Footnotes
1)E.g. Harig (1983), 44-45 and n. 17; Casadei (1997), 77-78, 89; cf. also Wellmann (1908), 695, though it does not seem to support his argument to the effect that Asclepiades’ theory can be traced via Erasistratus to Aegimius of Elis.
2)Notably Lonie (1965) and Gottschalk (1980), who both maintain that Asclepiades’ theory basically replicated that of Heraclides of Pontus; on Lonie’s discussion see also below, n. 60.
3)Vallance (1990), 44-91.
4)In a recent article, Leith (2009), I argued that the onkoi represent the most fundamental element of matter in Asclepiades’ system, and that their most basic characteristics exactly parallel those of Epicurean atoms, except for the fact that they are not atomic, but themselves physically divisible. There is evidence to suggest, however, that this divergence arose from Asclepiades’ deliberate modification of Epicurean doctrine, and I maintain that the distinctive features of his theory of matter can only be understood as being derived principally from Epicurean physics. The present contribution can be regarded as a counterpart to that study. In what follows, I shall avoid wherever possible making reference to controversial details regarding the nature of Asclepiades’ onkoi, in the hope that the conclusions of this paper will lend further plausibility to my arguments in the other, and vice versa.
5)For useful discussions of various kinds of distortive strategies employed by Galen in reporting the views of his medical opponents, see e.g. von Staden (1997), 192-96; Allen (2001); Tecusan (2004), 29-36.
6)Galen cites it at Hipp. Elem. 9.26 and 35 [1.487, 489 K. = p. 134.15-16, 136.24-25 De Lacy].
7)Gal. Lib. Prop. 8 [19.55 K. = p. 93.9-15 Boudon-Millot].
8)See Gal. Cur. Rat. Ven. Sect. 3 [11.257 K.], where he refers his readers to On the Opinions of Asclepiades books 5 and 6 and On Demonstration book 13 for a full refutation of Asclepiades’ theory of elements; cf. also Gal. MM 12.7 [10.852-3 K.], where On the Opinions of Asclepiades book 5 is cited for a more detailed treatment of one of his most favoured arguments against Asclepiades’ theory of matter, namely the failure of the onkoi to account for the phenomenon of pain.
9)Leith (2009).
10)Vallance (1990), 57: ‘If we look more closely at the context of those passages where Asclepiades is accused [by Galen] of selling out to Epicurus and negating continuum theory, some interesting results emerge. In each case the Methodists lurk not far away.’
11)Ibid. 57-58.
12)Caus. Morb. 1 [7.1-2 K.].
13)He refers explicitly to Caus. Morb. 7 [7.32-33 K.].
14)MM 10.267-68 K. He refers especially to the term 
. A similar argument is found at SMT 5.25 [11.781-84 K.], where Galen refers back to this passage of MM.
15)Vallance (1990), 56-57, 59.
16)Ibid., 91.
17)I assume that what is meant here is that matter is not a continuum, but divided up and separated by void as Calcidius goes on immediately to specify; cf. the sense of ‘divided’ in e.g. S.E. PH 2.5: 
.
18)On the Placita tradition in Calcidius and other sources, see Mansfeld (1990), 3112-17, and esp. 3113 n. 238 on this passage; on Asclepiades and the referent of Calcidius’ solidae moles, Switalski (1902), 53 and especially Polito (2007).
19)In Tim. 215: ‘aut enim moles quaedam sunt leves et globosae eaedemque admodum delicatae, ex quibus anima subsistit, quod totum spiritus est, ut Asclepiades putat.’ In this chapter Calcidius associates the term atomus only with Democritus and Epicurus.
20)Switalski (1902), 51-53. See also Polito (2006), 291-92, 297-99; and (2007), 316.
21)Note that the ps.-Galenic author may also have described the pores as 
, which would seem to offer additional support for understanding them as void spaces. In her new Budé edition of the treatise, Petit records that one of the two branches of the tradition has the additional words 
after 
, where vacuitates in the related Latin translation obviously points to an original reading 
. There is additional text, clearly corrupt, and Petit regards this as a later gloss accreted to the text in one branch (p. 131). I do not believe that it is such a gloss, but there is not space to go into the issues here.
22)The passage comes from a series of extracts added to Hero’s Definitions by a Byzantine compiler (cf. Heath (1921), 316). There is a similar account, likewise referring to Asclepiades’ doctrine of pores and onkoi, in Sextus Empiricus’ book Against the Geometers (M. 3.3-5, partially quoted below), and presumably both are drawing ultimately on a common source.
23)Vallance (1990), 47, arbitrarily dismisses the ps.-Hero passage as evidence: ‘[w]e might reasonably explain away this Heronic testimonium as showing signs of Galenic infection. More simply still we could dismiss both Hero and Dionysius: this might be best.’
24)As confirmed at S.E. M 3.5: 
(‘Second, that the parts of moisture and pneuma are gathered together from all sides out of onkoi perceptible by reason which are in motion forever’); Cael. Aur. Cel. Pass. 1.14.105: ‘… corpuscula intellectu sensa sine ulla qualitate solita atque ex initio concitata <et> aeternum moventia’ (‘… onkoi perceptible to reason, without any usual quality, having been in motion from the beginning and moving forever’). I accept Voss’ conjecture concitata for comitata of the editio princeps, as does Bendz. Gottschalk (1980), 57, claims that concitata results in a tautology with ‘aeternum moventia,’ but there is a distinction between moving forever and motion without beginning. Significantly, this was an important distinction also for Epicurus, who at Ep. Hdt. 43-44 (see following n.), expressing himself rather better than Caelius, asserts both the perpetual motion of the atoms and the fact that this has no beginning.
25)Epicur. Ep. Hdt. 43-44: 
… [44] 
(‘The atoms move continuously forever … For the nature of the void brings this about by separating each atom off by itself, since it is unable to lend them any support; and their own solidity causes them as a result of their knocking together to vibrate back, to whatever distance their interlinking allows them to recoil from the knock. There is no beginning to this, because atoms and void are eternal,’ trans. Long and Sedley). Cf. Lucr. 2.80-88.
26)Phys. 4.8, 215a 19-22.
27)For Epicurus’ use of the Aristotelian discussion of void, see Inwood (1981), esp. 283-84 on the argument that void entails perpetual motion.
28)The perpetual 
of the elements which is argued for at Pl. Tim. 58A-C is conceived as the eternal inter-transformation of the elements, and aims at establishing that the elements will never be separated out from each other entirely. Given that Asclepiades’ onkoi cannot be transformed into one another, his own conception of perpetual motion must have been significantly different.
29)Vallance (1990), 53, again dismisses this passage as evidence for Asclepiades’ doctrinal background without argument, remarking only that his use of the phrase ‘body does not pass through body’ ‘does not necessarily tell us much about Asclepiades’ true affiliations.’
30)The wonderful new edition of the papyrus by Manetti (2011), superseding that of Diels (1893), appeared just in time, and I have profited greatly from it in interpreting the papyrus remains. The phrase 
, ‘for the sake of argument’ is puzzling in the context, but there is no doubt that Manetti’s reading is correct. I assume that it conceals a reference to the previous formulation of the argument just seven lines before at col. xxxix 4, 
.
31)Democritus and Leucippus, along with ‘many other natural philosophers,’ are mentioned as upholders of the doctrine of void shortly before at Phys. 213b 1-2. Aristotle attributes the argument from growth explicitly to Leucippus at GC 325b 3-5.
32)The immediately subsequent lines (351-53) describe the distribution of nutriment in trees in particular, and again the permeation of the nutriment throughout the entire organism is emphasized, as in the argument attributed to Asclepiades and described by the Aristotelian commentators. A version referring to animals is found at 6.946-47, again with the same emphasis: ‘diditur in venas cibus omnis, auget alitque/ corporis extremas quoque partis unguiculosque’ (‘Food is distributed into all the veins, increasing and nourishing even the extreme parts of the body and the nails’). Note the salient point that the veins are not connected to the nails, and cannot therefore be responsible for growth by themselves.
33)See Alex. Mixt. 16.
34)So Todd (1976), 73-75. He points out there that the Stoics themselves would not have described their own theory of 
using the formulation ‘body passes through body.’
35)Asclepiades, however, is nowhere mentioned in Todd (1976).
36)Gal. Hipp. Elem. 9.35 [1.489-90 K = p. 136.23-26 De Lacy]: 
(‘but now for this present discourse it will be enough to say only this much, that none of the things that Asclepiades says in his book On Elements in answer to those who mix substances with each other through and through will touch those who say that the mixture is of their qualities only,’ trans. De Lacy; for the identification of the former group with the Stoics, see De Lacy’s commentary to p. 96.12 and 136.15-20). The anonymous scholiast on this passage has the following (ed. Moraux (1977), 50.241-45): 
(‘For this reason Galen also says that none of what was said by Asclepiades in his book On Elements in answer to those who mix substances with each other through and through will touch those who say that mixture is of their qualities only. He [sc. Asclepiades] said that body does not pass through body’).
37)Todd (1976), 74-81. He fails to acknowledge, however, that the disjunction ‘through body or through void’ which introduces Alexander’s refutation of the Stoic theory of mixture at Mixt. 5 ff., and which, Todd notes, ‘seems unnecessary when the Stoics would never have posited the latter theory’ (75), exactly matches the basic argument of the early atomists which Aristotle reports, as well as that of Asclepiades. He remarks at 79-80, referring to Phys. 213b 18-20, which he regards as the source of the Peripatetic development of the criticism ‘body does not pass through body,’ that Aristotle ‘in one case, because he is arguing against a specific aspect of the theory of void, … states the alternative of growth through body or through the void.’ But surely the reason for Aristotle having done so was rather that this was the form of the early atomist argument for void which he was reporting. We are not compelled to conclude with Todd that the form and use of the concept ‘body does not pass through body’ developed solely within the Peripatetic exegetical tradition.
38)Vallance (1990), 56; see also 115, where, referring to the pores, he speaks of ‘the disintegration of the walls of the passages – the solutio of the corpuscles which make up the pores.’
39)Lonie (1965), 128.
40)I shall examine the comparable Epicurean use of the term 
shortly.
41)E.g. Pigeaud (1981).
42)E.g. Casadei (1997).
43)On the possibility that the even more suggestive term 
was used by the ps.-Galenic author of Int., see above n. 21.
44)Gal. MM 2.4 [10.101 K.]: 
, where Asclepiades is named seven lines above; and similarly MM 13.2 [10.876 K.]: 
. The third occurrence, at Comp. Med. Gen. 6.16 [13.936 K.], appears within a chapter copied verbatim from the writings of Asclepiades, but this should be the first century AD pharmacologist Asclepiades Pharmacion, despite its suggestive references to onkoi and their dissolution: 
.
45)At M. 7.202, Sextus states that he dealt with Asclepiades’ doctrine in more detail 
.
46)Sextus uses both terms, once each: M. 3.5 (quoted above), and M. 8.220: 
. The ps.-Galenic author of Int. likewise uses both terms, once each, at 9 [14.698 K. = p. 21.14 Petit] (quoted above), and 13 [14.728-29 K. = p. 47.14-18 Petit]: 
, and notably 
, is also mentioned in several chapters of the Problemata of Cassius the Iatrosophist which otherwise show strong signs of Asclepiadean influence: see esp. chs. 77 [p. 65 Garzya and Masullo (2004)] and 82 [p. 66 Garzya and Masullo] (note that these chs. are printed as 76 and 81 in Ideler’s edition, at vol. I pp. 166 and 167 respectively). Asclepiades himself is said to have described the glands as 
, and therefore more receptive of matter at Probl. 41.13 [p. 55 Garzya and Masullo = ch. 40, p. 158 Ideler].
47)Viae throughout Cael. Aur. Cel. Pass. and Tard. Pass.; foramina at Cels. proem. 16.
48)Cf. also 
.
49)On the passage of eidola through a 
, see also Epic. fr. 24.46.13-16 Arr. According to Sedley’s convincing reconstruction, there is no reference to 
at fr. 31.4.1-4 Arr. = fr. 8 col. iv Sedley (1973).
50)Notably, Epicur. Nat. 25 P. Herc. 1191-12 sup. (Laursen (1997), 33 = fr. 34.26.11 Arr.) uses the term to describe openings through which matter passes into our bodies from outside. Cf. also Ep. Pyth. 111, Nat. 25 P. Herc. 1420, 2, 2 (Laursen (1995), 91 = fr. 35.10.9-15 Arr.).
51)If we assume that Caelius is translating Soranus’ original Greek here, then the form complexio suggests some such term as 
or 
, the former of which Galen uses in general statements that for Asclepiades everything is composed of onkoi: e.g. Gal. Ther. Pis. 11 [14.253 K.]: 
(sc. Asclepiades); cf. also Arist. DC 3.4, 303a 7-8, on atoms: 
. For the complex issue of Caelius’ relationship to his Soranian original in the Cel. Pass. and Tard. Pass., see especially van der Eijk (1999), 415-24.
52)At Cel. Pass. 3.13.110, Caelius explicitly cites Cicero as an authority for his rendering of 
by visum. He also refers to Tusc., without mentioning its title, at Tard. Pass. 1.6.180, though not on the subject of translation.
53)Cf. Cic. Fin. 1.19: ‘declinare dixit atomum perpaulum, quo nihil posset fieri minus; ita effici complexiones et copulationes et adhaesiones atomorum inter se, ex quo efficeretur mundus omnesque partes mundi quaeque in eo essent.’ (‘he said that the atom makes a very tiny swerve, – the smallest divergence possible; and so are produced entanglements and combinations and cohesions of atoms with atoms, which result in the creation of the world and all its parts, and of all that in them is,’ trans. Rackham, Loeb).
54)Lucr. 1.346-57, esp. 346-47, ‘praeterea quamvis solidae res esse putentur,/ hinc tamen esse licet raro cum corpore cernas’ (‘Besides, however solid things may be thought to be, here is proof that you may discern them to be of less than solid consistency,’ trans. Smith, Loeb).
55)See above, n. 47.
56)On this, see also the comments of Casadei (1997), 90.
57)Lucretius’ use of terms which primarily refer to two-dimensional shapes at 653-54 is further confirmation that he does not have a primary conception of the foramina as extended vessels or channels.
58)What precisely Epicurus’ conception of void was is of course another question, one which I have not sought to address here, but I have found myself persuaded by the arguments of Sedley (1982); for a different view, see Inwood (1981).
59)Leith (2009); see above n. 4.
60)Lonie (1965), 128-29, remarks that ‘so far as the 
in Asclepiades’ theory are 
, he seems to belong in the line of medical thought which begins with Strato.’ He does not address the Galenic, or non-Galenic, evidence on Asclepiades’ postulation of Epicurean-style void. Against his remark, it may be noted that in the Epicurean system the void interstices which must exist in solid objects are also imperceptible, and their existence has to be inferred. Lonie goes on to argue on other grounds that Erasistratus (and therefore Strato) are unlikely candidates as sources for Asclepiades’ theory (129-32), with a view ultimately to establishing Heraclides of Pontus as this probable source. But he does not return to the problem of Asclepiades’ pores and void, and appears to pass over the possibility of Epicurean influence simply by noting that the Epicureans ‘seem to have taken little interest in medical theory, although it is possible that Epicurus himself wrote 
’ (133). Lonie thus seems to take it for granted that any source of Asclepiades’ theory must have included a developed medical system, but this precludes the possibility of any innovation on Asclepiades’ part, and ignores any potential medical application of Epicurean atomism, as well as its actual medical application in the explanation of plague at Lucr. 6.1090-137, or in the analysis of the effects of various diseases on the mind at Lucr. 3.463-73 and 487-509.
61)Erasistratus’ principle of PTKA has often been associated with later theories of horror vacui in scholarship, but see Berryman (1997) for cautionary remarks.
62)See Gal. Nat. Fac. 2.6 [2.99 K. = Scr. Min. vol. III p. 173 Helmreich]; Ut. Resp. 2 [4.474 K. = p. 84 Furley and Wilkie]. Cf. Furley and Wilkie (1984), 34-35.
63)As pointed out by Furley (1989), 157, ‘[t]here is no direct evidence as to whether Strato made use of the principle of horror vacui in his physics … The theory of matter depends on the concept of the microvoid, whereas horror vacui is simply the view that there is no massed void; and the latter is equally true for Aristotle’s theory of matter, which denies the microvoid. Indeed the microvoid theory might be thought to be an impediment to horror vacui.’
64)Vallance (1990), 63-89; cf. also Vallance (1993), 699. As noted above, in the conclusion to his chapter on void, Vallance (1990), 91, suggests that Asclepiades posited ‘what may after all have been an Epicurean void.’
65)I dedicate this article to the memory of Bob Sharples, my teacher and then colleague at UCL. It is the last thing I gave him to read, and his comments were, as always, penetrating, encouraging and of enormous help. I owe him a very great deal.
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Funding
Funders who supported this work.
Wellcome Trust (2)
New Medical Papyri from Oxyrhynchus.
Dr Gonis, University College London
Grant ID: 082230
The Fragments of Asclepiades of Bithynia.
Dr Leith, University of Cambridge
Grant ID: 091617