Galen on the Stoic-Peripatetic Controversy about Mixtures: Qualities or Bodies?

1 Introduction

In Galen’s medical and philosophical thought, the notion of mixture is paramount, underpinning his physiology, therapeutics, and dietetics. In fact, on the one hand, material substances of the everyday regimen or with therapeutic purposes, such as foods, drinks and drugs, have a particular mixture of the hot, the cold, the dry and the wet. On the other hand, according to Galen, the nature of a living being is a mixture of the hot, the cold, the dry and the wet (De temp. H. 104, 1–3 K. I 675) and, therefore, one’s health and pathological states are conditioned by the balance or the imbalance of the elemental qualities (De temp. H. 16, 15–16 K. 534, 1–2). Therefore, medical treatment would consist in the interaction between the mixture of a living body and the mixture of a food, a drink or a drug, as these substances will replenish or reduce the quantity of hotness, coldness, dryness or moistness present in a living body so as to re-establish the right proportion.^[1]

However, it cannot be glossed over that mixture is primarily a physical process, in which primary elements mix and give rise to all compounded physical bodies, inanimate and animate. As such, the concrete, physical process of mixture is an essential basis for a thorough understanding of Galen’s physical system. Accordingly, I will pursue a twofold aim in this work. First, I will show Galen’s syncretic approach while expounding his theory of mixture (insofar as he attributes that theory equally to ‘Hippocrates’, Aristotle and the Stoics) and illustrate the reasons behind this approach (Section 2). Second, and more importantly, I will address Galen’s epistemological position concerning mixture’s constituents and answer the question of whether, according to Galen, are the qualities alone, conceived more Aristotelico as conceptually distinct from the body itself, to mix or if Galen viewed mixture, as the Stoics did, as a coextension of bodies (Section 3).

As is well-known, the Stoic and the Peripatetic schools expressed conflicting views of both how the primary elements mix and which place this theory should occupy within their philosophical system; in Galen’s time, this topic underwent a substantial renaissance, witnessed by Alexander of Aphrodisias’ De mixtione. As we will see, Galen assigns the epistemological status of πιθανόν to the Aristotelian and Peripatetic doctrines. This indicates that, to a certain extent, he joins this historical debate and is more closely aligned with Aristotle and the Peripatetics than with the Stoics. In this sense, this work can be situated in the context of recent studies by Kupreeva and van der Eijk, which contributed to identifying the Aristotelian and Peripatetic background of Galen’s elementary physics and of his psychophysiology of mixture.^[2]

2 Galen’s Syncretic Approach to Mixture

As I have previously said, when Galen describes his theory of mixture, which, borrowing the Stoic terminology, he calls ‘total’ (δι’ ὅλων), he attributes it equally to ‘Hippocrates’ (and the reference is more precisely – as it was well-known – to the Hippocratic text De natura hominis), Aristotle, and the Stoics. Let us consider the texts (T1–4).

T1. Galen, De elementis ex Hipp. K. I 489.6–11 (De Lacy 136.15–20):

καὶ μὲν δὴ καὶ ὅπως δι’ ὅλων κεράννυται τὰ κεραννύμενα, πότερα τῶν ποιοτήτων μόνων, ὡς Ἀριστοτέλης ὑπέλαβεν, ἢ καὶ τῶν σωματικῶν οὐσιῶν δι’ ἀλλήλων ἰουσῶν, οὐκ ἀναγκαῖον ἐπίστασθαι τοῖς ἰατροῖς· ὅθεν οὐδ’ Ἱπποκράτης ἀπεφήνατό τι περὶ τούτων, ἀλλ’ ἠρκέσθη μόνῳ τῷ δι’ ὅλων κεκρᾶσθαι τὰ στοιχεῖα.

Moreover, it is not necessary for physicians to understand how things are mixed through and through, whether the mixtures are of qualities only, as Aristotle supposed, or of corporeal substances that pass through each other; that is why Hippocrates said nothing about these matters but was content with the mere fact that the elements are mixed in their entirety. (Trans. De Lacy)

T2. Galen, In Hipp. nat. hom. comment. K. XV 32.1–11 (Mewaldt 18.27–19.7):

ὅτι γὰρ οὐχ ἕν ἐστιν, ἀλλὰ πλείω τὰ συντιθέντα τὴν | τοῦ ἀνθρώπου φύσιν, ἐπιδείκνυσιν ὁ Ἱπποκράτης, οὐ μὴν ὅτι γε μηδέν ἐστι τῶν τεττάρων στοιχείων εἰλικρινὲς ἐν τῷ σώματι. τὴν ἀρχὴν γὰρ οὐδὲ λέγουσιν οἱ τῆς δόξης ταύτης ἡγεμόνες τοῦτο. ἓν δή τι παρὰ τὰ τέτταρα, τὸ ἐξ αὐτῶν συγκείμενον, ἀποφαίνονται, ὥς γε τὴν τετραφάρμακον δύναμιν οὔτε κηρὸν οὔτε πίτταν οὔτε ῥητίνην οὔτε στέαρ, ἀλλά τι παρὰ ταῦτα ἓν ἄλλο, ὃ ἐξ ἁπάντων κραθέντων γέγονεν, οὔσης πάλιν καὶ αὐτῆς τῆς δόξης διττῆς· ἔνιοι μὲν γὰρ τὰς τέτταρας ποιότητας μόνας κεράννυσθαι δι’ ὅλων ἀλλήλαις λέγουσιν, ἔνιοι δὲ <καὶ> τὰς οὐσίας ἀπεφήναντο,^[3] Περιπατητικοὶ μὲν τῆς προτέρας δόξης προστάντες, Στωϊκοὶ δὲ τῆς δευτέρας.

For Hippocrates showed that what constitutes the nature of man is not one thing but many, not that none of the four exists in the body in its pure state. For the leading proponents of this doctrine do not say that this is the principle. Rather they hold that there is one thing over and above the four, and which is constituted from them, just as the power of the tetrapharmakon is neither wax, pitch, resin, nor fat, but something else over and above them, which is generated from the mixture of all of them, although this latter doctrine comes in two forms. For some people say that only the four qualities are mixed through-and-through with one another, while others hold that also the substances themselves are (the Peripatetics favour the former doctrine, the Stoics the latter). (Trans. Hankinson, slightly modified)

T3. Galen, De methodo medendi K. X 16.2–24:

τὸ γὰρ θερμὸν καὶ τὸ ψυχρὸν καὶ τὸ ξηρὸν καὶ τὸ ὑγρὸν Ἱπποκράτης μὲν πρῶτος εἰσηγήσατο, μετ’ αὐτὸν δ’ Ἀριστοτέλης ἀπέδειξεν· ἕτοιμα δ’ ἤδη παραλαβόντες οὐκ ἐφιλονείκησαν οἱ περὶ τὸν Χρύσιππον, ἀλλ’ ἐκ τούτων τὰ σύμπαντα κεκρᾶσθαι λέγουσι, καὶ ταῦτ’ εἰς ἄλληλα πάσχειν καὶ δρᾷν καὶ τεχνικὴν εἶναι τὴν φύσιν, ἅπαντά τε τὰ περὶ φύσεως Ἱπποκράτους δόγματα προσίενται, πλὴν περὶ μικροῦ τινός ἐστιν αὐτοῖς ἡ διαφορὰ πρὸς Ἀριστοτέλη […] διαφέρονται δὲ ἐν τῷ τὰς μὲν ποιότητας μόνας τὸν Ἀριστοτέλη δι’ ἀλλήλων ἰέναι καὶ κεράν-νυσθαι πάντῃ, τοὺς δ’ ἀπὸ τῆς στοᾶς οὐ ταύτας μόνας, ἀλλὰ καὶ τὰς οὐσίας αὐτὰς ὑπολαμβάνειν.

For Hippocrates was the first to propose the hot, the cold, the dry and the moist, and after him Aristotle proved them. And the followers of Chrysippus, when they accepted these things already to hand, were not embroiled in contention. Rather, they say that all the things are compounded from these [four elemental qualities], and that these things are affected by and act on each other, and that nature is craftsman. And they approve all the other doctrines of Hippocrates regarding nature, apart from one minor point which is a difference between them and Aristotle […]. However, they differ in this: Aristotle held that the qualities alone go through one another and mix together completely, whereas those from the Stoa suppose that not these qualities only but also the substances themselves do this. (Trans. Johnston-Horsley, slightly modified)

T4. Galen, De naturalibus facultatibus K. II 5.8–17 (Helmreich 104.6–15):

καὶ μέντοι καὶ τὸ κεράννυσθαι δι’ ἀλλήλων αὐτὰς ὅλας δι’ ὅλων Ἱπποκράτης ἁπάντων [ὧν ἴσμεν] πρῶτος ἔγνω· καὶ τὰς ἀρχάς γε τῶν ἀποδείξεων, ὧν ὕστερον Ἀριστοτέλης μετεχειρίσατο, παρ’ ἐκείνῳ πρώτῳ γεγραμμένας ἔστιν εὑρεῖν. εἰ δ’ ὥσπερ τὰς ποιότητας οὕτω καὶ τὰς οὐσίας δι’ ὅλων κεράννυσθαι χρὴ νομίζειν, ὡς ὕστερον ἀπεφήνατο Ζήνων ὁ Κιττιεύς, οὐχ ἡγοῦμαι δεῖν ἔτι περὶ τούτου κατὰ τόνδε τὸν λόγον ἐπεξιέναι.

Hippocrates was also the first to recognize that all these qualities undergo an intimate mingling with one another; and at least the beginnings of the proofs to which Aristotle later set his hand are to be found first in the writings of Hippocrates. As to whether we are to suppose that the substances as well as their qualities undergo this intimate mingling, as Zeno of Citium afterwards declared, I do not think it necessary to go further into this question in the present treatise. (Trans. Brock)

As we see, in these four passages where Galen’s syncretic approach is glaringly visible, the formulation is analogous and presents only slight variations: in Galen’s view, in fact, Hippocrates held that the primary elements mix completely (δι’ ὅλων κεράννυσθαι), and only afterwards did Aristotle and Zeno, Chrysippus, or the Stoics generally get hold of the theory – but there is a difference between them. For the former was convinced that only qualities completely mix, whereas the latter thought that corporeal substances or substances-cum-qualities also completely mix. Galen adds that, in most cases, it is not necessary for a physician to understand whether the qualities or the substances-cum-qualities mix. Hippocrates was content with the mere fact that the primary elements mix completely.

However, the theories that Galen mentions together are very different from one another both in terms of modalities and purposes. First of all, differently from what Galen held, the ‘Hippocrates’ of De natura hominis does not actually set up a theory of mixture of the four elements at all; he rather speaks, as regards the nature of man, of a mixture of the four humours, such as blood, yellow and black bile, and phlegm.^[4] Second, though they both rely on a system of four intertransmutable elements, the Aristotelian and Stoic theories are different: the former is based on a progressive division of constituents followed by a unification brought about by a qualitative interaction, and the latter presupposes a coextension of two or more bodies. Moreover, though both models account for the everyday processes of mixture, their main aims and justifications are different. If Aristotle’s account points to the generation of homoeomerous stuff, biological or inorganic materials, the Stoics from Chrysippus on used the total mixture to explain the complete interpenetration of pneuma or God and matter.

In the first place, such an approach can be explained if we take into account both Galen’s education^[5] and his own argumentative use of the authorities. In fact, it is typical of Galen’s overall thought to offer purposely syncretic interpretations and to build shifting alliances in order to pursue his arguments, though he is perfectly aware of the doctrinal discrepancies that exist between the authorities that he quotes, doing this even at the cost of distorting the sources from which he draws.^[6] For example, if, on this occasion, he teams up with these authorities, as well as with Aristotle, elsewhere he criticizes them both ferociously and without reservation for having posited the seat of the ruling part of the soul as in the heart rather than in the brain, as happens in De placitis Hippocratis et Platonis.

What, then, would be the point of putting all these diverse theories of mixture together? This is explained well by Vegetti, who has already highlighted the strategic role that this alliance between ‘Hippocrates’, Aristotle, and the Stoics plays for the creation of a ‘friendly tradition’ of continuum theories, as the Aristotelian and the Stoic theories were. We can say that Galen was a committed continuist, on a par with the Stoics and the Peripatetics. Therefore, he could take advantage of this alliance with the Stoics and Peripatetics to achieve one of his main polemical objectives: the rejection of older and more recent versions of atomism and corpuscularism, such as that of Asclepiades of Bithynia, who claimed the existence of void and centred his medical theories on the general assumption that the body was made up of invisible particles (ὄγκοι) and channels (πόροι).^[7]

Furthermore, it has to be stressed that by appealing to Hippocrates’ authority, Galen evades more contemporary and pressing questions, that is, those concerning the problem of the constituents of a mixture, which at that time profoundly stirred the major philosophical schools and led exponents of the Platonic and Peripatetic schools (and of corpuscularist medicine) to fight against Stoic corporealism. At first sight, to such questions Galen simply replies that, on the basis of Hippocrates’ doctrines, what he knows for sure is that the primary elements mix, though he does not want to make any pronouncement regarding how they mix, or whether the mixture involves qualities (as Aristotle upholds) or substances-cum-qualities (as the Stoics maintain).

3 Galen and the Stoic-Peripatetic Controversy about Mixtures: Qualities or Bodies?

However, an analysis of how Galen tackles this latter issue (on the constituents of a mixture) may be relevant from other points of view. In the first place, it suggests a philosophical reflection upon causality in the mechanism of mixture and the difference between the Peripatetic and Stoic accounts thereof. Second, and more importantly, we can see how Galen copes with doctrinal divergence, namely, in ways that are coherent with his general anti-dogmatic outlook and in accordance with the principles of his own epistemology.

It has been said that the aforementioned passages (T1–4), in which Galen explains the difference between the Peripatetic and Stoic concepts of a mixture’s constituents, must be considered pieces of unreliable doxography, as the basic categories of ποιότης (or, more precisely, ποιόν in the case of the Stoics) and οὐσία differed considerably between the Stoic and the Peripatetic traditions.^[8] Actually, though these passages might be doxographical,^[9] and we know that Galen uses doxographic resources, this does not mean that Galen’s report must be rejected or that its significance should be minimized. After all, the reference to substances-cum-qualities that Galen attributes to the Stoics and that Alexander also uses in De mixtione to describe the constituents of a mixture (De mixtione 216.26, Bruns) can refer to the Stoic acceptation of οὐσία as a material substrate, whereas ποιότης might indicate a second corporeal entity imbuing matter and capable of affecting it causally. For, according to the Stoics, qualities are also bodies and therefore have causal efficacy. Moreover, further confirmation of Galen’s reference to the Stoic corporealistic account in those cases is reflected by his shifting between the reference to substances-cum-qualities and the expression σωματικαὶ οὐσίαι, that is, corporeal substances, which are said to go through one another (τῶν σωματικῶν οὐσιῶν δι’ ἀλλήλων ἰουσῶν).

In these passages, an interesting problem arises regarding the notion of mixture, namely: how do the constituents interact during the process of mixture? Is such an interaction attributable to the Stoic concept of substances-cum-qualities or corporeal substances, wherein qualities are a second corporeal entity imbuing matter and capable of affecting it causally? Or, rather, are qualities alone understood – as mentioned – more Aristotelico, i.e. as conceptually distinct from the body itself? This distinction, in fact, entails a very different process of causation in each case. To Aristotle, qualities are the formal-efficient cause of the mechanism of mixture, since they first set in motion and carry out the process of mixture through a qualitative interaction.^[10] On the other hand, in Stoic theory, the question is slightly more complex if one does not want to superimpose the Aristotelian schema on the Stoic theory of causation. As Collette-Dučić and Delcomminette remark, it is always the active principle that plays the role of the causal agent, as in the case of pneuma or God mixing with passive matter, a case exemplified by the well-known Chrysippean paradox of the drop of wine which coextends through the entire sea.^[11] In this instance, the first, which transfers its activity onto the other, can be seen as the συνεκτικὸν αἴτιον or cohesive cause, whereas the second only favours and supports the process and, therefore, can only be seen as a cooperant cause (συνεργὸν αἴτιον).^[12] However, the basic difference between the two processes of causation remains that – in contrast to Aristotle’s view – according to the Stoics, only bodies can act and be acted upon, which is the hallmark that they (as the materialists of Plato’s Sophist) assign to true beings.

Although Galen gives us the impression of underestimating the discrepancy between the Stoics and Aristotle, he does mention an issue (regarding the type of causation) that goes beyond the subject matter of mixture, reflecting instead a broader key difference between the two schools, the Stoic and the Peripatetic, which makes these two theories incompatible. Hence, if Galen had answered this question, whether it is qualities that mix or corporeal substances-cum-qualities, he would have been compelled to side with one of the two philosophical schools. Choosing a side would have conflicted with his reiterated declarations of philosophical independence. How can he tackle this doctrinal dilemma (qualities or bodies) while preserving his syncretic approach?

In the epistemological gradation of certitude that we find in On my own opinions, Galen carefully distinguishes between that which he does not know and about which he cannot form judgement, that which he knows for certain (βέβαιον), and that which is simply convincing (πιθανόν), to which he often appeals in order to avoid the aphasia of radical Pyrrhonian Scepticism.^[13] And, in fact, Galen speaks of this Stoic-Peripatetic controversy in several passages; he knows the difference between the two theories of mixture and the arguments that were used against the Stoic corporealists at the time, and he seems to be determined to enter the Stoic-Peripatetic controversy, as he critically engages with the leading proponents of the two main contemporary models of mixture by assuming an active though anti-dogmatic part in the debate.

First, Galen shows that he is aware of the arguments used against the Stoics. In a passage from De experientia medica (T5), a treatise handed down not in Greek but in Arabic translation, Galen distinguishes two different and alternative theories of matter: the atomistic theory and one based on complete interpenetration, which seems to be the only possible alternative – albeit difficult to imagine:

T5. Galen, De experientia medica XIX, p. 122 (Walzer):

As for the view that composite bodies are permeated the one by the other, although nothing remains except this, yet it is something which one cannot easily imagine, and I am far from thinking of it to say, to say nothing of understanding it and knowing it. For that two bodies, or three and often four or five, should occupy the same place is a condition difficult to imagine and to think of. (Transl. from Arabic by Walzer)

Galen does not say whose theory he is attacking, but we can glean that it is positioned against the atomistic theory and is, therefore, continuist; in addition, Galen objects to the idea that two or more bodies cannot coexist in the same place in a similar vein as Alexander’s criticism of the Stoic total interpenetration of bodies. In both cases, coextension is ruled out by reference to the Aristotelian paradox of two (or more) bodies in the same place.^[14]

But Galen takes an even stronger position against the Stoic theory of total mixture in a passage from De placitis Hippocratis et Platonis (T6), where he tries to refute two theories of vision:

T6. Galen, De plac. Hipp. et Plat. VII 5 K. V 618.1–619.2 (De Lacy 452.29–454.7):

Μάλιστα δ’ ἂν πεισθείη τις τοῦτο γίγνεσθαι μαθὼν ὅπως εὔλογόν ἐστιν ὁρᾶν ἡμᾶς. ἀρχὴ δὲ καὶ τοῦδε τοῦ λόγου τοιάδε· τὸ βλεπόμενον σῶμα δυοῖν θάτερον· ἢ πέμπον τι πρὸς ἡμᾶς ἀφ’ ἑαυτοῦ σὺν ἐκείνῳ καὶ τὴν ἰδίαν ἐνδείκνυται διάγνωσιν, ἢ εἴπερ αὐτὸ μηδὲν πέμπει, περιμένει τινὰ παρ’ ἡμῶν ἀφικέσθαι δύναμιν αἰσθητικὴν ἐφ’ ἑαυτό. πότερον οὖν αὐτῶν ἐστιν ἀληθέστερον ὧδ’ ἂν μάλιστα κριθείη· διὰ τοῦ κατὰ τὴν κόρην τρήματος ὁρῶμεν, ὅπερ εἰ περιέμενε πρὸς ἑαυτὸ παραγενέσθαι τινὰ μοῖραν ἢ δύναμιν ἢ εἴδωλον ἢ ποιότητα τῶν ἐκτὸς ὑποκειμένων σωμάτων, οὐκ ἂν τοῦ βλεπομένου τὸ μέγεθος ἐγνώκειμεν, οἷον ὄρους εἰ τύχοι μεγίστου. τηλικοῦτον γὰρ εἴδωλον ἐνέπιπτεν <ἂν> ἀπ’ αὐτοῦ τοῖς ὀφθαλμοῖς ἡμῶν ἡλίκον ἐστὶν αὐτό, ὅπερ παντάπασιν ἄλογον, ἅμα τῷ καὶ κατὰ μίαν ῥοπὴν καιροῦ πρὸς ἕκαστον τῶν ὁρώντων, εἰ καὶ μυρίοι τύχοιεν ὄντες, ἀφικνεῖσθαι. τὸ δὲ ὀπτικὸν οὐχ οἷόν τε τοσαύτην ῥύσιν ἐκτεινόμενον λαμβάνειν ὡς περιχεῖσθαι παντὶ τῷ βλεπομένῳ σώματι· τοῦτο γὰρ ὅμοιόν ἐστι τῷ τῶν Στωϊκῶν σταλαγμῷ κεραννυμένῳ τῇ πάσῃ θαλάττῃ.

A person would be most convinced that this happens when he has learned the probable account of how we see. This account also begins in the following way. A body that is seen does one of two things: either it sends something from itself to us and thereby gives an indication of its peculiar character, or if it does not itself send something, it waits for some sensory power to come to it from us. Which of these alternatives is the more correct may best be judged in the following way. We see through the perforation at the pupil; if this perforation waited for some portion or power or image or quality of the external bodies underlying [our perception] to come to it, we would not discern the size of the object seen, which might be, for example, a very large mountain. An image of the size of the mountain would have come from the mountain and entered our eyes, which is utterly absurd. It is also absurd that at one moment of time the image should reach every viewer, even though they are countless. And the optic pneuma cannot extend itself and acquire such a stream so as to envelop the whole object being viewed; for this is comparable to the Stoic drop that mixes with the whole sea. (Trans. De Lacy)

As we see in this passage, Galen explicitly rejects the Stoic paradox of the drop of wine in the sea by classifying it as absurd. But which aspect of the theory of total mixture is Galen referring to? In the passage, two theories are discussed. The first, according to which the seen object sends something to us, seems to correspond to the Epicurean theory of the eidola. ^[15] In the second, according to which a sensory power comes from us to the seen object, an optic pneuma extends itself (ἐκτεινόμενον) and pours over (περιχεῖσθαι) the object viewed.

It seems, therefore, that the pneuma indeed reaches the seen object and does this in virtue of its extension (οἷόν τε τοσαύτην ῥύσιν ἐκτεινόμενον λαμβάνειν). But what might connect the Stoic total mixture to the pneuma that extends itself? I think that, as Galen views the optic pneuma as unable to extend itself and acquire such a stream to pour over the seen object (as the Stoic drop of wine cannot extend itself and mix with the entire sea), he criticizes the process of ἀντιπαρέκτασις by painting it as absurd (ἄλογον). This is undoubtedly quite striking, since the Chrysippean paradox, as mentioned, would visually represent the total interpenetration of pneuma and passive matter, i.e. the very crux of the Stoic philosophical system.

On the other hand, much more in line with what Kupreeva has shown as regards Galen’s elementary physics,^[16] we can discern traces of Galen’s inclination to think that, as Aristotle held, it is qualities themselves that are responsible for the mechanism of mixture. For, in contrast to the passages already analysed, Galen presents his opinion in a less rigid manner when he summarizes his own beliefs, that is, in De propriis placitis. In this text, Galen tackles the problem again, but adds something more (T7):

T7. Galen, De propr. plac. 188.21–189.17 (Boudon-Pietrobelli):

ὅτι μὲν ἐκ τῆς τῶν δʹ στοιχείων κράσεως ἅπαντα τὰ παρ’ ἡμῖν σώματα γίγνεται, βεβαίως γιγνώσκειν φημί· καὶ προσέτι δι’ ὅλων αὐτῶν κεραννυμένων, οὐχ, ὡς Ἐμπεδοκλῆς ἡγεῖτο, κατὰ σμικρὰ μόρια καταθραυομένων. εἴτε δὲ τῶν σωματικῶν οὐσιῶν ὅλων δι’ ἀλλήλων ἰουσῶν, εἴτε τῶν ποιοτήτων μόνων, οὔτ’ ἀναγκαῖον εἶναί φημι γινώσκειν, οὔτε ἀποφαίνομαι. πιθανώτερον δὲ εἶναι νομίζω, κατὰ τὰς ποιότητας γίγνεσθαι τὰς κράσεις.

I declare that I know for certain that all our bodies come from a mixing together of the four elements, and besides through their complete mixture, not as Empedocles believed, through being broken up into small particles. But whether [this happens] because the corporeal substances go entirely through one another or only the qualities, I neither consider it necessary to know, nor do I make any definite pronouncement [about it]. I think it more likely, however, that the mixtures occur according to the qualities. (Trans. Nutton, slightly modified)

In this passage, Galen initially says that it is not necessary to know whether mixture occurs when the corporeal substances go entirely through one another or only the qualities; however (δέ), he adds that he believes it is more likely (πιθανώτερον) that the qualities mix. But what degree of epistemological certitude does the adjective πιθανός express? Chiaradonna has underlined that Galen employs the concept of πιθανόν to indicate what cannot be attained through the two criteria of certain knowledge, i.e. experience and reason.^[17] Even though – and this is indisputably true – Galen’s πιθανόν does not coincide with the maximum of epistemological certitude, Debru has shown that throughout Galen’s corpus the adjective πιθανός can have different meanings. At times, Galen utilizes the adjective to simply mean ‘persuasive’ or ‘convincing’, but ultimately false. In this regard, Galen occasionally uses the term in reference to his adversaries’ opinions or theories, which he commits himself to refuting and dismissing.^[18] At other times, πιθανός can refer to a plausible but still provisional explanation that may turn out to be true, a theory in the transitory stage in the search for truth (ἐγγὺς ἀληθείας) that still lacks scientific proof (ἐπιστημονικὴ πίστις). In these cases, the adjective πιθανός has degrees of plausibility, expressed by Galen’s use of comparatives and superlatives.^[19]

Debru’s account seems further confirmed by a passage from De elements (T8). For in the same context and with regard to the same question, even though Galen does not use the adjective πιθανός, he reformulates this concept. He takes a proper position towards the issue of causality, even though it is indirect and allusive.

T8. Galen, De elementis sec. Hipp. 9 K. I 489.13–490.15 (De Lacy 136.22–138.14):

εἰρήσεται δὲ κἀν τοῖς τῆς θεραπευτικῆς μεθόδου περὶ τῆς χρείας αὐτῶν ἐπὶ πλέον, ἐν δὲ τῷ παρόντι τοσοῦτον εἰπεῖν ἀποχρήσει πρὸς τὸν ἐνεστῶτα λόγον, ὅτι τῶν ὑπ’ Ἀσκληπιάδου λεγομένων ἐν τῷ Περὶ στοιχείων βιβλίῳ πρὸς τοὺς ὅλας | δι’ ὅλων κεραννύντας ἀλλήλαις τὰς οὐσίας οὐδὲν ἅψεται τῶν κατὰ τὰς ποιότητας μόνας κεράννυσθαι λεγόντων, ὥστ’ εἰ καὶ μὴ δι’ ἄλλο τι, διὰ γοῦν τὸ ἀσφαλὲς αἱρετέον τὸ δόγμα καὶ λεκτέον, ὡς ἐν τῷ μίγνυσθαι τῷ ὕδατι τὸν οἶνον, εἰ τύχοι, καὶ καταθραύεσθαι μέχρι σμικροτάτων ἑκατέρου τὰ μόρια δρᾶν καὶ πάσχειν αὐτοῖς εἰς ἄλληλα συμβαίνει καὶ μεταδιδόναι τῶν ποιοτήτων ἀλλήλοις ἑτοιμότερον, ὅσῳ περ ἂν εἰς ἐλάττω καταθραυσθῇ, καὶ διὰ τοῦτο κινοῦσιν ἐπὶ πλεῖστον οἱ μιγνύντες ἀλλήλοις τὰ τοιαῦτα τὴν εἰς ἐλάχιστον διαίρεσιν αὐτῶν μηχανώμενοι. καὶ μὲν δὴ καὶ τὸ μᾶλλον ἑνοῦσθαι τὰς ποιότητας ἀλλήλαις τῶν ἐπὶ πλέον ἀναμιχθέντων τε καὶ χρονισάντων ὁμολογεῖ τῷ λόγῳ. χρόνου γὰρ δεῖται τὰ σμικρὰ μόρια τῶν κεραννυμένων, ἵν’ εἰς ἄλληλα δράσῃ καὶ πάθῃ τελέως καὶ οὕτως ἓν ἀπεργάσηται τὸ ὅλον καὶ ὅμοιον ἑαυτῷ πάντη.

And I shall speak at length of the use of mixtures in the books of Therapeutic method; but now for this present one, and also it will be enough to say 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 they [the substances] are mixed in the qualities only; therefore, if for no other reason, at least for safety’s sake (διὰ γοῦν τὸ ἀσφαλές) we should pronounce as our choice the view that in the mixing of wine with water, for example, and in the breaking up of the parts of each into smallest bits, it happens that each of them acts on the other and is acted on by it, and that they share their qualities with each other the more readily the smaller the bits into which they have been broken; and for that reason those who are mixing such things together agitate them as much as possible, thus contriving that the division be to the smallest parts. Moreover, it is concordant with the reasoning that the qualities of things that have been mixed more thoroughly and for a long time are more closely united. The small parts of the things being mixed need time to complete their interaction and thus make the whole one and the same throughout. (Trans. De Lacy, slightly modified)

As we see, Galen does not identify Asclepiades’ polemical target, nor does Galen use his standard formulation ‘corporeal substances’ or ‘substances-cum-qualities’; in this passage, he only draws a contrast between those who mix substances and those who mix qualities (τῶν κατὰ τὰς ποιότητας μόνας κεράννυσθαι λεγόντων), which seems to be congruent with the other passages that we have analysed previously, where Galen draws a distinction between Aristotle and the Stoics: as highlighted before, in Aristotle’s view it is the qualities that are responsible for the mechanism of mixture, whereas according to the Stoics it is the bodies (‘corporeal substances’ or ‘substances-cum-qualities’).

Regarding this very passage, Hankinson observes that Galen seems to be attempting to sidestep the issue of causality.^[20] I would stick more closely to the textual evidence and would reformulate it slightly differently, in pursuit of two results. In the first place, we could single out with more precision Galen’s own peculiar position towards causality’s involvement in the mechanism of mixture. Secondly, by means of a comparison of the terms used by Galen, we could glean that, at least in some cases, the notion of πιθανόν, although it does not attain scientific certitude, can be instrumental in coping with doctrinal incongruities.

For if, up to now, Galen had only had recourse to the concept of πιθανόν as regards this philosophical conundrum, here Galen is saying 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 they (the substances) are mixed in the qualities only” (ὅτι τῶν ὑπ’ Ἀσκληπιάδου λεγομένων ἐν τῷ Περὶ στοιχείων βιβλίῳ πρὸς τοὺς ὅλας | δι’ ὅλων κεραννύντας ἀλλήλαις τὰς οὐσίας οὐδὲν ἅψεται τῶν κατὰ τὰς ποιότητας μόνας κεράννυσθαι λεγόντων). Even further, he overtly declares that (at least for safety’s sake) this opinion should be favoured because “it lies on firmer ground” (ἀσφαλές): διὰ γοῦν τὸ ἀσφαλὲς αἱρετέον τὸ δόγμα καὶ λεκτέον. By reading this textual locus more carefully and comparing it with the others, we can make two inferences:

• (1) The usage of the verbal adjectives in -teos, which expresses the idea of duty, strongly emphasises Galen’s choice (αἱρετέον/λεκτέον). In a rather ingenious formulation, Galen stands for a dogma that does not explicitly belong to any dogma. Galen is taking an indirect position consistent with the Peripatetic doctrine, even though it does not coincide with a dogmatical position.

• (2) This consistency, however, has limits because after comparing the other anthologized passages, we can say that this is restricted to the realm of what is πιθανόν. Nevertheless, we can agree that there are cases where what is πιθανόν – or better, πιθανώτερον – is not necessarily to be underestimated or despised because (although it does not coincide with the scientific demonstration) Galen can appeal to it on at least some occasions, as it gives him room for manoeuvre between scepticism (and its aphasia) and dogmatism and may prove to be very useful for articulating his own opinions – especially regarding popular and much-disputed topics.

We may also note that (1) and (2) do not jeopardise Galen’s syncretic approach to the mixture. Galen’s having recourse to what is πιθανόν is an anti-dogmatical way of entering the fervent dispute about qualities or bodies. The fact that he proposes a ‘convincing’ or ‘persuasive’ answer to the question, as long as it is deprived of scientific basis, does not risk his geometric triangulation between ‘Hippocrates’, Aristotle, and the Stoics, based on a firm principle, a quadripartite elemental system that underpins a continuum theory of matter.

4 Conclusions

As we have seen, this article has focused on two aspects relating to Galen’s conception of mixture, understood as an elementary physical process. In Section 2, I pointed to the twofold reason for Galen’s syncretic presentation of his own account of mixture. In fact, as we saw, he declares that ‘Hippocrates’, Aristotle, and the Stoics were in substantial agreement in holding that the hot, the cold, the dry, and the wet mix in their entirety (which, as in the Stoic terminology, he calls a δι’ ὅλων mixture). However, as I pointed out, these three theories differ significantly from one another if considered singularly. On the one hand, I explained Galen’s syncretic approach to mixture by underlining that it is typical of Galen’s general approach to group several authorities together when he needs to back up an argument. On the other hand, apart from the rhetorical use of these authorities, there is a deeper reason why Galen builds an ad hoc strategic alliance between the Stoics and the Peripatetics: both philosophical schools were continuist, like Galen, and one of the objectives of his medical-cum-philosophical system was the rebuttal of both older and more recent versions of atomism/corpuscularism.

In Section 3, I addressed an aspect connected to the theory of mixture that proved to have relevant implications regarding Galen’s own way of developing his theory of mixture. For, as Galen was well aware, the Stoic and the Peripatetic schools provide two very different explanations when it comes to the causal factor involved in the mechanism of mixture: according to the Aristotelians, the qualities alone set in motion and carry out the process of mixture, whereas the Stoics, in conformity with their own corporealist physics, attribute this role to the substances-cum-qualities (this controversy, which powerfully comes to the fore in Alexander’s De mixtione, is actually part of a far-reaching debate that sets different schools from the post-Hellenistic period onwards – the Platonic, the Peripatetic, and even the Epicurean – against the Stoics and their corporealism). In this section, I highlighted that despite his own reiterated declarations of philosophical independence, Galen actively – although anti-dogmatically – enters this historical debate in accordance with his own epistemological principles. On the one hand, he affirms (in his De propriis placitis) it to be πιθανώτερον that the qualities mix, and insists (in his De elementis), that it is ἀσφαλές, saying that the arguments that are used against those who mix substances (i.e. the Stoics) cannot be used against those who mix qualities alone.

This does not mean that Galen is certain that qualities are responsible for activating the mixture process. To be βέβαιον, this claim would have needed to be corroborated by scientific demonstration or empirical evidence, which has not been noticeably given. Instead, he reacts by expressing himself in terms consistent with the view and arguments of the Aristotelians of his time. However, he also confines this consistency to the more flexible realms of what is πιθανόν. By resorting to what is πιθανόν, in this case, he obtains two results: (1) does not expose himself to accusations of dogmatism but, at the same time and in his method, enters the ongoing controversy about qualities and bodies without taking a definitive position, and (2) he preserves his syncretic theoretical structure which, as we saw, finds its linchpin in the defence of a medical-cum-philosophical continuism.