Why doesn't oil combine together with other liquids?
Because, since it is viscous and dense and unified and not cut up into fine parts like other liquids, it does not have space for another liquid to move into it and combine with it.
Some things that are joined, however, are joined with one another by mixture, like the qualities of the elements. They have primary qualities that are completely concealed and that produce other [qualities], but are able to be separated and liberated by nature once again. Honey-wine and sour-wine imitate nature, since to our perception they seem to exist as a mixture. In truth, however, and with respect to their substantial nature, they are not like the elements.
Other things are joined by juxtaposition, like water and oil; still others are joined by combination, like barley with wheat; others by cementing, like stone with stone; others by adhesion and similar processes, like blood with flesh or marrow or bone; others by nailing, like wood to wood because some nails were fitted between them; others, by attachment and weaving together, like links in a chain.
But as for ensouled things, like wrestlers*, the soul isn’t joined with with the body in any these ways. That would be too absurd. Instead, the soul joins the body through a kind of suitable medium, which is to some extent receptive of the nature of both. And it [sc. the medium] embraces both a created and contrived thing and combines the incorporeal with the corporeal, the immortal with the corruptible, the pure with the impure, the divine with the earthly, as the discussion will show.
For when the blood is concocted in the liver and changed by the localized balanced proportion of heat and moisture, it generates a vapory pneuma. When this rises with the blood through the hollow-vein towards the heart, as it is heated and refined more, it [sc. the pneuma] becomes air-like. And again, when it is sent up through the carotid artery towards the base of the brain, being guided there by nature’s providence, casting off the immoderate boiling in accordance with a certain peculiar natural quality accompanying the coldness of the brain, the pneuma becomes aitherial, which is the soul’s instrument for activity.
So, just as wild horses are chastened by a bridle, so this [pneuma] is bridled by a certain unspoken natural capacity. Furthermore, it is indeed through respiration that the air that has come into the heart is refined and goes up through the arteries towards the head, and it is made nourishment of the aetherial and psychic pneuma. If [the air] meets a body, let it strengthen the body; but if it meets finest, purest, most radiant [pneuma], then [let it strengthen] the rational soul, being somehow a corporeal incorporeal, an intermediate bound between extremes of contrary substance.
When this pneuma is properly stable, in everything it does, it manages, with the soul, to act rationally [κατὰ λόγον]. But when it is cooled immoderately and compressed and thickened, it becomes unsuitable for the intense activity of the soul [and] makes the activities idle and sluggish. When it has been cooled and thickened extremely immoderately, the generated body also causes the soul to depart due to the unsuitability of the substance, as in the case of lethargy, torpor and a draught of cold poison. On the other hand, when it is heated immoderately and is moved more than is needed, it causes the soul to act immoderately in accordance with the soul’s displacement [κατὰ τὰς ἐκστάσεις τῆς ψυχῆς] in [cases of] phrenitis. When this affection becomes even stronger, after it is exhausted, it will make the soul depart again by not preserving their being bound together.
Consider with me a different work of god. For since it was fated that it [sc. the soul] be confined from the heavenly and divine body to an earthly body, [the god] contrived the descent in shape, structure and colour. For the head itself it formed into a sphere, just like a little heaven. It arranged the brain—bright and without excess, having given seven passages to it representing the number of the movers of the stars—to rise above the whole body. For heaven, too, rises above everything in the world of coming to be and passing away.
*the image is of two people embracing and holding on to one another.
Διὰ τί τὸ ἔλαιον οὐδενὶ τῶν ὑγρῶν ἀναμίγνυται;
ὅτι γλίσχρον ὂν καὶ παχυμερὲς καὶ ἡνωμένον καὶ μὴ τεμνόμενον εἰς λεπτὰ μόρια καθάπερ τὰ ἄλλα ὑγρά, οὐ δίδωσιν χώραν ἑτέρῳ ὑγρῷ ἐγκαταβληθῆναι εἰς αὐτὸ καὶ ἀναμιχθῆναι αὐτῷ·
τὰ δὲ ὁμιλοῦντα ἑαυτοῖς ὁμιλεῖ τῶν κατὰ τὴν κρᾶσιν, ὡς αἱ ποιότητες τῶν στοιχείων παντελῶς ἔχουσαι τὰς πρώτας ποιότητας ἀφανιζομένας καὶ ἑτέρας γεννωμένας, δυναμένας δὲ πάλιν ὑπὸ φύσεως χωρισθῆναι καὶ σωθῆναι. τὸ δὲ μελίκρατον καὶ τὸ ὀξύκρατον μιμεῖται τὴν φύσιν, τῇ αἰσθήσει μὲν νομιζόμενα κατὰ κρᾶσιν, εἶναι μὴ ὄντα δὲ κατὰ ἀλήθειαν· καὶ πρὸς τὴν φύσιν οὐσιωδῶς, ὥσπερ τὰ στοιχεῖα.
τὰ δὲ κατὰ παράθεσιν, ὡς ὑδρέλαιον· τὰ δὲ κατὰ μῖξιν, ὡς κριθὴ πυροῖς· τὰ δὲ κατὰ κόλλησιν, ὡς λίθος λίθῳ· τὰ δὲ κατὰ πρόσφυσιν καὶ ὁμοίως, ὡς αἷμα σαρκὶ ἢ μυελῷ ἢ ὀστῷ. τὰ δὲ κατὰ γόμφωσιν, ὡς ξύλον ξύλῳ διὰ γόμφων τινῶν ἐν μέσῳ βαλλομένων. τὰ δὲ κατὰ ἀντοχὴν ἑαυτῶν καὶ περιπλοκήν, ὡς κρίκος κρίκῳ.
ἐπὶ δὲ ἐμψύχων, ὡς ἐπὶ παλαιόντων, κατ' οὐδένα τούτων τῶν τρόπων μίγνυται ἡ ψυχὴ σώματι. διὰ τὸ πολλὴν ἐπάγεσθαι ἀτοπίαν [mss. ἀντοπίαν], ἀλλὰ μᾶλλον κατ' ἐπιτηδειότητα ὁμιλεῖ σώματι ψυχὴ διὰ μέσου τινός, ὅπερ ἀμφοτέρων ἀναδεχόμενον φύσιν ποσῶς· καὶ προσφιλεῖ γινόμενον καὶ σοφιζόμενον, ἀμφότερον μίγνυσι τὸ ἀσώματον τῷ σώματι, τὸ ἀθάνατον τῷ φθαρτῷ, τὸ καθαρὸν τῷ ἀκαθάρτῳ, τὸ θεῖον τῷ γηΐνῳ, ὡς ὁ λόγος δείξει·
ἐν γὰρ τῷ ἥπατι τοῦ αἵματος πεττομένου καὶ μεταβαλλομένου ὑπὸ τῆς αὐτόθι συμμέτρου θερμότητος καὶ ὑγρότητος, γεννᾶται πνεῦμαἀτμοειδές· τοῦτο δὲ διὰ τῆς κοίλης φλεβὸς ἀνιὸν μετὰ τοῦ αἵματος πρὸς καρδίαν, καὶ ἐπὶ πλέον θερμαινόμενον καὶ λεπτυνόμενον, γίνεται ἀεροειδές· καὶ πάλιν ἀναπεμπόμενον διὰ τῶν καρωτίδων ἀρτηριῶν πρὸς τὴν βάσιν τοῦ ἐγκεφάλου κατὰ πρόνοιαν φύσεως ἐκεῖσε παιδαγωγούμενον κατ' ἰδιότητά τινα φυσικὴν ὑπὸ τῆς τοῦ ἐγκεφάλου ψυχρότητος ἀποβαλὸν τὴν ἄμετρον ζέσιν, γίνεται πνεῦμα αἰθεροειδές, ὅπερ ὄργανόν ἐστι ψυχῆς πρὸς ἐνέργειαν·
ὥσπερ ἄγριος ἵππος ὑπὸ χαλινοῦ σωφρονιζόμενος, οὕτω δὲ τοῦτο χαλιναγωγούμενον ὑπό τινος ἀρρήτου φυσικῆς δυνάμεως· ἔτι γε μὴν διὰ τῆς ἀναπνοῆς ὁ εἰσιὼν ἀὴρ ἐν τῇ καρδίᾳ λεπτυνόμενος καὶ ἀνιὼν διὰ τῶν ἀρτηριῶν πρὸς ἐγκέφαλον, καὶ αὐτὸ τροφὴ καθίσταται τοῦ αἰθεροειδοῦς καὶ ψυχικοῦ πνεύματος· ὅπερ εἰ μὲν σῶμα τυγχάνει, προσωκείτω τῷ σώματι, εἰ δὲ λεπτότατον καὶ καθαρότατον καὶ διαυγέστατον φιλιοῦται, ψυχῇ λογικῇ σῶμα ἀσώματόν πως ὑπάρχον καὶ δεσμὸς ἔμμεσος τυγχάνει τῶν ἄκρων ἐναντίαν οὐσίαν ἐχόντων·
τοῦτο τὸ πνεῦμα καλῶς μὲν εὐσταθοῦν διάγει ψυχῇ πάντα κατὰ λόγον ἐνεργεῖν· ἀμέτρως δὲ ψυχόμενον καὶ πιλούμενον καὶ παχυνόμενον καὶ ἀνεπιτήδειον γινόμενον πρὸς ἐνέργειαν σύντονον ψυχῆς ποιεῖ τὰς πράξεις ἀργοτέρας καὶ νωθροτέρας· ἀμετρότατα δὲ ψυχθὲν καὶ παχυνθὲν καὶ σῶμα γενόμενον παρασκευάζει ταύτην ἀφίστασθαι διὰ τὸ ἀνεπιτήδειον τῆς οὐσίας, ὡς ἐπὶ ληθάργων καὶ κάρων καὶ πόσεως ψυχρῶν δηλητηρίων· πάλιν δὲ θερμανθὲν ἀμέτρως καὶ πλέον τοῦ δέοντος κινούμενον, παρασκευάζει ψυχὴν ἀμετρότερον ἐνεργεῖν κατὰ τὰς ἐκστάσεις τῆς ψυχῆς ταῖς φρενίτισιν· ἔτι δὲ πλέον τοῦτο παθὸν καὶ ἐκδαπανηθὲν ποιήσει πάλιν ψυχὴν ἀφίστασθαι τῷ μὴ εὐπορεῖν τοῦ δεσμοῦντος ἀμφότερα.
θεώρει δέ μοι ἕτερον ἔργον θεοῦ· ἐπειδὴ γὰρ ταύτην ἔμελλεν ἀπὸ σώματος οὐρανίου καὶ θείου κατακλείειν σώματι γηΐνῳ, σοφίζεται τὴν κάθοδον σχήματι, κατασκευῇ, χρώματι. αὐτὴν μὲν γὰρ τὴν κεφαλὴν σφαιροειδῆ διετύπωσε, καθάπερ μικρὸν οὐρανόν· τὸν δὲ ἐγκέφαλον λαμπρὸν καὶ ἀπέριττον ἔταξε δεδωκὼς αὐτῷ πόρους ἑπτὰ τῶν κινουμένων ἀστέρων τὸν ἀριθμὸν διατυπώσας. ὑπερέχειν δὲ τοῦ παντὸς σώματος· καὶ γὰρ ὁ οὐρανὸς ὑπερέχει πάντα τὰ ἐν γενέσει καὶ φθορᾷ.
Pseudo-Alexander, Problems, 2.67