Place in the book. A fine-grained analysis of pain and pleasure: how the ruling part keeps bodily affects within their bounds and does not turn a sensation into an "evil." The discipline of assent in pure form.
The ruling part — ἄτρεπτον. Let the TERMruling part (ἡγεμονικόν) of the TERMsoul be "unturned" (ἄτρεπτον) by the movements in the flesh — "smooth" (λεῖα, pleasure) or "rough" (τραχεῖα, pain); let it not "commingle" (μὴ συγκρινέσθω) with them, but "circumscribe itself" (περιγραφέτω) and TERMconfine those affects (πείσεις) to the parts. The DOGMAautonomy of the ruling part: the bodily is held within the bounds of the bodily.
The sympathy of one body. But since the body is "unified" (ἡνωμένῳ), the affect does reach the mind (διάνοια) "by that other sympathy" (συμπάθεια): the parts of one body are bound, as are the parts of one cosmos. Here one must not resist the sensation itself (αἴσθησις): it is "natural" (φυσική), neutral, unavoidable.
Add no ὑπόληψις. The decisive move: let the ruling part not add "of itself" (ἐξ ἑαυτοῦ) the TERMopinion (ὑπόληψις) "good or bad". Pain as a sensation is natural; only the verdict makes it a TERMpassion (πάθος). Between αἴσθησις and πάθος stands the DOGMArevocable assent: the sensation is not up to us, but the valuation is. Cf. Med. 8.49 ("add nothing of your own to what the impression reports") and 05-19 / 04-03 (things do not touch the soul).
Discipline and parallels. The principal discipline is assent (adding no valuation to the sensation); the secondary is desire (indifference to bodily pleasure/pain). Parallels: Med. 8.49; 04-03; 05-19.