Another's choice — like another's breath. The passage works by decomposing "the neighbour" into parts along the Stoic canon of value. His προαιρετικόν — the faculty of choice, free will — is to my will just as TERMindifferent (ἀδιάφορον) as "his bit of breath and bit of flesh" (πνευμάτιον, σαρκίδιον, both in the belittling diminutive). The move is unexpected: normally προαίρεσις is the most valuable thing in a person, the only thing truly "ours." But another's προαίρεσις is not mine; it lies in his power, not mine, and so for my good it is as neutral as another's body. Cf. the DOGMAdivision of what is and is not up to us: another's choice falls under "not mine."

Each ruling part is a sovereign. τὰ ἡγεμονικὰ ἡμῶν ἕκαστον τὴν ἰδίαν κυρίαν ἔχει — "our ruling parts, each one, have their own authority (κυρία)." Even though we are made for one another (ἀλλήλων ἕνεκεν — the sociability axiom, cf. 08-59), in the moral sphere there is no seepage of one TERMruling part into another: my ruling part is a closed citadel (cf. 08-48), and my neighbour's vice does not enter it.

A neighbour's vice is not my evil — and this is God's arrangement. Hence the conclusion: DOGMAthe neighbour's κακία cannot be my κακόν. Marcus braces the ethics with theology: if another's vice were my evil, "my unhappiness would depend on another" — and this DOGMAGod did not will (οὐκ ἔδοξε τῷ θεῷ). Providence arranged the moral world so that the source of my ἀτυχεῖν ("being unfortunate") lies only in me. This is not indifference toward the neighbour (he is to be "taught or borne," 08-59) but a refusal to hand him the key to one's own good. The governing discipline is desire (what is good, evil, or indifferent); the sustaining one, action (the social frame ἀλλήλων ἕνεκεν).