Adiaphora literally means "things that admit of no differentiation," from ἀ-διά-φορον. In Stoic ethics it is the technical term for everything that is neither virtue nor vice, and which therefore does not determine whether a life counts as successful or failed. The Stoics draw a radically narrow classification of value:

This is a challenge to ordinary moral vocabulary. What people commonly call "goods" (health, success, kin) and "evils" (sickness, want, death) are, on the Stoic view, neither: they do not affect the quality of the soul, the sole site at which good and evil are localised.

SVF I 191, 192 (Zeno introduces adiaphora); III 117–168 (Chrysippus' extensive corpus); III 127–139 (the classification προηγμένα / ἀποπροηγμένα — Chrysippus, Antipater); DL VII 101–107; Stob. Ecl. II 79–85 W; Cic. De fin. III 50–58 (Cato in Cicero unfolds the doctrine); III 51–53 (the classification); IV 25–32, 39–48 (anti-Stoic critique); LS 58 ("Value and indifferents"). Anti-Stoic polemic: Plut. De Stoic. rep. 1047a–1050a — Plutarch attacks the fine distinctions as inconsistent.

In 02-11, the doctrine of adiaphora is the final conclusion of the longest passage in Book II:

θάνατος δέ γε καὶ ζωή, δόξα καὶ ἀδοξία, πόνος καὶ ἡδονή, πλοῦτος καὶ πενία, πάντα ταῦτα ἐπίσης συμβαίνει ἀνθρώπων τοῖς τε ἀγαθοῖς καὶ τοῖς κακοῖς, οὔτε καλὰ ὄντα οὔτε αἰσχρά. οὔτ' ἄρ' ἀγαθὰ οὔτε κακά ἐστι.

This is the canonical list of adiaphora in the Stoic tradition — four oppositions covering the whole spectrum of what is ordinarily taken to be fortune and misfortune: life/death, reputation/disgrace, pleasure/pain, wealth/poverty. Marcus derives the indifference of the list from Stoic theodicy: if it were genuine TERMevil, divine nature would not have allowed it to fall equally on the good and the bad; the distribution is equal and indiscriminate — therefore not evil; and therefore (by the converse law) not good either.

Connection with DOGMAdichotomy-of-control: in Epictetus, the doctrine of adiaphora is unfolded through the formula τὰ ἐφ' ἡμῖν / τὰ οὐκ ἐφ' ἡμῖν: adiaphora = what is not up to us = everything external to the ruling part. This is its operational form: the two lists coincide because, on the Stoic account, good and evil are localised exclusively in acts of assent, and assent is the only thing that is truly up to us. In Marcus the theme of adiaphora returns: Med. 4.20; 05-20 (the obstructor becomes ἀδιάφορον, like the sun or wind); 05-36; 06-32 (to the body all is indifferent, since it cannot differentiate; to the mind, indifferent is what is not its own activity); 07-31 (ἀδιαφορία toward what lies between virtue and vice — part of the soul's adornment); 7.66; 08-56 (another's προαιρετικόν is as ἀδιάφορον to me as his scrap of breath and flesh); 09-01 (a fresh list of ἀδιάφορα: life/death, fame/obscurity, pleasure/pain); 09-17 (the thrown stone: up and down are neither good nor evil; the external is ἀδιάφορον); 11.16.

Cicero's Latinisation: indifferentia / adiaphora; praeposita (= προηγμένα) / reiecta (= ἀποπροηγμένα). From adiaphora comes the modern "adiaphorism," a theological term for "things not essential to faith."