The adjective "kindred / akin," designating shared participation in a common nature. In the Stoics, συγγενής acquires a specific sense: human beings are kindred to one another not by blood, but by TERMintellect (νοῦς), being particles of a single cosmic Logos. The notion is the ethical correlate of the doctrine of DOGMAoikeiōsis and of Stoic cosmopolitanism: granting citizenship rights to every rational being.

SVF III 333–339 (the doctrine of the cosmopolis); Cic. De fin. III 62–68; Sen. Ep. 95.52; Epict. Disc. 1.13.3–4; 1.9.1–6. In Marcus: Med. 2.1; 3.4; 07-13 (a member of the system of rational beings — kinship as co-membership); 07-22 (συγγενεῖς — those who stumble are your kin, hence to be loved); 09-09 (πρὸς τὸ ὁμογενές/συγγενές σπεύδει — all strives toward the akin; a human cannot be severed from a human); 09-22 (the neighbour's ἡγεμονικόν is συγγενές — kinship as the ground of gentleness, not anger); 11-09 (ἀλλοτριωθεὶς πρὸς τὸν φύσει συγγενῆ καὶ φίλον — the man embittered at an obstructor is called a deserter on a par with the man who fled in fear: kinship survives the conflict); 10.6. In Book XII — 12-26 (the συγγένεια of a man with the whole human race, with the qualification: not αἱματίου ἢ σπερματίου but νοῦ κοινωνία). In Books I–IV: 02-13 (συγγένεια), 03-04 (συγγενὲς πᾶν τὸ λογικόν — everything rational is akin), 03-11 (συγγενής of one's neighbour).

In 02-01 συγγενής operates as a key transition: from diagnosis ("my neighbour errs out of ignorance") to conclusion ("I cannot be angry with one who is kindred to me"). Marcus stresses that the kinship is not "by blood or by seed," but by TERMintellect and the TERMdivine portion — a formulation that goes back to Epictetus (Disc. 1.9: "you have one father — Zeus"). See unity-of-cosmos.