The verb ἀντιπράσσειν means "to act against," "to oppose." In Marcus the term acquires a specific ethical meaning: any behaviour that breaks up the TERMcooperation of rational beings is counter-action; and since rational beings have been brought into being for cooperation, counter-action is a violation of TERMnature. From the verb is derived the adjective ἀντιπρακτικόν — "counter-active" — by which Marcus characterises anger and estrangement.

The usage is specifically Marcan: Med. 2.1 (twice); 9.23; 11.18. The conceptual background is the general Stoic opposition κατὰ φύσιν / παρὰ φύσιν, "according to nature / contrary to nature" (SVF III 4–9; DL VII 86–89).

The end of passage 02-01 turns on a play between two cognate words: "to act against (ἀντιπράσσειν) one another is contrary to nature; counter-active (ἀντιπρακτικόν) is to be vexed and to turn away." The ethical intuition is this: anger is not neutral, it is not merely an unpleasant experience — it is structurally isomorphic with the splitting of the body, the rupture of cooperation. Cf. Med. 11.18.4: "the nature of rational beings has been brought into being for joint action with one another … but the one who acts against the rest is a renegade."