Human beings are members (μέλη) of a single body: hands, feet, eyelids, the rows of upper and lower teeth. Cooperation among them is not chosen — it is inscribed in the very constitution of the organism. The eyelid does not "decide" to cover the eye; the lower teeth do not "come to an agreement" with the upper; they work together because otherwise the body would not be a body. So too rational beings cooperate not from good will but from their own nature — otherwise they fall away from the whole, like a hand cut off.

Med. 2.1: "we have been brought into being for cooperation, like feet, like hands, like eyelids, like the rows of upper and lower teeth" (γεγόναμεν γὰρ πρὸς συνέργιαν ὡς πόδες, ὡς χεῖρες…). Unfolded at Med. 07-13: "as members in a single body, so are rational beings, in their separate bodies, arranged for one common cooperation." Here Marcus also notes the Greek play on words: μέλος (member, limb) and μέρος (part) — to become a member, not merely a part, is to love one's neighbour from nature, not from constraint. Cf. 07-19 (bodies cooperating with the Whole "as the parts of our body with one another"). See also 08-34 (the severed hand as the image of the person who has cut himself off from society; yet a human is granted to grow back); 09-05 (to be a "member" (μέλος) is also to act: inaction severs one from the body no less than an anti-social deed); 09-42 (the eye demands no wage for seeing, nor the feet for walking: an organ working by its own constitution "has what is its own").

In passage 02-01 the image works as the concluding argument: once it has been said that one's neighbour is TERMkindred by reason, the bodily image of cooperation (TERMsynergia) is brought in, and TERMcounter-action then turns out to be not a moral fault but a physiological disorder — as if the eyelid were to struggle with the pupil. See the kindred image cooperation and the supporting doctrine DOGMAunity-of-cosmos.