As I mentioned in a previous post, I think that it is unlikely that when Paul states that Philemon and Onesimus are adelphoi en sarki (“brothers in the flesh”), that he means that they are both human beings. I say this for at least five reasons, the first of which I’ll elaborate here.
First, this is not at all an assumption that would have been common in the ancient world. On the contrary, the realities of slavery revealed them to be considered as less than human. They were thought of as property and slavery was “a state of absolute subjection. The slave has no kin, he cannot assume the rights and obligations of marriage; his very identity is imposed by the owner who gives him his name” (Wiedemann, pp. 202-203). Slaves were treated according to Aristotle’s sentiment that a slave is a “living tool, and the tool is lifeless.”
While Roman legal texts distinguished slaves from other commodities that could be owned, our understanding of the realities of slavery must go beyond the legal texts and take into account the “roles played by power abuse and violence” (Wessels, p. 147). Wessels maintains that this more comprehensive view reveals that “slaves were in reality nothing but chattel, movable possessions, which could be bought and sold by owners without any consideration of the human and cultural relations that slaves might have had” (Wessels, p. 148).
Jennifer Glancy notes that “Slaves in the Roman Empire were vulnerable to physical control, coercion, and abuse in settings as public as the auction block and as private as the bedroom” (p. 9).
Commentators on Philemon quite regularly cite Stoic writers, especially Seneca, to indicate that the equality of all humanity was a common notion in the ancient world. In his 47th letter to Luciliu, Seneca writes at length about the treatment of slaves, delineating the elements of the model master-slave relationship according to Stoicism: “Kindly remember that he whom you call your slave sprang from the same stock, is smiled upon by the same skies, and on equal terms with yourself breathes, lives and dies.” Later, he writes that, “all men, if traced back to their original source spring from the gods.”
But Seneca’s moral exhortation has been misused by NT scholars. Rather than being representative of a widespread conviction, Seneca is exhorting abusive masters who aren’t living up to Stoic ideals. He is a noteworthy exception, not an instance of the commonly-held conviction that slaves shared the same humanity as their masters.
For Glancy, “Little evidence supports the contention that these philosophers represented or affected wider public perceptions of the institution of slavery. We cannot assume on the basis of their writings that their philosophical positions on the relative insignificance of legally defined bondage or freedom affected their actual treatment of slaves they encountered or owned, much less that they influenced others to follow either their counsel or their example” (p. 7).
Now, we must keep in mind that there were different sorts of slaves in the ancient world—menial slaves, those who worked the mines, and others who worked in the fields were treated with contempt. There were also skilled laborers and even slaves who were trained as cooks, shopkeepers, artists, magicians, poets, teachers, and philosophers. And we simply don’t know what sort of slave Onesimus was, nor whether he was born a slave or became one at some later point. It may be that his name, which means “useful,” points to his being a menial slave, but this is only speculation.
Much more could be said here, but my point is simply this: Because the assumption was widespread that slaves did not share the same humanity as those born free, or certainly with their masters, it is unlikely that Paul’s expression adelphon en sarki can mean “fellow human.”