What defines an extended family? Blood ties? Common interests? Mutual dependence? Mere proximity? Or is it the need or desire to take responsibility for other people, however reprehensibly they’ve behaved in the past?

Matthew Lopez’s play “The Whipping Man” asks those questions about three men reunited after the Civil War in Richmond, Va.– and, like most good theater, does not provide simple answers.

Their relationship has changed in ways they haven’t yet fully realized. Former slaves Simon (John W. Price) and John (Jeremy DeCarlos) used to be owned by the family whose son Caleb (Brett Gentile) has come home, his body blasted by a battle wound and his mind clouded by pain. Do they owe him loyalty, or does freedom brought by the Emancipation Proclamation give them the right to leave with clear consciences?

The three are tied, in an unusual but literal sense, by blood. The title refers to an independent contractor who punished the slaves of landowners who didn’t have the time or inclination to wield a whip themselves; all three characters have had a pernicious connection with this whipping man. Lopez wants us to consider whether we can be whole people without forgiving cruelties of the past.

His play revives memories of another work with a “superior” white character and two black men, one older and one younger, who explore new attitudes toward him. “Master Harold...and the Boys,” Athol Fugard’s 1982 broadside against South African apartheid, treads similar ground.

What makes Lopez’ script unique is that its three characters do share a potent bond, whether they want to or not: They’re Jews, due to celebrate Passover together during the action of the play. Caleb was apparently born a Jew; Simon and John adopted the religion, perhaps at their master’s behest. So they make up a “family” of another kind, one whose members are obligated not to neglect their fellows.

Lopez salts the play with revelations and spaces them out neatly. Some leap out abruptly, and some dawn on us gradually: We see the parallel between the ex-slaves’ situation and Israel’s deliverance from bondage in Egypt, when the Jews also had an uncertain future before them. (I wish someone had helped the actors more with Hebrew pronunciation, though.)

We’re in good hands as soon as Hallie Gray’s evocative and spooky lighting comes up on Dee Blackburn’s set, a once-handsome house shattered by fire and shelling.

DeCarlos and Gentile give performances we haven’t often seen from them: the former mercurial and sly, the latter hangdog and haunted. John’s a trickster, trying to bluster his way through an uncertain time; Caleb’s a self-deluder, trying to believe he could have a relationship of equality and affection with a human being his family owns.

Price lived through the Civil Rights Era and remembers a segregated America. Perhaps his memories inspired a performance of stubborn, quiet strength: Simon helps Caleb but continually, patiently explains how the household dynamic is different now.

Simon also reminds us that freedom means not only independence but choices. Some of those unite us, and some divide us. Some make us stronger; some make us weak. But the free man who stands utterly alone handicaps himself from the start.