Twenty minutes into Nina Raine's play, I put something in my notebook that seemed insightful at the time. I wrote that this is the first English non-Jewish family I have seen on stage who argue like Jews.
Which is not to say that all Jewish families argue like the family depicted in Raine's play, like hyenas over a carcass. But it is to say that the kind of family that communicate in no-holds-barred rows; have a quasi-Asberger's disregard for the feelings of those they love most, and constantly probe for the weakness in every sentence, invariably, that family is Jewish.
The ferocious argument, superbly staged around a dining table by director Roger Michell, is a way of expressing love. The odd one out is Billy (Jacob Casseldine), the deaf student son. Though he is more loved than anyone, in a family that defines itself through verbal battling, he is inevitably sidelined.
Raine gained a reputation for writing great dialogue with her first play, Rabbit. With Tribes, she confirms it. The exchanges are exhilarating, closely observed and cutting, even if the drama on which they are based sometimes feels merely like a vehicle for the dialogue.
Here, the don't-give-an-inch quarrels are not about who does the washing-up but about whether each family member's opinion, whether on art or politics, can stand up to the ruthless scrutiny of everyone else around the table.
Take the exchange driven by Christopher (Stanley Townsend), the foul-mouthed father and academic who attacks cliché and conformity wherever he finds it. He is appalled to learn that Billy is learning to sign from his new girlfriend, Sylvia (Michelle Terry).
Billy has been deliberately brought up not to learn sign language. To sign, he would have to join the deaf community, goes Christopher's argument, and to join the deaf community is to conform to a group that bases its identity on persecution. "The deaf! The f*****g Muslims of the handicapped world," says Christopher, before declaring that sign language constructs personas based on the kind of fake joviality that he also detects in northern people.
It is here that Daniel (Harry Treadaway), the other son, jokes that he thought sign language was Jewish, not northern. He illustrates his point with a bit of grotesque gesticulation. "I'm allowed," he adds, "we're Jewish."
At this point, I crossed out my note.
The question posed by Raine's play explores the extent to which identity is forged and hijacked by the groups we join and the families to whom we belong. And it does so in a thrillingly articulate and sometimes shocking way. But when Billy opts out of the family and into a community of fellow deaf people, the play begins to feel less dangerous and more like the kind of drama in which liberal, atheistic parents find to their horror that they have a religious son.
Still, Raine's writing is so intelligent, even well- trodden territory feels virgin. And she finds inventive ways to examine her themes. When Billy and Sylvia use (surtitled) sign language to communicate, the rest of the family find themselves in the position in which Billy has lived all his life.
And in one quiet, immensely poignant moment, a play populated by shouters gives over to a speechless exchange between Billy and brother Daniel, with everything contained in an exchanged look.
It is also worth noting that after the un-PC racial politics expressed in its recent production, Clybourne Park, the Royal Court is becoming the theatre where the unsayable is said.
(Tel: 020 7565 5000)