Oh, I see. This is August: Osage County with a big, fat master's degree. Perhaps a doctorate.

So it might seem, amid the hyper-intellectual verbal volleys among the prickly, literate characters who populate the first act of Tribes, the celebrated Nina Raine play that opened at the Philadelphia Theatre Company Wednesday after successful runs in London and New York. The setting is a modern, writer-dominated British household with carelessly towering shelves of books and people who are so cerebral that they can't experience an emotion until they attach a word to it and can't fathom the damage they inflict amid armchair excoriations.

The damaged grown children keep boomeranging their way home in defeat, not knowing what to do with themselves, and being assured that their failed romances were with persons with "all the charisma of a bus shelter." The deaf son, though, never left - though he's about to.

Then comes Act II, in which what was previously a quirky dysfunctional family drama morphs into something much more powerful, investigating a seldom-voiced corner of deaf society and doing so in a way that the play acquires shocking universality. As the deaf son Billy accuses his family of life-long insensitivity, anyone who has been marginalized for what they are will also see their own selves onstage.

In other words, Tribes is one of the more unexpectedly powerful family dramas to arrive in recent years, and the Philadelphia Theatre Company production is the all-around equal to that which enjoyed an extended run at New York's Barrow Street Theatre.

The Philadelphia cast hasn't yet become the kind of well-oiled ensemble that keeps tedium from setting in during the first act. But all of the actors have their individual virtues - such as John Judd as the monster father and especially Alex Hoeffler's slow-building Daniel, the son with encroaching mental illness - amid director Stuart Carden's well-calculated emotional arc.

Of course, the core of any good  production of Tribes is the deaf son Billy, played here by the young Texas actor Tad Cooley in a one-of-a-kind performance, luminously innocent in the first act, showing how his character's deafness had saved him from the destructive onslaught of words. He dressed, moved, and reacted differently from the others - and rightly spoke with an accent unlike theirs. His Act II eruption was a flurry of angularity that beautifully registered not just his long-simmering rage but also a lack of typical filters. So was it any surprise that, with his new-found place in the world, the character goes power mad?

Much of Tribes doesn't add up, and that's among the play's great strengths, and appropriate to a play about the limitations of language. Many rash acts in the narrative can't be explained easily, which means that the viewer's primary sympathies are likely to change from one viewing to the next. What could be seen as a puzzling Act II resolution was, for me, a yin/yang balance that says no extremes, however much they might seem liberating, are viable over the long run. In a family that can't live with or without each other, they find a way to do both.


 Presented by Philadelphia Theatre Company through Feb. 23 at the Suzanne Roberts Theatre, Broad and Lombard Streets.

Tickets: $46-$59.

215-985-0420 or philadelphiatheatrecompany.org.