Directed by Daniel Sullivan, who was responsible for the award-winning Off Broadway productions of the play, the film has not quite shaken off its theatrical origins: it bogs down occasionally in staginess and facile sentiment. But when it remains true to the mordant grace of the writing and to the incandescent performances of the cast (Ron Rifkin in particular deserved some recognition from the Motion Picture Academy), Substance rages with heat and light.

Language certainly demonstrates its capacity for destruction when wielded by Isaac Geldhart (Rifkin). The child of the opening scene, he grows up into a thornily scrupulous publisher, a venomous martinet whose standards of aesthetic purity and caustic verbal brilliance he brandishes like a lash at those who love and work with him -- not least his three variously benighted children. Martin (Timothy Hutton), the eldest, is a Rhodes scholar who teaches landscape design at Vassar (his first appearance in the film, gazing with his blissed-out students at a stretch of pastoral splendor while new-agey music chimes on the soundtrack, is one of the film's sappier moments). Like his father, Martin is a survivor -- he's in remission from Hodgkin's disease. Perhaps because of that kinship, or because Martin refuses to get involved in his father's publishing company, Isaac dismisses his son as "the gardener -- Johnny Appleseed of the Hudson."

Isaac's contempt for his other two children is more casual and condescending. Sarah (Sarah Jessica Parker), "the bimbo," performs insipid songs on a children's TV show. Aaron (Tony Goldwyn), "the accountant", is the only one of Isaac's children who deigns to work for the formidable patriarch. It is, in part, an act of charity, as Isaac's publishing house of Kreeger/Geldhart has declined in fortunes precipitously since the death of his wife.

Dedicated to such "serious" (or as a potential Japanese investor puts it, "morbid") books as Water on Fire: An Oral History of the Children of Hiroshima and The Burning Sky: Art from the Spanish Civil War, the company needs a bestseller fast. Aaron, who's gay, is pushing his lover's slick and sexy novel. Isaac deems the book "crapola"; he wants to stake everything on an elaborate limited edition of a four-volume account of Nazi medical experiments. The conflict assumes Lear-like proportions as Aaron's siblings -- both shareholders in the company -- throw in with their brother. In a rage Isaac forms his own company and excommunicates his family, descending into Olympian failure and madness.

Portrayed by a lesser artist, Isaac would be impossible to embrace; he'd seem a mere "hateful prick," as Sarah puts it after an especially grotesque display of mean-spiritedness. Or as Aaron says, after a shockingly brutal altercation, Isaac would seem to deserve everything that's happening to him. But Rivkin does not allow you to forget he was that child at the beginning reaching out to grasp the rising ashes that are all that's left of his family. More important, he draws you into an insidious realm of desperate pain and vanity that seems to permit any outrage. Even when his "episodes" begin and he's arrested for too obsessively coveting a stranger's footwear, Rifkin's Isaac maintains an acid, elegant propriety. When interviewed by a social worker in a competency hearing, he pretends that she's a representative from Sotheby's evaluating his collection of memorabilia; his mixture of canniness and devastation as he relates the finer points of a postcard painted by Hitler is almost Promethean in its impact.

So it's a bit of a letdown when Baitz and Sullivan take the easy way out and wax melodramatic at the end, undermining the uncompromising vindication of language and family and all their attendant glories and abuses that had come before. No matter: the ear and vision of the work remain intact; its substance and fire prevail.