AS an artist Sean O'Faolain has the good fortune to be obsessed by a single idea. Readers of "Midsummer Night's Madness" will recall how the formally unrelated short stories in that book all elaborated a central theme; the change--usually a disintegrating change--wrought upon its characters by the stress of a hopeless political revolt. In "A Nest of Simple Folk" the pattern of a family chronicle extending in time from 1854 to 1906 is woven about a similar theme. By tracing the fortunes of three generations of Irish men and women, Mr. O'Faolain has been able to realize the implications of his subject to the full, and heighten its significance against a background not of revolutionary violence merely, but of long-drawn social decay.

A decade of scheming by Julie O'Donnell brought her youngest son not only the small holdings of his father, but the name and run-down estate of her sisters as well. Instead of working his property, Leo Fox-Donell spent his time tippling and wenching. More through inertia than patriotism he drifted into a secret political society and organized a raid on a police garrison. It failed when he stopped for a drink with his men before going to the ambush. He was still drinking when the police took him in. During his years in an English prison Leo lost the last of his holdings to an older brother and acquired instead a personal hatred of England. The rest of his life in a small town and in the city of Cork was spent in organizing spasmodic, futile revolts. His nephew, Johnny Hussey, who had risen in the world by becoming a policeman, sent him to prison again for trying to ship arms into the country. But before he died old Leo had the satisfaction of seeing Johnny's young son Dennis denounce his father for a spy and join the Sinn Fein during the Easter Rising.

"A Nest of Simple Folk" is as carefully studied as a novel could well be. Almost every relevant aspect of Irish life is built about the brief scaffolding of a plot outlined above. The book as a whole reminds one forcibly of the fortunate position which the Irish writer enjoys. Sean O'Faolain belongs to a culture which has felt intensely the impact or modern social unheavals, and simultaneously enjoyed the revival of rich and ancient national culture. As an artist he has profited by the great achievement of James Joyce in creating a mature racial conscience, while as an individual he is closer to the soil than Joyce ever was. The stripped and ungainly realism frequent in contemporary novels is not forced on a man with such a background. "A Nest of Simple Folk" is a profound and beautifully written book in itself, and leaves one with the expectation of even finer things to be written by its author.