Instead of offering another biographic gloss of Yeats's poetry, historian Foster (Irish History/Oxford; Paddy and Mr. Punch, 1994, etc.) concentrates on the young poet's many personae: journalist, revolutionary, playwright, political figure, and occult experimenter. Foster's detail-weighted, date-ballasted tome sets itself in contrast to previous biographies, such as Richard Ellmann's elegant and compact Yeats: The Man and the Masks. The Apprentice Mage is an episodic serial of the poet's diverse activities up to his 50th year, concentrating on action rather than on art. If Yeats inherited his volubly aesthetic nature from his bohemian father, John Butler, he was grounded in Ireland on his mother's side (the dourly mercantile Protestant Pollexfens). Foster sees the Pollexfens as the source of Yeats's problems with Anglo-Irish politics. His exile with his family in London gets some credit for stimulating his fledgling talents. Foster does a good job of tracking the young man's footloose intellectual rovings in the 1890s, from the British Museum to the decadent Rhymers club and his dabblings with the Golden Dawn, an occult society. But his analysis of character seems rather rudimentary: The author baldly states that Yeats's early career was shaped by ""sexual frustration"" and ""personal ambition,"" and that's about as much psychological insight as he provides. If Foster never really grasps his subject's mercurial personality, to say nothing of his poetry, at least he never falls under its spell as he charts Yeats's political progress from Fenian fellow traveler at the beginning of the Celtic Twilight to his Home Rule Liberalism in the face of the Sinn FÃ¢in generation. He maintains a distanced objectivity even while describing some of Yeats's most passionate experiences, including his affair with Maud Gonne and his life at the Abbey Theater. This is the Pollexfen account of Yeats's life: dense with facts, skeptically commonsensical, but a bit obtuse in spirit.