Apparently unable to choose between writing a comprehensive country-by-country survey of 20th-century opera or an argumentative think-book, Mordden attempts to do both at once--with sometimes impressive but often dissonant results: the arguing undermines the organization and authority of the survey; the survey's demands on space and shape leave the argument fragmented and underdeveloped. Mordden's principal thesis is that modern opera irreverently mixes the art's two historically distinct strains--sacred (zenithing with Wagner) and profane (opera buffa, etc.)--into something ""bimodal,"" like ""satiric tragedy,"" as myth emerges with legal primitif. He can certainly sing this strain to the music of Alban Berg, or Ravel, or Richard Strauss perhaps--or even some of Turandot (which he surely overpraises). But since surveyor Mordden also must discuss folk opera and Menotti and Poulenc's Dialogues and Britten (Peter Grimes satiric? No way), he spends much of his time carving out exceptions to an overreaching rule. Far more generally applicable--if less provocative--is Mordden's characterization of modern opera as a return to ""the Word"" after a century of text-starved, text-slurred romanticism. But neither of these stagily presented theses (and certainly not Mordden's forecast of a Godot-absurdist future for opera) can compete with the real strength of this book: the lively, sneakily informative opera-by-opera, composer-by-composer appreciations, which show Mordden to be far more eclectic in his devotions than his pro-avant-garde formulas would suggest. From Louise (1900) to Lily (1977), he zestfully captures the musico-dramatic essence of all the major works--and dozens of comparative obscurities. Admittedly, this zest too often pushes Mordden beyond felicitous phrasing over into the fey and the flip (nationalism is ""more virile than vegetarianism, nicer than sadism""). But, even if such lapses and an unfulfilled doctrinaire design keep this from being a solid-sure chunk of reference, it offers vivid evidence of modern opera's variety--and of one listener's contagious enthusiasm for it.