One synonym for the definitive biography is dull; another is dutiful. The biographer is obliged to deal with every aspect of his subject’s life and work, and the result can be an ill-proportioned account lacking highlights, a sense of discrimination, or drama. Such tomes become useful reference works but also indigestible narratives.

W.A. Speck’s subtitle for “Robert Southey” (Yale University Press, 306 pages, $45) might have been “an entire biography of an entire man of letters.” Since Robert Southey was a poet, novelist, historian, biographer, book reviewer, and playwright, he justified the sobriquet Byron bestowed on him. Actually, however, Southey’s greatest achievement, as Mr. Speck vouchsafes in the last two pages of his biography, is as a letter writer.

How odd and puzzling it is that the biographer should hold back this claim until the very end of his book, and how disappointing that he does not make better use of his subject’s correspondence. Mr. Speck quotes one Southey critic, “There he stands, to the life, independent, irritable, generous, tender, kind-hearted, loyal — above all, intensely human.” Mr. Speck quotes Southey repeatedly, but not to such good effect: Rarely does his subject seem as alive as that one critic suggested.

The trouble is that Mr. Speck drowns out his subject with so much diurnal reporting. This day-to-day kind of biography blows apart any effort to come to terms with Southey’s significance. Thus, for example, Mr. Speck announces on page 137 that Southey, a prodigious book reviewer, disparaged five lives of the Admiral in the “Quarterly Review,” prompting the publisher John Murray to propose that Southey do the job himself.

But why did Southey dismiss these other books? Instead of providing an explanation, the next 15 pages follow the calendar of Southey’s life before halting for a two-page account of the Nelson biography Southey finally got around to writing. From there follows a paltry portrayal of what is undoubtedly Southey’s most significant individual work. No one reads his tedious booklength poetic epics; at best he is remembered as one of the Lakers who befriended Coleridge and Wordsworth.

Of the Nelson biography, Mr. Speck observes: “However overdone it might have seemed, Southey’s was to become the definitive biography for its generation, and one that is still in print today.” Why? He does not say, even though it is rare for a biography to remain in print for so long, and even though subsequent biographers have paid tribute to Southey.

Instead, Mr. Speck quotes Southey’s “purple passage on Nelson’s death at Trafalgar”:

The most triumphant death is that of the martyr; and the most awful that of the martyred patriot; the most splendid that of the hero in the hour of victory; and if the chariot and the horses of fire had been vouchsafed for Nelson’s translation, he could scarcely have departed in a brighter blaze of glory.

The passage may indeed be purple, but this is how many Englishmen regarded Nelson’s death, and it is a piece with Nelson himself, who penned his own purple passages in letters and clearly saw himself as a worthy successor to the heroes of ancient Greece and Rome. Southey voiced a nation’s sentiments, not only his own. And for a biographer to simply call Southey’s words purple is to display an ignorance of historical context and of the kind of biography Southey was writing.

Southey’s cadenced prose was memorable — indeed easily memorized by generations of Englishmen and -women.And though Southey was chary of describing Nelson’s affair with Emma Hamilton, that he did so at all sets him apart from the Victorian biographers who would soon embalm their subjects in euphemistic prose.

Discussion of the Nelson biography should have been one of the big moments in this book. Mr. Speck does not even comment on the fact that Southey (a young radical who supported the French Revolution and planned to join Coleridge in an American commune that would pursue a quasi-socialist form of government they called “Pantisocracy”) employed narratives such as his biography of Nelson to move toward a much more conservative and nationalistic position.

If Mr. Speck does little to shape his narrative into dramatic units, he can often encapsulate an episode or theme in his subject’s life with superb economy. Thus he describes Southey’s attraction to Mary Barker, who apparently was a much more lively coadjutor than Southey’s own wife Edith:

There is certainly a sexual tension in Southey’s letters to Mary Barker that cannot have been unintentional. ‘I look upon novel reading as being exactly to the mind what rank debauchery is to the body,’ he once observed to her, ‘over stimulation instead of true delight.’ At the same time, those letters he wrote to both Mary and Edith tell them what he wanted them to know. He seems to have been trying to control a situation he himself was afraid might get out of hand.

This seems admirable in a biography: succinct attention to the nuances and subtext of evidence without unduly pressing a case that cannot be proved. The trouble, then, is not Mr. Speck’s writing — at least not sentence by sentence — but rather that he so often lacks a sense of timing and pace. His book is not too long; instead he ought to have had an editor who would suggest, “Cut here, expand there, and for God’s sake, build toward those crucial moments in Southey’s life.” Southey could sparkle, but alas he has been saddled with an all too plodding biographer.

crollyson@nysun.com