“Why do people have to like Wordsworth and hate Coleridge and vice versa?” asked the poet Edmund Blunden. Adam Sisman quotes this forlorn question at the beginning of “The Friendship” (Viking, 429 pages, $27.95), and it hovers plaintively over the saga of love, admiration, envy, and despair that follows. More than any other two poets in history, William Wordsworth and Samuel Taylor Coleridge were indispensable to each other. In the first intoxicated years of their intimacy, from 1797 to 1801, they lived side by side, wrote at the same desk, exchanged ideas, and plans, and lines of verse. Wordsworth moved to the Quantock Hills to live near Coleridge, then Coleridge moved to the Lake District to live near Wordsworth. “Lyrical Ballads,” the volume they published together in 1798, contained masterpieces by each poet: Coleridge’s “Rime of the Ancient Mariner” and Wordsworth’s “Tintern Abbey.”

But if the two poets helped each other to immortality, they also forced posterity to weigh them forever in a single balance. The world’s fascination with their friendship began early on. Idealistic young men like William Hazlitt and Thomas De Quincey revered it, while venomous Tory critics like Francis Jeffrey derided it. And when, as happens with almost all friendships, the two men’s divergent lives and fortunes caused them to grow apart, the world found the assignment of blame a fascinating pastime. Coleridge’s friends thought Wordsworth was exploitative and egotistical; Wordsworth’s friends considered Coleridge a weak-willed parasite. The final breach, when it came in 1810, could not have surprised either party, though it caused Coleridge at least intense grief: “a compressing and strangling Anguish,” he wrote in his notebook, “made up of Love, and Resentment, and Sorrow.”

After reading “The Friendship,” it is tempting to add to Blunden’s Law what might be named the Sisman Corollary: Biographers and reader of biography will be inclined to prefer Coleridge, while poets and lovers of poetry will tend to cast their lot with Wordsworth. Although Mr. Sisman does not write, like many students of the Romantic period, with any ideological parti pris, the nature of the available evidence, and the sheer narrative possibilities of the story, almost compel him to make Coleridge the hero of his book. It is the same logic that led Mr. Sisman in his last work, the delightful “Boswell’s Presumptuous Task” (2000), to put the flawed and often contemptible Boswell at center stage, rather than the eminent Dr. Johnson. For a storyteller in our anti-heroic age, the marginal and neurotic beat the authoritative and magisterial every time.

In Coleridge, Mr. Sisman has an anti-hero on an epic scale. Born in 1772, the youngest of 10 children, he was considered a prodigy from the start: By the age of 3, he was reading the Bible. But his cosseted childhood, he later came to believe, left him unfit for adult life.

Throughout his life, he would remain brilliant and lazy, forever coming up with grand schemes — an epic poem, a new philosophical system, a socialist colony, a history of Christianity, a weekly newspaper that he could not finish, or even start. Once he became an opium addict, his health and spirit were shattered, and even his friends stopped believing in his plans. Yet no one who ever knew Coleridge doubted his tremendous gifts. “It vexes & grieves me to the heart,” said the poet Robert Southey, “that when he is gone, as go he will, nobody will believe what a mind goes with him — how infinitely and tenthousand-thousand-fold the mightiest of his generation!”

If we do still believe in Coleridge’s powers, it is almost entirely thanks to what he achieved during the first years of his intimacy with Wordsworth. The meeting of the two poets was inevitable, given that they moved in the same politically radical circles. The best parts of “The Friendship,” in fact, are devoted to the social and intellectual milieu that nourished the friends and the friendship. Like Coleridge, if less vocally, the young Words-worth was a passionate supporter of the French Revolution, at a time when French radicalism was the great boogeyman of the English imagination. Unlike his friend, Wordsworth had actually lived a year in France at the height of the revolution, and he fell in love with a French woman named Annette Vallon and fathered an illegitimate daughter. Mr. Sisman charts the long arc of their radical generation, which can’t but remind us of the adventures of the American Communists of the 1930s or the New Left of the 1960s: from idealism through disillusionment to middle-aged respectability.

Thanks to their political connections, Wordsworth and Coleridge knew many people in common. Their first meeting took place in the fall of 1795 in Bristol, a manufacturing city that was a center of middleclass, Nonconformist, politically advanced thinking. “I saw but little of him,” Wordsworth complained. “I wished indeed to have seen more — his talent appears to me very great.” But the friendship really began in June 1797, when Coleridge came to visit William and his sister Dorothy at Racedown, Dorset. Three weeks later, when Coleridge had to go home to Nether Stowey Wordsworth went with him, and quickly found a house to rent in the neighborhood. During the next year, they would see each other almost daily and between them produce around 6,000 lines of poetry. It was one of the miraculous years of English poetry, and laid the foundation for the Romantic movement. Even in that first glorious year, however, the worm was in the apple. In 1798, Coleridge was far better known than Wordsworth: He had published more poetry, written pamphlets and articles on political subjects, and even had a brief career as a preacher. “By comparison,” Mr. Sisman writes, “Wordsworth was nobody.” Yet Coleridge felt a need to abase himself before the superior genius of Wordsworth. When a mutual friend, Thomas Poole, expressed some skepticism of Coleridge’s praise, he retorted: “What if you had known Milton at the age of 30, and believed all you now know of him?”

No one’s ego could sustain this subservience forever without paying a price. And as Wordsworth went from strength to strength — writing dozens of immortal poems, marrying the woman he loved, achieving fame and prosperity — Coleridge descended further into his spiral of addiction, writer’s block, and shame. The contrast ate away at his self-respect: “I never had the essentials of poetic Genius,” wrote the author of “Kubla Khan,” “but merely mistook a strong desire for original power.” Like an ostrich, “I cannot fly, yet have wings that give me the feeling of flight.”

Mr. Sisman tells this often-told story well, synthesizing original sources and recent scholarship into an appealing, informative book. Yet even he is forced to turn the story of “The Friendship” into the story of Coleridge’s friendship, leaving Wordsworth a rather remote, unresponsive, and therefore unattractive figure. It is important to remember that it was Wordsworth who produced so many wonderful poems, while his more fascinating friend was wallowing in empty schemes. Confidence and reticence almost always go along with artistic success, while doubt and loquacity are the properties of failure. If we find the latter qualities easier to write and read about than the former, it may be only a sign of our age’s discomfort with achieved greatness.

akirsch@nysun.com