Just as Wagner’s “Tristan und Isolde” is the most sexually explicit opera in the classical repertory — mothers at the end of the 19th century wouldn’t allow their daughters to listen to its “love duet,” let alone the ecstatic “Liebestod” — so Franz Schubert’s “Winterreise” is the greatest, and the most bleakly melancholy, of all song cycles. In a series of sung soliloquies (with piano accompaniment), a young man recalls how he was compelled to leave his beloved, wander forlornly into the mountains and gradually resign himself to death.

Based on 24 poems by Wilhelm Müller, this desolate “winter journey” was composed at the end of Schubert’s short life: He died at age 31 in 1828, almost certainly because of syphilis. Nonetheless, during an active career of only 15 years, the chubby Austrian managed to compose more than 600 songs, among them such audience favorites as “The Erl King” and “Gretchen at the Spinning Wheel.” As a genius, he could produce as many as eight songs in a single day (and did so on Oct. 15, 1815). Little wonder the Graham Johnson edition of the complete lieder runs to an imposing 37 CDs. Yet Schubert’s oeuvre also includes symphonies, church music, exquisite piano trios (the second movement of the B-flat trio is the very definition of “achingly beautiful”) and much else.

“Winterreise” itself has been recorded by scores of singers, at least five times by baritone Dietrich Fischer-Dieskau. But it has also been sung by the mezzo-soprano Brigitte Fassbaender, bass-baritones Hans Hotter and Bryn Terfel and, outstandingly, by several tenors, including Peter Pears and Ian Bostridge. In “Schubert’s Winter Journey”— an appropriately small but elegant volume in a starkly white dust jacket — Bostridge reflects on what he’s learned after 30 years of studying and performing Schubert’s masterpiece.

The book’s subtitle, “Anatomy of an Obsession,” nods to Robert Burton’s “The Anatomy of Melancholy,” so it’s no surprise that Bostridge is similarly digressive, learned and idiosyncratic. For starters, he mentions that he has never studied music at any university or conservatory. In fact, he’s a lapsed historian and, by the evidence of these pages, one who still likes to ply his old trade. For his interpretations of this “first and greatest of concept albums,” the singer-scholar ropes in philosopher Jean Jacques Rousseau, novelist James Fenimore Cooper and painter Caspar David Friedrich, as well as Jack Kerouac, Bob Dylan and Samuel Beckett.

In his journey through “Winterreise,” he explains the formation of snow crystals and glaciers, the mythology of the horn in Teutonic culture, the sociological impact of faster and more efficient mail coaches, the standard mercury treatment for syphilis, German political thought in the post-Napoleonic era and, inevitably, the alienation of modern man. We are reminded that Schubert’s teacher was none other than court-composer Salieri, the legendary rival of Mozart, and that Schubert himself was one of the torch-bearers at the funeral of Beethoven.

”Schubert's Winter Journey: Anatomy of an Obsession.” (Knopf)

Bostridge begins each chapter with one of Müller’s German poems and his own facing-page English translation. He examines more closely what the lyrics actually say, then relates them to the historical moment and milieu. With learned ease, he compares the songs’ unnamed wanderer to Byron’s moody heroes, traces the symbolism of crows in Western art, points out that Müller translated Christopher Marlowe’s “Dr. Faustus” into German, and cites maverick philosopher Slavoj Zizek’s observation that Napoleon’s disastrous invasion of Russia was a “gigantic ‘Winterreise.’ ” In the chapter about the song “On the River,” Bostridge even reproduces graphs detailing the temperatures of the Little Ice Age of 1350 to 1850.

When, in “Rest,” the wanderer seeks refuge in a peasant’s hut, Bostridge disingenuously asks, why is it a charcoal burner’s hut rather than, say, a shepherd’s? He soon proceeds to explain that by the early 19th century, charcoal burners were losing their livelihoods because the age’s dark satanic mills were increasingly powered by coke. The traditional charcoal burner is thus a poster boy for the human cost of industrialism. Yet that’s not all. As Bostridge reminds us, members of a contemporary Italian secret society, much feared by the Habsburgs, were known as the ‘Carbonari,’ i.e., charcoal burners. This singer-scholar clearly knows his Marx as well as his musicology and throughout underscores the subtle political implications of what may seem like merely romantic effusions. On one page, he even refers to Schubert as “bolshie.”

In explicating the cycle’s most famous song, “Der Lindenbaum,” Bostridge dramatically steps up his razzle-dazzle in an extended essay on the cultural significance of the linden tree. “As far back as Homer, the linden had been a magical tree.” German elders governed from under the linden. In “The Sorrows of Young Werther,” Goethe’s bittersweet tale of unrequited love, the tree is used throughout as an erotic leitmotif. Thomas Mann’s “The Magic Mountain” ends with its confused hero, now an infantry soldier in World War I, singing this very song as he rushes over the top toward almost certain death. Even Proust’s narrator dips his madeleine into an infusion made from the tree’s flowers. The linden is, in short, a potent symbol of love, death and memory.

While Bostridge obviously delights in historical investigation, he also enjoys conveying insights from vocal performance. “In song recitals, as opposed to opera — where a wall of light can separate the actor from the auditorium — the audience are usually visible, part of the performing equation, to play with and against.” Operatic tenors call high B’s and C’s the “money notes.” Bostridge even refers to the piano part in one Schubert song as “insincere Romantic flummery.”

Throughout, he muses on the character of the unnamed wanderer: “Do we identify with him, or seek to separate ourselves from him? Is he sympathetic or repellent? Insightful or embarrassing? Weird? Normal? These discomfiting responses are what make ‘Winterreise’ so compelling.”

Of the last song of the cycle, “The Hurdy-Gurdy Man,” Bostridge writes that it is “one of those magical, totemic pieces of music which seem to have a power and a resonance beyond all rational explanation.” An aged hurdy-gurdy man mechanically cranks out trashy tunes even though no one puts any coins in his little plate. How poignant that one of the supreme composers of the Western world should end “Winterreise” with this pathetic beggar, at whom the dogs growl. Is the old man Death? Or is this how the dying Schubert saw himself? “Should I go with you?” asks the wanderer. “Will you to my songs/ Play your hurdy-gurdy?”

“Schubert’s Winter Journey” both deepens and contextualizes this emotionally somber masterpiece, the ideal music for darkest February. While reading, I also listened to him sing, and even though I grew up on Fischer-Dieskau’s baritone, I’m nearly persuaded that a light tenor voice is best for this still, sad music. But there’s no need to choose. Almost any recording of “Winterreise” will convey its lonesomeness and austere beauty. “Mein herz! Mein herz!”

Dirda reviews books for The Washington Post every Thursday.

Ian Bostridge will perform “Winterreise” and sign copies of his book at the Library of Congress at 2 p.m. Saturday.

SCHUBERT’S WINTER JOURNEY

Anatomy of an Obsession

By Ian Bostridge

Knopf. 502 pp. $29