“Winterreise” has done its work on the imagination and nerves of tenor Ian Bostridge, over a long period (Bostridge estimates that he has sung the cycle at least a hundred times), a passion distilled into “Schubert’s Winter Journey: Anatomy of an Obsession,” a diverting, deceptively digressive tour. Organized as 24 somewhat self-contained essays — each one exploring one of the cycle’s songs — Bostridge casts his net wide, from the literary significance of glaciers to the taxonomy of birds to Bob Dylan himself. The frost on the window in “Frühlingstraum” (“Spring Dream”) invites a scientific and poetic history of snowflakes and ice. “Gefrorne Tränen” (“Frozen Tears”) prompts a telling memory of a performance Bostridge gave in Moscow, which leads to a meditation on Napoleon’s invasion of Russia, the Nazi siege of Stalingrad, and the course of German nationalism. The common thread is classical music’s energetic paradox, a paradox the book embodies rather than explains: that art created in a very specific — and, often, very foreign — place and time can nevertheless meaningfully speak to an ever-different here and now.

How many roads must a man walk down? The narrator of “Winterreise” (“Winter Journey”), Franz Schubert’s 1827 song cycle on Wilhelm Müller’s poems, has had to leave home, walking through an increasingly frozen landscape. He is an archetypal Romantic hero: enigmatically afflicted (some sort of heartbreak is implied, but never elucidated), psychologically burdened, in self-aware thrall to his emotions. Insistently expressive but narratively opaque, “Winterreise” demands explanation even as it renders explanations mundane, a challenge that has compelled generation after generation of performers. (Dietrich Fischer-Dieskau, the work’s most celebrated 20th-century interpreter, recorded it no fewer than seven times.) Audiences, too: As pianist Charles Rosen once wrote, the cycle “does not work upon the listener’s imagination but upon his nerves.”


Much of Bostridge’s exploration comes from a performer’s perspective: cogent explanations of the niceties of musical notation and interpretation, close readings of the text. And much of it reflects back on Schubert himself, his friends, his milieu, the syphilis that darkened his final years and killed him at 31, the year after he wrote “Winterreise.” (Schubert corrected proofs of the cycle on his deathbed.) But the book also approaches from myriad scholarly and historical angles, vectors Bostridge — who trained as a historian — chooses with judicious flair. For “Die Post” (“The Mail”), Bostridge emphasizes the contemporary ironic contrast between the Romantically evocative hunting horns and the horn on the newfangled mail coach — a warning against hearing the song as cozy nostalgia. With “Rast” (“Rest”), he unpacks the meaning of the abandoned charcoal-burner’s hut where the traveler stops to rest, teasing out reference to the turbulent politics of the day, and both Müller’s and Schubert’s subtle, radical dissidence.

The cycle’s most famous song, “Der Lindenbaum” (“The Linden Tree”), prompts an especially wide-ranging mix of past and present: Renaissance botany, Romantic imagery, German nationalism, Thomas Mann, Marcel Proust. In Bostridge’s telling, such detail is not extra weight on the journey, but a wind at the back. Throughout, whether aiming from past to present or present to past, Bostridge is eager to expand the music’s possibilities, to expand the reach of its allusive web — so much so, that when Bostridge expresses skeptical exasperation over the relevance of the open question of Schubert’s sexuality (a major controversy in early 1990s musicological circles), it feels dissonant, a rare instance of a potential interpretive avenue being closed off, rather than opened up.


Far more often, Bostridge’s curiosity enriches the book and the music. Discussing the song “Mut” (“Courage”), with its defiantly cheerful denial of God, Bostridge joins the text, Schubert’s religious attitudes, and Schubert’s art under the banner of John Keats’s “negative capability,” that is, “capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason.” Bostridge himself reaches after fact, but out of a determination to honor the mysteries. The continuing power of “Winterreise,” a power the book idiosyncratically but effectively evokes, is to be found (or, as the case may be, not found) in the work’s multitudes, of moods, images, hidden answers, clear obscurities.


To fix such ambiguity in notation and then reconstitute it in performance is music’s great challenge, but also its great coup. Willa Cather left an artful suggestion of the duality in her 1935 novel “Lucy Gayheart.” Cather cites “Winterreise” early in the story: The title character, having traveled from Nebraska to Chicago to study piano, hears the cycle sung by Clement Sebastian, an older singer with whom she falls in love. Sebastian is killed on a journey abroad; Gayheart returns home. But, in a way, she has never left — as a girl of 13, she had run through fresh cement in front of her house, and the footprints remained, frozen in motion: “the print of the toes was deeper than the heel; the heel was very faint, as if that part of the living foot had just grazed the surface of the pavement.”


Lucy Gayheart herself dies, too young, falling through ice and drowning; many years later, Harry Gordon, the local banker who courted her, who spurned her, returns to the Gayheart house. Lucy’s teenage flight is still there, remembered in cement. Gordon pauses “mechanically on the sidewalk, as he had done so many thousand times, to look at the three light footprints, running away.” Such is “Winterreise”: a getaway captured, a preserved transience, even after countless revisits, still there and still fleeting.

Matthew Guerrieri is the author of “The First Four Notes: Beethoven’s Fifth and the Human Imagination” and writes frequently on music for The Boston Globe and NewMusicBox.