Ian Bostridge performed “Winterreise,” a song cycle for voice and piano by Franz Schubert, at the Library of Congress. (Simon Fowler)

Ian Bostridge is not a classical singer. Yes, he’s a tenor, and what he does is vocal performance, and it’s strikingly compelling. But classical singers produce sound in a certain way, with a certain kind of vocal support and certain accepted wisdoms about sound and line and diction. Bostridge, by contrast, comes at singing from entirely his own direction and arrives at his own unique conclusions and results.

Nowhere is this more evident than in Schubert’s “Winterreise” (Winter Journey), a song cycle that has been a hallmark for much of his career, and that he performed at the Library of Congress on Saturday afternoon. Bostridge, who holds a Ph.D from Oxford and is a published academic author (his dissertation was on witchcraft), has just brought out a thick and elegant book called “Schubert’s Winter Journey: Anatomy of an Obsession” (Knopf) about this cycle’s songs, poetry, historical and social context, performance, and a host of other tangential and illuminating topics in what is, in effect, the ultimate 528-page program note.

But although it may be unusual for singers to write long, intelligent books about music, it is not unique. What’s unique is Bostridge’s voice. It’s the sound of a grown choirboy: high and straight, with a quality of reediness in some notes and the ability to shade into an eerie half-falsetto before dropping, startlingly, into dark baritonal depths. Bostridge has a considerable vocal technique to be able to sing “Winterreise’s” 24 songs and show no more strain in the last song (“Der Leiermann,” the organ-grinder) than the first (“Gute Nacht,” good night). But his singing comes from his head, in more ways than one. Hearing it, you sense that rather than being supported from the diaphragm, it is controlled from above, on invisible marionette strings, one effect succeeding another as products of an active, slightly gothic imagination, not always entirely connected to his skinny body as it gyrates nervously around the piano.

The result, on Saturday, was an intriguing, often unnerving, often powerful performance. Sometimes, drama is an organic byproduct of the way an artist sings. In Bostridge’s case, it proceeds from ideas sequentially applied to the music, down to and including his clipped, precise German diction, offered as if he were not so much speaking the language as dissecting it.

This led to some startling juxtapositions when one mood was abruptly contrasted with another, as if Bostridge were speaking in tongues, leaping from character to character. More than once I thought of the early Schubert song “Erlkönig” (Erl King), not a part of “Winterreise,” which calls on the singer to take on three different voices. Bostridge seemed to offer several characters on Saturday: You could hear the gruff father in the low-pitched second verse of “Gefror’ne Tränen” (Frozen Tears), while the ghastly, malign, otherworldly lure of the Erl King was audible in, of all places, “Der Lindenbaum” (the linden tree), the most famous song of the cycle, in which the tree promises a specious peace, in the form of death, to the weary traveler.

To my ear, Bostridge’s performance was tantamount to someone offering a lecture-analysis of the work, pointing out a detailed spectrum of emotions and showing the ways it could or should go, from a kind of pantomime of drunkenness in “Erstarrung” (Stiffness/Freezing) to the artlessness of “Täuschung” (Delusion), which fell from his lips like a pressed flower petal, sweet and light and dead. Very seldom, though, did he seem to me actually to inhabit the piece himself — despite moments of acute observation. (In the 20th song, “Der Wegweiser,” the lonely traveler observes that he hasn’t done anything that should make him hide from the world, and Bostridge imbued the phrase with a poignant wistfulness that underlined the idea of a depressed person contemplating stepping out of his bleak reality and rejoining humanity — an idea that seems so simple, and yet is so impossible.)

His idiosyncratic vocal technique sometimes made him work harder than he had to. Bostridge doesn’t really have full-throated operatic beauty in his arsenal, as he revealed in the loud cries of “Mein Herz!” (my heart!) at the end of “Die Post” (The Post) the 13th song, which failed to make their effect; what he could do, when he sang loudly, was offer a chilling, almost inhuman fortissimo at the end of “Letzte Hoffnung” (Last Hope), the 16th song, which sliced like a metal blade. His spotty delivery, though — patches of staccato, near-yelling, a sudden eruption into a more fluid vocal line for a few notes — sometimes led to surprisingly avoidable mistakes, such as singing flat, repeatedly, as he worked to connect one note to another.

The pianist Julius Drake was both a remarkable partner and a striking contrast: attuned to every nuance of Bostridge’s delivery and playing off it with a more straightforward dramatic energy. His piano, like Bostridge’s voice, sprang from one character to another: jarring dissonances when the cock’s crow interrupts a happy reverie in “Frühlingstraum” (Dream of Spring), a dark thrumming beneath the spindly voice of a hurdy-gurdy in the final “Der Leiermann,” which sums up the cycle with a grisly portrayal of music offered as an inadequate, unheeded presence in a wintry world.

I suspect that most of the people in Saturday’s audience liked the performance more than I did. And I certainly found the afternoon involving, and sometimes illuminating. It’s often said, when text is set to music, that speech is striving to find song. In Bostridge’s performance, it was as if he were constantly striving, through the music, to find a way to speech — to articulate, through a challenging medium, exactly what it was that he meant. And perhaps that very frustration, the sense of struggle, was an integral key to his performance — all the way through to the nihilism of the end of “Der Leiermann,” which offered not even the satisfaction of a climax: dying away, instead, into the dull finality of nothing.