Boston Modern Orchestra Project: Child Alice

At Jordan Hall, March 25 at 8 p.m. Free admission, reservations required. www.bmop.org

“I always think people have a secret music,’’ said the composer David Del Tredici during a recent phone conversation from his home in New York, “a music which they love to do or write, which they don’t think counts.’’

Del Tredici, born in 1937, enjoyed composing in the freely atonal style that emerged early in the 20th century, and during the first decades of his career wrote some important music in that vein. But at some point, almost involuntarily, he realized that his “secret music’’ was based in tonality: the system of major and minor keys that underpinned a few centuries of music before him. Now, writing tonal music seems like no big deal. But when Del Tredici and a few others — most notably George Rochberg — moved in the 1970s toward what became known as neo-Romanticism, it was something of a scandal.

One summit of the movement is “Child Alice,’’ a sprawling two-hour setting for orchestra and amplified soprano of Lewis Carroll’s prefatory poems to “Alice’s Adventures in Wonderland’’ and “Through the Looking-Glass, and What Alice Found There.’’ It is the largest of Del Tredici’s several Carroll-inspired works.

Though it was conceived and written as a single two-part work in the early 1980s, “Child Alice’’ was parceled out and performed in sections to fulfill various commissions. Shockingly for a work of its stature, it has had only one complete performance, at Carnegie Hall in 1986. Its second will happen on Friday, in a free performance by the Boston Modern Orchestra Project under the direction of Gil Rose. (The ensemble has started a Kickstarter campaign to fund a recording.)

“?‘Child Alice’ is one of those pieces that comes along every once in a while and shatters the mold,’’ wrote Rose in an e-mail. “In music history this has been done for the most part by expanding or rejecting tonality. ‘Child Alice’ broke a trend by embracing it as the central issue to be dealt with. It is a piece that wears many disguises in broad daylight. It appears simple but is complex both musically and psychologically.’’

For himself, Del Tredici said that he thinks of “Child Alice’’ as “the last gasp of tonality in its really glorified state’’ — meaning that a sequence of keys and tonal centers underpins the entire structure of the piece, rather than being used simply as a coloring device, something more common and less remarkable, he said.

“The great glory of tonality was that it allowed us to hold things together over a long period of time, keep them interesting and moving,’’ he said. “It’s taken a long time to substitute for that most sophisticated of musical devices.’’ Mahler, especially the long final song of his “Das Lied von der Erde,’’ was an inspiration during the writing of “Child Alice.’’ So was Berlioz.

“Whenever you do something weird, you always look for precedents to support you,’’ Del Tredici said. “You want some friend to hold your hand.’’

Perhaps the most striking feature of “Child Alice’’ is that Del Tredici created a huge musical edifice for just two brief texts, neither of them part of the Alice stories proper. The poems, he said, seized his imagination because they evoked “my own sense of regret and ecstasy and childhood come and gone. They sort of tell the true underlying feeling of the story.

“You never set out to write ‘Child Alice,’’’ he continued. “One does not set out to do that. They began as little short pieces, and then for some reason they continued to grow. I’d find a new way to do this, another way to do that. I sort of had to put it all together, like a mosaic, from all these fragments. I wasn’t sure what the actual picture was going to be. But when it came out to being that size, I was horrified.’’ (He seemed largely serious about this last statement.)

Size wasn’t the only surprise; indeed, most of Del Tredici’s compositional choices seem almost involuntary, a matter of instinct instead of conscious decision. The shift toward tonality, he said, was also that way: not a crusading statement about aesthetics, but an intuitive response to the emotions Carroll’s writing unlocked. “Carroll was wit, whimsy, Victorian,’’ he explained, “and needed, I felt, a different kind of language. And so I gradually, without thinking, went to the tonal chords. They just seemed to fit the mood.’’

The first part of “Child Alice’’ is dominated by an innocuous little tune that threads its way through the entire movement, repeatedly changing character. Del Tredici admitted that his focus on this melody was “obsessive.’’ Asked why he was so fixated on it, he had no explanation.

“I don’t know why I stuck to that one tune,’’ he said. “I didn’t do that consciously. It just happened — [it was] what came out of me.’’ He paused, then continued. “One of the thrills [of composing] is wondering what’s inside you. Then it starts to come out.’’

Boston Modern Orchestra Project: Child Alice

At Jordan Hall, March 25 at 8 p.m. Free admission, reservations required. www.bmop.org

David Weininger can be reached at globeclassicalnotes@gmail.com. Follow him on Twitter @davidgweininger.