First the good news: Jack Kerouac’s “lost” novel “The Sea Is My Brother” (Da Capo, $23) isn’t entirely unreadable. In fact, the book — written in 1943 when the author was 21 — is pretty good as far as Kerouac juvenilia goes.

That’s not saying much; his “Orpheus Emerged,” completed two years after “The Sea Is My Brother” and published in 2000 as an early generation e-book, is one of the worst pieces of narrative prose I’ve ever read. This is a conundrum when it comes to literary estates, perhaps none more so than Kerouac’s.

Still, taken together, along with the stories gathered in “Atop an Underwood” (1999), these beginning efforts raise an interesting if largely overlooked question: How did such a mannered young writer, self-indulgent and often woefully pretentious, become the purveyor of his own uniquely American idiom, jazz-inflected, improvisational, a “spontaneous bop prosody”? That, as much as anything, captured the scattered sensibility of the United States in the 1950s, a nation frantically searching for some guise of normalcy beneath the fracturing shadows cast by the atomic bomb.

That’s no mere hyperbole. Like their contemporaries the beboppers and the abstract expressionists, Kerouac and his Beat compatriots Allen Ginsberg, Gregory Corso and William S. Burroughs were responding to the fragmentation unleashed by Hiroshima, in which all the common verities (faith and family, a sense of permanence) were forever undermined. Kerouac reflected this in the endless wandering of his characters, their restless movement, their belief that, in the words of Dean Moriarty, the antihero of his 1957 breakthrough novel, “On the Road,” “We know time.”

And yet, it’s a mistake to frame Kerouac as the point man for a movement, especially one as media-manufactured as the Beats. “Four people do not a generation make,” Corso once noted — a line that, its delightful irony aside, is exactly right. For Kerouac, the Beats were equally a convenience and a burden, a label that bought him notoriety even as it fenced him in. This tension extends to his work itself, which is radical in its evocation of a certain kind of consciousness and utterly traditional in its larger aims.

A dualism lies at the center of “The Sea Is My Brother,” with its back-and-forth between Wesley Martin, a merchant seaman, and Bill Everhart, a Columbia University lecturer who wants to see the world. Kerouac displays a certain insight into himself here. We see the essential conflict between the inner and the outer, the physical and the emotional, which would go on to define his writing, and would ultimately drive him mad. It’s the source of his spiritual questing, his extended involvement with Buddhism and his return to Catholicism, his drunkenness and his need for solitude. Read through such a filter, Martin and Everhart, far from being distinct characters, actually represent two sides of Kerouac.

Like much of Kerouac’s beginner writing, “The Sea Is My Brother” is claustrophobic, narrow in focus, disconnected from the complexities of life. It traffics not in archetype but in stereotype: the effete intellectual, the hard-drinking seaman, both of whom converse in speeches, offering not conversation but philosophy. Kerouac has not yet learned to let details do the heavy lifting, to find in the ecstatic rhythms of his language the narrative momentum that defines his later work. This is not a novel so much as a novel in suspension — all well and good, I suppose, except it brings us back to that unanswered question: How did Kerouac get from here to what came afterward?

Such a question is no longer Kerouac’s to answer, if indeed it ever was.