For a writer who has written about, and often lived with, characters as far flung as San Francisco drug addicts, the Mujahedeen, Russian composers, skinheads, Thai prostitutes, Copernicus, and has produced a series of dreamlike novels tracing the first Native American encounters with Europeans, William Vollmann has managed the nearly impossible task of creating a body of work that wrings some sort of order from the chaos of such disparate phenomena.

In both his fiction and nonfiction — and those places where the two meet — the broken and dispossessed reign supreme. Now, just three years after his 3,300-page, seven-volume treatise on violence, “Rising Up, Rising Down,” and two years after his brooding National Book Award-winning novel “Europe Central,” Mr. Vollmann has returned with a much smaller, more tightly organized work, a meditation on poverty, simply titled “Poor People” (Ecco, 314 pages, $29.95).

“Poor People” doesn’t mark a departure from Mr. Vollmann’s usual fare. In fact, it recalls nothing so much as Mr. Vollmann’s 1996 book “The Atlas,” a collection of short fiction and reportage that ranged from the not unrelated perils and thrills of war to prostitution drug addiction, jumping from place to place and year to year, while maintaining a steady tone and a certain morality. Mr. Vollmann allows himself to become personally involved with his subjects yet remains an outsider, stepping outside the reality of his subjects’ existence in order to place their stories in some kind of sociohistorical context.

Mr. Vollmann has arranged “Poor People” under a series of “self-definitions.” His subjects try in their own way to answer his question: “Why are you poor?” Like Alexis de Tocqueville’s 1835 essay “On Pauperism,” which set out to explain why some live in poverty while others flourish, Mr. Vollmann travels to countries famous for their poverty, and those, like America and Japan, where the poor may be numerous, but largely invisible.

Mr. Vollmann cautions throughout that he is not trying to develop a theory of poverty or offer scientific reasons as to why some succeed while others fail. “For me,” he writes, “poverty is not mere deprivation; since people may possess fewer things than I and be richer; poverty is wretchedness. It must then be an experience more than an economic state. It therefore remains somewhat immeasurable.”

Immeasurable though the condition may be, Mr. Vollmann elucidates some core truths about the discrepancy in means between himself and his subjects, but his conclusions are presented subjectively. “It goes without saying that I consider the woman who spends her days behind a water buffalo to be as worthy as I,” he writes. “I can easily suppose her to be as happy as I, or happier. Why then do I fear to become her? It can only be because I judge her situation inferior to mine.” This is not the woman’s fault, or because she as a person is inferior to him, he reasons, but because “most pleasures I prize — reading, writing, appreciating reality’s variety in my own way — all these require money.” Here he echoes Tocqueville, who held that “at the outset men had scarcely anything but natural needs, seeking only to live; but in proportion as life’s pleasures have become more numerous, they have become habits.” It is our ability to afford these habits that makes poverty, and the sometimes fuzzy distinction between wants and needs, such a fluid thing, and so terrifying to those with means.

Yet, recalling the mania for categorization that was so pervasive in “Rising Up, Rising Down,” Mr. Vollmann does offer a set of “Phenomena” which he claims the poor in any country are victims of: Invisibility, Deformity, Unwantedness, Dependence, Accident-Prone-Ness, Pain, Numbness and Estrangement. All of these conditions either give rise to poverty, or are the conditions under which the poor labor, according to his calculus. In one way or another, the poor are like others for whom we have little wish to see or dwell on: the dead. “The dead are gone, invisible to us. But that’s because we bury them in the ground where we won’t have to smell them. Why is an opened grave a fearful thing? For the same reason that visible poverty is.”

Mr. Vollmann’s talent is the ability to sympathize with unsympathetic characters, which allows him to judge them even while displaying enormous patience. It’s a near impossible trick, and he succeeds only partially, giving his analysis — literary and purposefully unscientific as it is — a sentimental quality. Not sentimental in the sense of painting the poor heroic, or wallowing in their miseries and humiliations, but more of a sad-eyed empathy married to a freewheeling literary license, all wrapped around his rejection of journalistic objectivity in sketching his character studies. Through it all, Mr. Vollmann recognizes the character flaws that led his subjects into poverty in the first place, and while he writes sympathetically of them, refuses to temper his judgment. In this way, his criticism of James Agee’s and Walker Evans’s “Let Us Now Praise Famous Men” as “an elitist expression of egalitarian longings,” fits with his overall approach, since Mr. Vollmann never makes poverty look like a character-building exercise.

This method is on full display in the case of Sunee, a mother of an adolescent girl and “a drunk, divinely predestined to poverty” with whom Mr. Vollmann spent time in Thailand. After she repeatedly spends the money Mr. Vollmann gives her to care for her daughter on alcohol, he exclaims, “Why are some people so doomed?” For this he has no answer, and to his credit, knows that it’s impossible to offer one in the pages of a book, even one as tenderly and thoughtfully written as this one.

Mr. McLeary is a staff writer for the Columbia Journalism Review.