Given that Maggie Nelson is known for expanding categories and defying the expectations of genre, it's little wonder, perhaps, that her latest book, the subtle yet wide-ranging "On Freedom: Four Songs of Care and Constraint," would take as its subject the quality or state of being free (if one defines it positively), or the power or condition of acting without coercion (if one defines it in relation to what it's not).

Although therein lies much of this book's allure, because what do we even mean when we say freedom? "Part of the trouble resides in the word itself, whose meaning is not at all self-evident or shared. In fact, it operates more like 'God,' in that, when we use it, we can never really be sure what, exactly, we're talking about, or whether we're talking about the same thing," Nelson writes in her introduction.

The author of nine previous books — including, most recently, 2015's National Book Critic's Circle Award-winning "The Argonauts" — Nelson is a broad thinker, concerned with ethics, and careful to balance emotion with intellect. Far less memoiristic than "The Argonauts," "On Freedom" is more focused on cultural criticism and philosophizing, exploring its capacious topic through the frames of art, sex, substance use and climate change.

Nelson's applications of these restrictions to her seemingly limitless topic feels savvy because — rather than offering a polemic or manifesto on personal or political freedom — she addresses "the ways in which freedom appears knotted up with so-called unfreedom, producing marbled experiences of compulsion, discipline, possibility, and surrender."

In each of the book's four sections — "Art Song," "The Ballad of Sexual Optimism," "Drug Fugue" and "Riding the Blinds" — Nelson grounds this subject, which tends toward heady abstraction, in concrete specifics. All the while, she expresses her skepticism "about turning more and more arenas of life (teaching, activism, art) into caretaking and therapy."

Characteristically, Nelson's text is thick with references to other writers and thinkers, putting her own observations in juxtaposition with those by Foucault, Arendt, Baldwin, Rancière and many, many more. Moreover, "On Freedom" has a full 55 pages of notes at the end, like a hallway of doors, all waiting to be opened and entered should the reader desire to journey even deeper into the subject with Angela Davis, Lauren Berlant, Fred Moten and Nietzsche as guides, to name but a few.

Nelson currently teaches at the University of Southern California and draws on her previous experience teaching at CalArts, and reading this book feels like being in the presence of an inspiring professor, someone who has a great deal to show you, but ultimately wants to show you most of all how to think for yourself.

"If ceding freedom to noxious forces is a grievous error, so, too, is holding on to rote, unventilated concepts of it with a white-knuckled grip," she explains of her motivations. By the end of her theorizing, Nelson has breathed fresh air into the title notion, and in her openhanded treatment has given her readers a chance to consider freedom more freely.

Kathleen Rooney is the author of "Lillian Boxfish Takes a Walk" and, most recently, "Cher Ami and Major Whittlesey."

On Freedom

By: Maggie Nelson.

Publisher: Graywolf Press, 288 pages, $27.