Conceived well before the coronavirus hijacked our lives, “Sick Souls, Healthy Minds” offers us a lifeline at this moment. Many of us, forced into a state of suspended animation, now have time to think. As we tell each other what to watch, what to cook, what to read and what exercises to do, John Kaag invites us to ask, together with America’s greatest philosopher, William James, what makes life worth living.

When we can leave our cocoons, browsers are likely to find Kaag’s book in the self-help section of their local bookstore. Yet readers lured by its subtitle, “How William James Can Save Your Life,” will soon find themselves wrestling with philosophy, psychology and religious studies, though not in scholars’ bone-dry prose. Instead Kaag, a philosophy professor at the University of Massachusetts at Lowell and a twice-divorced, self-described social misfit, lets readers into his own attempts to stave off depression when he felt the walls of his life closing in.

The book opens with the grisly scene that greeted Kaag one winter morning in 2014. Harvard student Steven Rose had committed suicide by jumping from the roof of the university’s 15-story William James Hall just before Kaag passed by on his way to Widener Library. Rose’s death forced Kaag to ask himself hard questions: Why do some people choose to end their lives? How can we avoid that fate ourselves? “Sick Souls, Healthy Minds” offers his answers.

Throughout the book, Kaag connects painful experiences from his own life to James’s physical, psychological and emotional ordeals, and shows how James came to understand and overcome what ailed him. And James had his troubles: a brush with suicide in his 20s, persistent health problems, the back-to-back deaths of his father and an infant son, and nagging doubts about the value of his professional work. Yet he repeatedly climbed out of the despair that afflicts “sick souls” by unsnarling the philosophical issues beneath the problems he faced.

In the late 19th century, influential philosophers and scientists argued that all human behavior is determined. Drawing on positivist philosophy and Darwinian biology, such thinkers insisted, as some 21st-century neurophysiologists and evolutionary psychologists do, that free will is nothing but an illusion. If so, what’s the point of living? James dealt with his own existential anxiety by pointing to the most basic experience of choice we all know, the decision to focus our attention on one thing — say, this review — rather than another. He also decided to act accordingly: He declared that affirming free will was his first deliberate act of freedom. James lost his father and his son Herman in 1885, while he was working on his landmark “Principles of Psychology.” Coping with the interiority of his personal pain helped him see immediate experience in a novel way. Neither philosophy nor psychology can penetrate or explain the ineffable stuff of human consciousness, James argued — and Kaag agrees — because individuals’ inner lives will always elude students of physiology or behavior.

James pioneered the idea that consciousness is a continuous stream in which past, present and future blur together in the kaleidoscope of immediate experience. He also explored the paradox of habits, indispensable to healthy living yet sometimes a threat to the unexpected moments that make experience vivid and meaningful. Life is “an alternation of flights and perchings,” James wrote. It is in the transitions, where life can “grow by its edges,” not in the comfortable routines that enmesh us, that we find what Kaag calls the meaning and value of “enduring goods [both] moral and aesthetic.” James argued that value judgments result from individual choices; they are rooted in personal and collective experience rather than unchanging principles of reason.

James’s critics for a century have misunderstood his philosophical pragmatism as authorization for whatever is expedient or as simple relativism. Instead it reflected James’s understanding that in domains such as ethics, social and political life, and religious faith, we can never attain certainty. We are doomed — and we are free — to play our part in an extended process of trial and error, endlessly verifying and falsifying claims about truth. When there are no fixed answers, we can test our hypotheses only by acting on them with our lives and assessing the “practical consequences.” Those consequences must be judged not for oneself alone, or for the moment, but more generally and over the long haul. For just that reason James, never a churchgoer himself, refused to rule out the possibility of religious belief. He respected people who searched for something beyond the everyday, whether in nature or drugs or mystical experiences, that spoke to them about the deeper meanings of life.

I have been teaching James’s ideas for 40 years in courses on American intellectual history. Students almost always report that the most important text for them is James’s “On a Certain Blindness in Human Beings,” which Kaag prizes for the same reasons my students do. The essay alerts us to the special significance that all people attach to their inner lives, precious beyond measure and inaccessible to anyone else. The “zest” we feel for our passions often blinds us to the special significance other people attach to their own immediate experience. James proposed a novel way to think about community, not as a collection of like-minded people but instead as a constellation of unique individuals, each enjoying one-of-a-kind inner awareness that we should not just tolerate but treasure.

James would have liked this book. Kaag ties James’s ideas directly to the challenges and puzzles of his own life — and his readers’ lives. How should we deal with isolation or rejection? How do we fall in — and out of — love? How should we raise our children? How do we escape the numbing throb of our daily routines to savor life’s possibilities? James’s students, including such notables as Theodore Roosevelt (whose bluster he loathed), Gertrude Stein, W.E.B. Du Bois, Walter Lippmann, T.S. Eliot and Alain Locke (all of whom he loved), revered him because he addressed the meaning of life. Although many academics avoid that topic in their classrooms, everyone should take time to think about it, especially now. James’s ideas have rippled through the past century more powerfully than those of any other American thinker. Kaag’s little book reminds us why.

Sick Souls, Healthy Minds

How William James Can Save Your Life

By John Kaag

210 pp. $22.95