Carl Jung is back. Well, in a minor way. In the sense of, like, never having entirely disappeared since his death in 1961. Jung is the little train engine of psychology: still in service, still hauling freight and passengers on a narrow-gauge railroad off somewhere in the distance. Never the main line, but maybe for that reason never an abandoned line, either. And every 10 years or so, something causes readers to notice that Jung somehow endures, chugging along as he always has.

That is not nothing. There was a time, as late as the 1960s, when Sigmund Freud, Alfred Adler, and Carl Jung were powerful names to throw around in literary criticism, social analysis, and cultural examination. That triumvirate of founders of psychoanalysis disagreed wildly and bitterly among themselves, but no one doubted that they had found something profound about the human psyche. The psychoanalytic method, we were taught to think, was a key that had unlocked the doors of self-understanding.

These days, Freud is mentioned mostly as cautionary tale. He may have seemed a revolutionary figure, once upon a time; dozens of books were written about the masters of suspicion—Darwin, Marx, and Freud—who smashed the stuffy religious hypocrisy of the 19th century. But now Freud is gestured at by the cognoscenti only in the mode of negation: a reactionary figure whose outdated ideas about such things as penis envy, the Oedipus Complex, and polymorphous perversity held back the sexual revolution that set us all free to express guiltlessly whatever sexual desires we seem to feel.

At least Freud still gets mentioned. In truth, Alfred Adler may be the figure with the largest direct impact on the contemporary practice of clinical psychology—beginning with our modern rejection of "psychoanalysis" in favor a more populist "counseling" (for which one can be licensed with much less education). But his outsized influence since his death in 1937 seems to have done little to preserve his name. Even psychological counselors rarely refer back to Adler. The most visible psychological advances over the past 30 years have come with drugs, and the apparent successes of psychopharmacology have reflected badly on Adler's versions of the talking cure for the most profoundly insane.

And then there's Jung. Imprint catalogues have promised publication this fall of Ruth Williams's C.G. Jung: The Basics, Lynn Brunet's Answer to Jung, the Jung Foundation's The Art of C.G. Jung, Peter Kingsley's Catafalque: Carl Jung and the End of Humanity, Susan Rowland's Jungian Literary Criticism: The Essential Guide, Andrew Kuzmicki and Ilona Blocian's Contemporary Influences of C.G. Jung's Thought, and more besides. This summer saw half a dozen more books, from Harry A. Wilmer's Practical Jung to James Johnston's Jung's Indispensable Compass.

Jung has always attracted those who take the road less traveled. Readers interested in reconciling Swedenborgianism with the thought of Jung, for example. will find several books in print to help them. Every third or fourth volume from a New Age publisher will deploy Carl Jung's name in hopes of lending weight to its ethereal text.

Meanwhile, any number of self-help books use Jung's 1921 listing of "personality types" to sort readers into appropriate categories. Recent months have seen such Jung-influenced publications as, for example, John van der Steur's First, Know Your Self: A Guide to Discovering the Power of Your Personality. Or, for that matter, 12 Rules for Life: An Antidote to Chaos, the bestseller from the self-proclaimed Jungian psychologist, Jordan Peterson.

In other words, Jung seems to possess a curious exemption, small but real, from contemporary suspicion about old psychology. A good example can be found in the reviews this month of Merve Emre's new book, The Personality Brokers: The Strange History of Myers-Briggs and the Birth of Personality Testing. In one sense, there's nothing path-breaking in Emre's text. No scholar of psychology in a generation has taken the Myers-Briggs Personality Test seriously.

In another sense, however, Emre has written an important work, for many businesses still use the Myers-Briggs test to sort potential employees, and many schools still use it to direct students toward the careers that are thought to fit what the test determines are the students' natural personality types. And as an account of the nutty origin, peculiar growth, and deleterious effect of the test published in 1944 by Katharine Cook Briggs and her daughter Isabel Briggs Myers, Emre's The Personality Brokers can't be bettered.

And yet, an interesting feature of the reviews—and of the book itself—is the refusal to attach much blame to Carl Jung. By every account (including her own, in "Up From Barbarism," the science-conquers-all article she wrote for the New Republic in 1928), Briggs used Jung's 1921 work extensively while constructing her personality types. But nearly every review has followed the book in noting that "Jung was insistent that his personality types only reflected preferences, not inherent abilities." Briggs and Myers were autodidacts who suffered from all the usual deficiencies of the self-taught: overconfidence and overselling, notably, with an inability to admit the existence of doubt or even nuance. Sure, personality tests all use Jung, we are told, but in important ways, they misuse Jung. The thought of the man himself is better than that.

And so, in fact, it is. Jung was a polymath of extraordinary breadth. But more important is the depth of his intellect. From the psychology of the unconscious to the Book of Job, he showed a power to concentrate and bring enormous amounts of thought to a topic. His notions of, say, the collective unconscious and universal archetypes are what draw to him some of the gooier contemporary writers, just as his interest in personality attracted the dubious allies of Katharine Cook Briggs and Isabel Briggs Myers. But the ideas themselves, in the nuance of Jung's original accounts, are not ruined as a result.

And those ideas of the collective unconscious and universal archetypes offer certain advantages in intellectual discourse—advantages that Jordan Peterson seizes in the public lectures and debates that have made the Canadian psychologist a YouTube star. Think of it this way: Some good-sized segment of contemporary audiences hungers for discussion of the deep stuff of human existence. Birth and death. Good and evil in their behavioral forms of benevolence and malice. For that matter, good and evil in their cosmic forms of God and Satan. The light that we struggle to follow and the darkness that closes in on us.

To discuss these things typically requires a move to metaphysics, and metaphysics is lumped these days with religion: a field in which one can claim only belief, not knowledge. Jungianism, like much modern thought, cedes all that metaphysical territory. Nothing we say, nothing we discuss or analyze, tells us anything about the metaphysical truth of the soul or God, Heaven or Hell. But—and here's the key clever move—we needn't concern ourselves about the extra-mental reality of such things, because they exist as ideas, archetypes, in the collective unconscious. People know these things through their shared symbols, regardless of their truth, and that's enough to be going on with.

Going on with for quite a ways, in fact. Down the narrow-gauge railroad of the side lines traversed by that curious engine of Carl Jung.