Elvin Morton Jellinek, known to his friends as Bunky, was born in New York in 1890, the son of a Hungarian actor and an American opera singer. When he was still young, the family moved to Budapest. By 1914, he had attended universities in his adopted hometown, as well as in Berlin, Leipzig, and Grenoble. Although he had studied philosophy, theology, anthropology, and linguistics, and learned to read twelve languages, he had never quite earned a degree. Back in Budapest, he got work as a currency trader, a post he kept until 1920, when he came under suspicion for having stolen a half million Hungarian crowns from his customers. He fled to the Serbian border, where guards refused him entry, but he managed to cross the Tisza by rowboat and disappeared.

No one knows exactly what Jellinek did for the next ten years, except that it involved changing his name to Nikita Hartmann, participating in an unspecified business in Sierra Leone, and then moving to Honduras, where he attended the University of Tegucigalpa and failed once again to get a degree. That didn’t stop him from calling himself a doctor. It also didn’t stop United Fruit from hiring him, under his original name, as a plant biologist, or the Worcester State Hospital from taking him on as a statistician, or the Research Council on Problems of Alcohol from giving him a job as an editor of its Quarterly Journal of Studies on Alcohol, or Yale University from appointing him to a post at its Laboratory of Applied Physiology, in 1941.

At Yale, Jellinek met Marty Mann, a socialite and a journalist whose struggles with alcohol had led her to the nascent self-help group Alcoholics Anonymous. She credited A.A.’s central tenet—that alcoholism is a disease—with rescuing her from drink and she devoted herself to promulgating the organization. Her dedication and Jellinek’s gift for promotion—of himself and otherwise—proved a powerful combination. By 1944, his lab had become the Yale Center for Studies of Alcohol, and the two had started the National Council for Education on Alcoholism, whose mission was to inform Americans of a “momentous” discovery: “that alcoholism is a sickness, not a moral delinquency.”

Jellinek found himself repeatedly defending that idea, especially to doctors, and in 1960 he decided to set it down in a book called “The Disease Concept of Alcoholism.” “The task is not as simple as it may seem,” he wrote. “One might say that all that is required is to state the criteria of alcoholism and to see whether or not they are in conformity with the definition of disease.” Alas, Jellinek continued, “Alcoholism has too many definitions, and disease has none.”

Much as a good definition of disease might have aided his cause, Jellinek did not mean to reproach medicine for operating without one. “The splendid progress of medicine shows that that branch of the sciences can function extremely well without such a definition,” he wrote. “Physicians know what belongs in their realm.” Still, however, for those who might insist, he offered his own: “A disease is what the medical profession recognizes as such.”

Like all tautologies, Jellinek’s is unsatisfying. But it is also correct: we have left it up to doctors to decide what kind of suffering qualifies for their ministrations. Usually, that’s not a problem. Patients and doctors alike, we can get along quite nicely without a better definition of disease. You’re coughing and running a fever, you have a broken leg, you’ve developed a burning rash: you and your doctor don’t philosophize about the ontology of your distress before you submit to treatment.

But then GlaxoSmithKline’s medical experts announce that your tendency to move about in bed is “restless-legs syndrome,” for which their Requip is the cure. Or the American Psychiatric Association declares that, as of May 22, 2013, Asperger’s syndrome will no longer be a disease but “binge eating disorder,” which occurs when you eat, “in a two-hour period, an amount of food that is definitely more than most people would eat in a similar period of time under similar circumstances,” will. And then you begin to wish that Bunky Jellinek had hung in there just a little longer before he punted, or at least that he’d recognized that, in a free-market economy anyway, it’s not such a good idea to let the people who profit from disease define it.

There is, of course, a working definition of disease, one that most of us share: a disease is a kind of suffering caused by something gone wrong in the body. Cancer, diabetes, tuberculosis—we label these diseases not simply because they inflict pain upon us, or impair the quality of our lives, but because doctors can specify their biochemistry—the neoplasms, the lack of insulin, the bacilli that can that can confirm the presence of the disease, that can be spotted and measured and, sometimes, eradicated.

A disease may be what the medical profession recognizes as such, but doctors are reluctant admit into their realm problems without some biochemical signature. Borderline cases—chronic fatigue syndrome, major depression, restless-legs syndrome—are vexing precisely because they lack those indicators. Doctors often leave conditions like these outside the pantheon of diseases, at least until they can demonstrate their biochemical cred. Which is why you shouldn’t be surprised to read sometime in the near future about a doctor who has inserted binge eaters into M.R.I. machines and proved that the disorder is a real disease.

The lack of this kind of proof that alcoholism is a disease is what led Jellinek to wrestle with the concept. It is also why the A.P.A. has to begin its Diagnostic and Statistical Manual of Mental Disorders with a loose and baggy four-paragraph definition of mental disorder that is no more satisfying than Jellinek’s was. Without biochemistry on their side, the authors of the manual have struggled to prove that the conditions they treat belong in the realm of physicians, and their efforts have done little to reduce suspicions that the profession is too eager to turn all our troubles into their disorders.

But psychiatrists are beginning to rethink this strategy. They are going on the offensive, claiming that psychiatry’s diagnostic uncertainty (and lack of biochemical findings) is pervasive in all of medicine. They point to the many physical illnesses—Alzheimer’s disease, peripheral neuropathy, even poison ivy rashes—diagnosed without resort to biological lab tests, and to the numerous diagnostic thresholds—such as glucose levels in diabetes and blood pressure in hypertension—that have been reworked over the years. So, they argue, it isn’t just psychiatry that fails to measure up to modern medicine. It’s also much of modern medicine.

Throwing their colleagues under the bus may or may not renew America’s confidence in psychiatrists. But it does have the virtue of being based on the truth. The idea that disease is a biochemical entity originated only in the mid-nineteenth century, when scientists like Louis Pasteur began to spot pathogens under microscopes and chemists like Paul Ehrlich began to fashion drugs that could kill them. In the first century after those discoveries, the new idea wrought miracles, turning illnesses like strep throat and diabetes, which once routinely killed us, into nuisances.