Little Edie Beale in Grey Gardens, the home she shared with her mother, in 1972. Photograph by Tom Wargacki / WireImage

My mother survived to the age of ninety-three, so she had time to develop a number of habits that people now consider to be symptomatic of dementia. Hoarding, for example. She lived in Santa Barbara, in an apartment with a perfectly adequate kitchen, but in order to store her dishes she had to buy a freestanding cabinet and install it in the dining room. She needed her kitchen cupboards for other purposes, such as her collection of polystyrene food containers. In her late years, my mother underwent several operations, and, for a long time, after she came home, Meals on Wheels delivered her dinner. Secretly, she wanted no part of the food. What she did like, however, was the receptacles the dinners came in. These boxes, with the flip-up lids, are common trash items of our time. But to my mother they were exotic, and attractive: gleaming and white, with little compartments, like a jewelry box. She told me that she might use one as a desk organizer, or perhaps a sewing kit, with different kinds of buttons in the wells. I don’t know what she did with the dinners, but the containers were washed, patted dry, and carefully stacked on their designated shelves.

Then, every year, shortly before Thanksgiving, I would fly in from New York to visit her, and the first thing we did on the morning after my arrival was clean out the polystyrene-container cupboard. I would get up on a stepladder, with a trash bag, and dump the containers in, one by one. She would stand below me, in her blue robe, her eyes sparkling with—what? Grief? Anger? Eagerness to fill the newly vacated space? I told myself that I was doing her a favor, and I was. I was helping to keep her apartment in the kind of shape where no one could come in and say that she had to be moved to a nursing home—a possibility that she actively feared. Still, the clear-outs were hard for her. Soon, she knew, she was going to lose everything she had, because she was going to lose her life. Until that happened, she was making sure that she had plenty of things. And here I came, year after year, throwing them away.

She died in 2010, and so she never had to find out that in 2013 the American Psychiatric Association declared her storage habits a diagnostic feature of a mental illness called “hoarding disorder,” or H.D. As defined by the A.P.A., H.D. is a persistent difficulty in discarding possessions, regardless of their actual value, to the point where the person’s accumulated goods congest living areas and impede their intended use. Hoarders also tend to go in for energetic collecting, often at inexpensive emporia—thrift shops, yard sales, and the like. The items most commonly hoarded, the A.P.A. says, are newspapers, magazines, old clothes, bags, books, mail, and paperwork, though valuable materials—indeed, cash and checks—may also be included with the junk.

The document in which these guidelines are laid out is the fifth edition of the A.P.A.’s Diagnostic and Statistical Manual of Mental Disorders (2013), or DSM-V. The first edition was published in 1952; since then, it has undergone five substantial revisions, and, in the process, the concept of psychopathology has broadened. For a number of years now, you haven’t had to do anything especially eye-catching to make it into the manual. DSM-V has a new category, “excoriation (skin-picking) disorder,” which is where you could end up if you don’t stop picking your cuticles. In a section called “Conditions for Further Study,” the manual lists behaviors that it isn’t calling disorders yet but is asking us to think about. Consider one: “persistent complex bereavement disorder.” That’s when you can’t get over the death of someone close to you within the period of time that the DSM considers to be appropriate: a year if you’re an adult, six months if you’re a child. If you fail, the manual suggests, you may be the victim not only of grief but also of illness, which calls for treatment.

Just as bereavement has an ordinary cause (death), so hoarding may be the product of unremarkable circumstances—notably modern medicine, which allows us to live longer. DSM-V says that hoarding sometimes begins in childhood, but that by the time the hoarders come to the attention of the authorities they tend to be old. This makes sense. The aged have fewer pleasures than younger people do, and therefore may be more tempted by the prospect of having plastic flyswatters in five different colors. Also, old people are likely to be living alone, without someone to tell them that they are doing something unusual, or to make them care about that fact. Finally, there is the economic factor. If our grandmothers and our great-grandmothers keep bags of string, that may be because they may remember a time when they had no string.

Normal as all this sounds, there are cases of hoarding that don’t fall within the boundaries of the normal, and these are the subject of “The Hoarders: Material Deviance in Modern American Culture” (University of Chicago), by Scott Herring, a professor of English at Indiana University. Probably the most famous American case—Herring leads with it—is that of Homer and Langley Collyer, two brothers who lived in an imposing four-story brownstone at Fifth Avenue and 128th Street, in Manhattan, in the first half of the twentieth century. The Collyers were the sons of a distinguished family. Their great-grandfather built one of the largest shipyards on the East River. Their father was a respected obstetrician. Both boys went to Columbia University, Homer receiving a degree in law, Langley in engineering. But the family had a long vein of eccentricity. The father, on days when his work called him to City Hospital, on Roosevelt Island, is said to have paddled there in his canoe and, at night, paddled back to Manhattan and carried the canoe home.

The brothers worked for a while, but gradually they stopped, and allowed their phone, gas, electricity, and water services to lapse. In time, they began ignoring their tax and mortgage bills as well. Homer eventually went blind, and developed a near-paralytic rheumatism. After that, he did not leave the house. Langley took care of him. He, too, then rarely went out except late at night, usually to find food. But what most surprised the neighbors was the amount of debris that the Collyers seemed to be accumulating. Rumors circulated that the men were rich, and had stashed a lot of money in the house. Hence there were numerous break-ins. The would-be burglars apparently found no cash but, instead, fabulous mounds of junk.

In 1947, a caller alerted the police that someone in the Collyer mansion may have died. After a day’s search, the police found the body of Homer, sitting bent over, with his head on his knees. But where was Langley? It took workers eighteen days to find him. The house contained what, in the end, was said to have been more than a hundred and seventy tons of debris. There were toys, bicycles, guns, chandeliers, tapestries, thousands of books, fourteen grand pianos, an organ, the chassis of a Model T Ford, and Dr. Collyer’s canoe. There were also passbooks for bank accounts containing more than thirty thousand dollars, in today’s money.