What weighs 21 grams?

Various sources suggest 21 paper clips, 21 cigarettes, five nickels, or one average mouse. It’s about 3/4 oz.

The reason anyone cares about that weight is that in 1907, Dr. Duncan MacDougall (1866-1920) put dying patients on a sensitive scale to try to capture the weight of their souls, by weighing the body before and after death. That was the figure he arrived at and, of course his experiments attracted much publicity, then and since.

In 2014, David Goudsward wrote about the affair in Wavelengths a publication based in Haverhill, Massachusetts, where Glasgow-born MacDougall lived and died:

In 1901, he decided to prove scientifically that the soul does exist. He transferred a terminally ill patient onto a cot placed on the scale and during the final hours of life, he measured the exact weight of the living person and adjusted for minute weight changes due to perspiration evaporating. When the patient died, he noted a sudden, unexplained weight drop. It was slight, but measurable. Encouraged by his results, he recruited several other physicians to assist his testing and over five years. More terminal patients were monitored. The administrators of the home were increasingly reluctant to allow the testing—if the results were erroneous, it would besmirch the home’s reputation, which it relied upon since it operated entirely through donations. If MacDougall was correct, he had transformed the eidolon of “the soul” into a hierophany and had opened a theological can of worms.

MacDougall continued to observe and measure patients for six years in the face of increasing friction from the home’s administrators. His sampling was as best sparce. He a total of six patients in all and of those six, he eliminated data on the sixth patient, who inconveniently died while the scale was being calibrated. Patient #4 was discounted as well, MacDougall felt the scale hadn’t been adjusted appropriately and the administrators had interfered with proceedings.

“Haverhill’s Man Who Weighed Souls,” June 28, 2014

So MacDougall didn’t really end up with that much information. But he did get a paper out of it in American Medicine in 1907, to say nothing of a story in the New York Times.

In recent years, a number of popular science publications have retold his story, and a Sean Penn film, 21 grams (2003), was inspired by it.

“Not a spiritual person”

At Popular Science, science writer Leah Hudson noted earlier this month:

Oddly enough, MacDougall was not a spiritual person. The Haverhill Evening Gazette described him as “hard-headed and practical,” with a scientific mind and a disinclination to believe in Spiritualism or psychic phenomena.

“He doesn’t sound like the kind of woo-woo, tarot-card reading, mystic type,” says bestselling science writer Mary Roach, author of Spook: Science Tackles the Afterlife.  At the time of his experiment, MacDougall was also described by The New York Times as a “reputable physician,” who had been working in the field for years.

“The 21 grams experiment that tried to weigh a human soul,” September 18, 2025

Perhaps he wasn’t. But he later turned his attention to attempting to photograph the soul, possibly in part because others were becoming queasy about the “weighing the dead” business, as Goudsward notes above.

Later researchers discredited MacDougall’s theory for a number of reasons:

Physicians picked the report apart and MacDougall was overwhelmed trying to defend his work. With no further revelations forthcoming, the mainstream press lost interest and the medical profession ignored the entire unpleasant affair. Weighed Souls”

Why did McDougall think souls had weight?

He appears to have thought that he could establish the existence of the soul by proving that it had weight, possibly because he believed that it must be material in order to exist. That’s an eccentric concept.

Traditionally, the human soul has been understood as quite real but immaterial and non-local. It is instantiated in a body, which is material and local. In that respect, some of the characteristics of the soul are like those of an idea.

Ideas are immaterial but, if they make any difference, they become instantiated in material things. The idea of patriotism, for example, is often instantiated in a flag. Thus, a great deal of etiquette and emotion develops around the flag. Anyone who thinks that patriotism is not real because it is “just a concept” has not paid attention to patriots reacting to an instance of flag-burning, let alone war…

Even some things that we think are very material, like our bank accounts, turn out, on examination, to mostly be a series of ideas and assumptions shared by many people.

Today, the study of the soul focuses more on near-death experiences, especially those where the information that the experiencer provides can be confirmed. Efforts to try to somehow “catch” the soul belong more to the world of folklore.

You may also wish to read: An ancient argument for the existence of the human soul. Sixteen hundred years ago, Augustine told a friend about a dream a skeptical local doctor had had. In the dream, a sharp youth asked the doctor some pointed questions he couldn’t answer. One issue that arose in that age of philosophical controversy, just as today, was how anything like a human mind could function without a body?