Mr. Mustin, an English teacher from South Carolina, asked why we describe something as a “watershed moment,” and I realized I didn’t know.
Great question! Here’s what I found:
“Watershed” originated as a term that describes the landscape, but it has different meanings in American and British English.
'Watershed': American English
In the US, a “watershed” is an area of land that eventually drains into a body of water. For example, if rain falls on some land and that water ends up in the Boise River, then that land is part of the Boise River Watershed.
'Watershed': British English
In Britain, it’s a little different. The watershed is the ridge or crest that divides water that flows into different basins (or what we’d call watersheds in the US). So by the British definition, water flows into different drainage basins on different sides of a watershed. And it’s this British meaning that gives us the more metaphorical meanings of “watershed” that Mr. Mustin was asking about because a “watershed” or “watershed moment” is something like a dividing line between two events or times.
For example, a famous quotation often attributed to William Faulkner or Frank Lloyd Wright is “A man is a fool if he drinks before he reaches the age of 50, and a fool if he doesn’t afterward.”
The Quote Investigator website, which looks at the origin of quotations, found that this quotation was popular among doctors long before Faulkner or Wright could have said it, and the site describes the turning point in the quotation as the “watershed age.” It says, “The watershed age was variable; sometimes fifty was specified and sometimes forty.” At the time, doctors believed that before that age you shouldn’t drink, whether it was 40 or 50, and after that age you should.
As Mr. Mustin noted, when “watershed” is used metaphorically, it’s often followed by the word “moment,” as in this quotation from Walter Cronkite about the death of Winston Churchill:
"The death of Churchill at 90 was one of those watershed moments in which the obituary rises to a special calling beyond the sharing of remembered times. It gave an older generation a rare opportunity to explain something of itself to its children.”
In that case, “watershed moment” is used to mean something like “an important moment,” but it still has a sense of a division or a dividing line—that there’s a difference in knowledge between the older generation and the younger generation.
The British Television Watershed
Interestingly, in British English, “watershed” also has developed a specific meaning related to television. It’s still a division, but it’s the specific division between the time when stations can air shows that are appropriate for all audiences and the time when they can air shows that are just appropriate for adults. For example, a 2015 headline in The Guardian, a British newspaper, asks “Should the 9pm television watershed be abolished?”
I hope this will help you understand and use the term “watershed moment” a little better. It can be a little confusing since the topographical meaning is different in British English and American English, but they both involve water running in different directions. A watershed moment isn’t just an important moment. It’s a moment that has a specific before and after. Before the watershed moment, things were one way, and after the watershed moment, they are different.
Image courtesy of Shutterstock.
Mignon Fogarty is Grammar Girl and the founder of Quick and Dirty Tips. Check out her New York Times bestseller, "Grammar Girl’s Quick and Dirty Tips for Better Writing."