While working on the 1985 book "Habits of the Heart," the late sociologist Robert N. Bellah met "Sheila," who described her faith in words that researchers have quoted ever since.

"I can't remember the last time I went to church," she said. "My faith has carried me a long way. It's Sheilaism. Just my own little voice." The goal was to "love yourself and be gentle with yourself. … I think God would want us to take care of each other."

A decade later, during the so-called "New Age" era, researchers described a similar faith approach with this mantra -- "spiritual but not religious."

Then in the 21st Century's first decade, the Pew Research Center began charting a surge of religiously unaffiliated Americans, describing this cohort in a 2012 report with this newsy label -- "nones."

Do the math. "Nones" were 10% of America's population in 1996, 15% in 2006, 20% in 2014 and 26% in 2019. This stunning trend linked many stories that I have covered for decades, since this past week marked my 33rd anniversary writing this national "On Religion" column.

Obviously, these evolving labels described a growing phenomenon in public and private life, said political scientist Ryan Burge of Eastern Illinois University, author of the new book, "The Nones: Where They Came From, Who They Are, and Where They Are Going."

But hidden under that "nones" umbrella are divisions that deserve attention. For example, the 2018 Cooperative Congressional Election Study found that 5.7% of the American population is atheist, 5.7% agnostic and 19.9% "nothing in particular."

"When you say 'nones' and all you think about is atheists and agnostics, then you're not seeing the big picture," said Burge, who is a contributor at the GetReligion.org website I have led since 2004. "Atheists have a community. Atheists have a belief system. They are highly active when it comes to politics and public institutions.

"But these 'nothing in particular' Americans don't have any of that. They're struggling. They're disconnected from American life in so many ways."

In his book, Burge stressed that "nothing in particulars are one of the most educationally and economically disadvantaged groups in the United States today."