American religion is in a state of flux.

Religious “nones,” a category that includes atheists, agnostics and those with no affiliation to organized religion, now make up roughly a quarter of the American public. It’s a rapidly growing group ― now constituting the second largest “religious” category after evangelical Christians. And the designation is highly common among millennials, a trend likely to persist with every subsequent generation.

Nearly 80 percent of “nones” were raised in a religion they chose to leave behind once they reached adulthood. A recent survey conducted as part of Pew Research Center Religious Landscape Study investigates why these former faithful left the fold ― and the reasons they gave are illuminating.

Forty-nine percent of religious “nones” who were raised in a religion say they simply stopped believing. That was true for 82 percent of atheists and 63 percent of agnostics. Many respondents mentioned science, saying their views evolved over time. Others said they became disenchanted with the faith.

American belief in God has wavered on the whole. Fifty years ago, a whopping 98 percent of Americans said they believed in God. That number has fallen roughly 10 percentage point over the years, and among millennials, the share of believers is down to 80 percent.

One in five “nones” surveyed by Pew said they left their faith due to a dislike for organized religion. Some mentioned the Catholic Church clergy sex abuse cases, while others said they felt organized religions were just out to make money off their followers. And in these times of religious strife and discrimination, many “nones” felt that too much harm has been done in the name of religion.

An earlier Pew survey looked at where “nones” find a sense of morality, given that many social values have historically been thought to derive from Judeo-Christian teachings. Unsurprisingly, the answers that topped list for “nones” were things like honesty, gratitude and spending time with family.

Fifty years ago, a whopping 98 percent of Americans said they believed in God. Now, roughly half of those who have left religion behind say they simply stopped believing.

Almost 30 percent of “nones” surveyed in the latest Pew report say they’re either religiously undecided or inactive believers ― suggesting they haven’t abandoned religion altogether. Some say they’re too busy to practice, while others say they’re keeping an open mind and haven’t settled on a particular tradition.

In 2014, Pew found that nearly half of the religiously unaffiliated felt a sense of wonder about the universe. That included 54 percent of atheists and 55 percent of agnostics.

What we’ve been calling religion, or even spirituality, might simply not encompass what more and more Americans are experiencing in their daily lives. Things like “wonder” and “awe” might be more apt descriptions than “faith” or “piety” to explain the lived experience of that-special-feeling-that-can’t-quite-be-defined.

And Americans aren’t foregoing the community aspect of faith, either. More and more religious “nones” are forging new communities ― from meditation groups to Sunday Assemblies ― in which to gather and make sense of this wonderful thing called life.