A substantial and growing share of American adults describe themselves as spiritual but not religious. The phrase marks a separation between two things that were long assumed to travel together.
Affiliation and belief are different measures
Surveys track several distinct things: membership in a congregation, attendance, stated belief, and private practice such as prayer or meditation.
Affiliation and attendance have declined more sharply than belief, which is the gap the phrase names.
Treating those measures as one produces confusion, since a decline in one is regularly reported as a decline in all of them.
Institutions carry costs that private practice does not
Belonging to a congregation involves time, money, agreement with positions taken publicly, and association with an institution's conduct.
Private practice carries none of those, which means the two respond to entirely different pressures.
People who left institutions frequently describe the reasons in institutional terms — how a body handled a controversy, or a position on a social question — rather than in terms of belief.
Authority is located differently
The phrase generally implies that the individual is the arbiter of what is meaningful, rather than a tradition, text or clergy.
That is a genuine shift in where authority sits, and it aligns with broader American patterns of declining confidence in large institutions of every kind.
It also makes the category internally varied, since people locating authority in themselves arrive at very different conclusions.
What congregations provided beyond belief
Religious institutions historically supplied a great deal that was not doctrinal: a weekly gathering, intergenerational contact, practical help in crisis, and structure around births, marriages and deaths.
Those functions do not disappear when affiliation does, and researchers studying social connection have noted the difficulty of replacing them.
Some people assemble substitutes from other sources; others describe the loss without having found a replacement, and both patterns appear in the data.
The category is contested from both sides
Religious critics argue the phrase describes preference without obligation, and that traditions are demanding by design in ways private practice is not.
Those who use it argue that institutional membership was never a reliable indicator of inner life, and that the separation makes an old distinction visible.
Both positions describe something real, and the disagreement is about what counts as religion rather than about what the surveys measured.