Surveys of American religion consistently find a large group describing themselves as spiritual but not religious. The category is real, and it is less coherent than its size suggests.
Survey wording created the category
Researchers began asking separately about religiousness and spirituality, which allowed a response combination that earlier instruments could not record.
Once available, the option was chosen widely, and the resulting group is defined by what respondents decline rather than by anything they share affirmatively.
Groups defined by rejection tend to be internally diverse, which is why the label predicts belief and practice much less well than researchers initially expected.
Religious identification and practice diverged
Affiliation with a congregation has declined in the United States over recent decades, and attendance has declined further and faster than affiliation.
Belief in something beyond the material world declined much less, leaving many people holding beliefs without an institution attached to them.
The label captures that gap, describing a location relative to institutions rather than a distinct set of convictions, which is why it grew fastest during the period when attendance fell.
Younger cohorts drove much of the change, and cohort replacement rather than individual conversion accounts for a large share of the aggregate movement.
Religious means institution to most respondents
When asked to explain the distinction, respondents typically associate religious with organizations, doctrine, hierarchy and obligation.
Spiritual is associated with personal experience, individual searching and a sense of connection that does not require anyone else's authorization.
The distinction is therefore largely about authority and autonomy, which is why it maps onto broader American attitudes toward institutions generally.
Practice becomes assembled rather than inherited
Without a congregation supplying a calendar, a community and a set of practices, individuals assemble their own from available sources.
Assembled practice tends to be less regular, since nothing external schedules it, and less communal, since the community was the part the institution provided.
This is the recurring finding in studies of the group, and it is the aspect participants themselves most often name as a loss.
Why the label resists measurement
Two people selecting the same response may mean entirely different things, one holding traditional beliefs while disliking congregations and another holding none.
Aggregating them produces a number that is accurate about the response and uninformative about belief, which is a general hazard of survey categories.
Reporting on religious change is more reliable when it addresses specific practices and beliefs rather than identity labels people apply to themselves.