This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Academic interest in prayer as a subject in its own right, rather than as raw material for theology, is usually traced to the psychologist William James, whose 1902 lectures published as The Varieties of Religious Experience treated firsthand accounts of prayer and religious feeling as evidence to be examined rather than doctrine to be either defended or dismissed. The German scholar Friedrich Heiler followed with the first systematic comparison across traditions, proposing a typology running from petitionary prayer asking for a concrete outcome through to a mystical prayer seeking union with the divine and dissolving the sense of a self doing the asking.
That comparative project continues today mainly through anthropology and the psychology of religion, both of which study what praying does for the person praying and for their community, how a prayer is learned, transmitted and altered across generations, and how differently traditions understand what, if anything, a prayer changes. None of that research requires taking a position on whether a prayer is answered, and the strongest work in the field is explicit about setting that question aside.
Later anthropological fieldwork extended the comparison well beyond the literate world traditions Heiler worked from, documenting prayer forms in oral traditions his typology had not accounted for, and the discipline today generally treats his categories as a useful starting map rather than a final, complete classification.