alternatio

Alternatio is a Latin noun meaning alternation, interchange, or the act of alternating between two or more elements. The term appears in historical sources to denote a process in which different elements take turns or alternate in a sequence. In scholarly use, alternatio is typically field-specific and its exact sense depends on the discipline involved.

In music, alternatio (often written alternatim) refers to a practice in medieval and early modern Western liturgical performance. In this context, sections of chant and polyphony are presented in alternating fashion. A chant might be sung in its monophonic form, with portions replaced by or answered by polyphonic settings, or the organ or choir might alternate with the chant at prescribed points. The practice was common from roughly the 12th to the 17th centuries and influenced how many liturgical melodies were elaborated, balancing the integrity of the chant with expanded musical texture.

Beyond music, alternatio appears in Latin scholastic, rhetorical, and textual contexts to indicate alternation between positions, readings, or elements within a discourse. In these uses, the term signals a switch or interchange that serves the argument, analysis, or transmission of a text. Today, alternatio is mainly encountered as historical terminology rather than as a current technical term, with its precise meaning shaped by the particular field and period of study.