Semah is not one dance. There are many named forms, differing by region and by lineage, each with its own music, tempo and sequence of movement, and dedes and zakirs know which belongs where. The best known is the semah of the forty, which enacts a foundational Alevi narrative of an assembly of forty saints, and it is the one most often performed when the practice is shown to outsiders.
Inside the cem the semah has a fixed place. The cem is built from a set of named services, and semah is one of them, following others in an order the dede who leads the ritual maintains. Participants turn with palms held in a particular relation, one hand receiving and one giving, and the movement is generally slow before quickening. The music is the zakir's, on the saz, and the nefes he sings during it belongs to the same repertory as the rest of the service.
The practice has moved a long way outside the cem in the last fifty years. Alevi associations in Turkish cities and in the European diaspora perform semah at cultural festivals, on television and at political commemorations, and folkloric ensembles have staged it. Opinion inside the community is divided about that. Some hold that visibility has protected a tradition long suppressed and misdescribed, and UNESCO's inscription of the ritual in 2010 is cited on that side. Others hold that a service lifted out of the cem and put on a stage stops being what it was. Both positions are widely held and the argument is not settled.