A legend (Latin, legenda, "things to be read") is a narrative of human actions that are perceived both by teller and listeners to take place within human history and to possess certain qualities that give the tale verisimilitude. Legend, for its active and passive participants includes no happenings that are outside the realm of "possibility", defined by a highly flexible set of parameters, which may include miracles that are perceived as actually having happened, within the specific tradition of indoctrination where the legend arises, and within which it may be transformed over time, in order to keep it fresh and vital, and realistic. A majority of legends operate within the realm of uncertainty, never being entirely believed by the participants, but also never being resolutely doubted. The Brothers Grimm defined legend as folktale historically grounded. A modern folklorist's professional definition of legend was proposed by Timothy R. Tangherlini in 1990: