There are anecdotal reports of people willingly being bound or whipped, as a prelude to or substitute for sex, during the 14th century. The medieval phenomenon of courtly love in all of its slavish devotion and ambivalence has been suggested by some writers to be a precursor of BDSM. Some sources claim that BDSM as a distinct form of sexual behavior originated at the beginning of the 18th century when Western civilization began medically and legally categorizing sexual behavior (see Etymology).