The word fornication occurs once in the works of Spanish mystic Juan de la Cruz, but it occurs in a pivotal moment, as one of the three “spirits” sent by God during the noche oscura, the purgative process described by Juan’s poetic and prose works of the same name. Lust and romance seem to have a special, uncelebrated place in the dark night mostly overlooked by scholars. The topic of fornication is more than philological curiosity; its combination of literal and metaphorical seems to be the best heuristic to Juan’s mystical writing. The significance of fornicación becomes evident in light of the context of Juan’s writing: the Spanish contemplative tradition, biblical texts which influenced Juan, and fifteenth-century courtly love poetry. The three spirits of the dark night, including fornication are those areas of self that the spiritual aspirant cannot fix alone. Juan’s concept of the automatic nature of the purgation of the dark night refers to cognitive processes beyond will and reason. Both Juan’s poetic text and its prose explication signal the mystical connection between literal and metaphorical, the physical and spiritual.