From the multitude of deity names occurring in early-colonial sources (and especially in the medical 'Rituals of the Bacabs'), about twenty have been linked to deity figures from the three Postclassic codices and their correspondences in the corpus of Classic ceramic representations; these have been assigned letter names (Schellhas-Zimmermann-Taube classification). The codices demonstrate that deities were permanently being arranged and rearranged according to cultic criteria which usually are not immediately accessible to us. Moreover, Maya deities typically operate within various fields, changing attributes accordingly.