[Principles of knowledge of disease Synonyms of Nidana (causative factors) and its types] Hetu, nimitta, ayatana, karta, karana, pratyaya and samutthana are synonyms of nidana (causative factors). Nidana is of three types: Asatmyendriyarthasamyoga (unsuitable contact of sense organs with their objects) Prajnaparadha (intellectual errors or knowingly engaging in harmful activities), and Kala (time, seasonal, temporal factors).