There are several theories as to the derivation of the term Sanmon, including the following: that the term symbolizes the gates one has to pass through in order to be delivered from the three evil passions of avarice, anger and stupidity; or that the term symbolizes the gates to the three paths to Buddhahood of Shomon (learning), Engaku (self-attained enlightenment) and Bosatsu (bodhisattva).
三門の名称の由来は、貪・瞋・痴の三煩を解脱する境界の門、声聞・縁覚・菩薩の三乗が通る門などの説がある。