The Japanese kanji for 'jo' in ichijo and sanjo refers to the vehicle which leads all living things to attain satori (the term used to mean enlightenment in Japanese Buddhism); the "Hokekyo" (Lotus Sutra), which is the primal scripture of the Tendai sect, teaches that the sanjo in traditional Buddhist scriptures is the means of leading the ichijo, based on ichijo-setsu (doctrine that only one teaching, usually the Lotus Sutra, can lead to enlightenment), which teaches that all living things can attain Buddhahood in the end.
一乗・三乗の「乗」とは衆生を乗せて仏の悟りに導く乗り物であり、天台宗の根本経典である『法華経』では、一切衆生の悉皆成仏（どのような人も最終的には仏果（悟り）を得られる）を説く一乗説に立ち、それまでの経典にあった三乗は一乗を導くための方便と称した。