천태종 (天台宗)의 교의 (敎義)로 유문 (有門), 공문 (空門), 역유역공문( 亦有亦空門), 비유비공문 (非有非空門)을 말함

Four paths of perfect or universal teaching: They are the path of existence, the path of emptiness, the path of non-dualistic Middle Way view of being and non-being or emptiness, and the path of non-dualistic Middle Way view of neither being nor non-being of things.