Infinite Life Sutra in the context of "Primal Vow"

In Pure Land Buddhism, the Original Vow, or Fundamental Vow (本願, hongan) refers to a forty eight part vow that Amitābha Buddha made (long ago when he was a bodhisattva named Dharmakara). The term is often used to refer solely to the 18th part of the vow in particular (sometimes just called the 18th vow), which is very important for Pure Land Buddhist doctrine, especially in Japanese Buddhism.

The term comes from the Sanskrit pūrva-praṇidhāna, which means Past vow or Previous Vow. This term originally referred to any bodhisattva vows made by any bodhisattva in a past life, which retain a special spiritual power even after Buddhahood. Thus, the term can also refer to the past vows of other figures, such as is the twelve vows of Medicine Master Buddha. In Pure Land Buddhism however, the term specifically refers to the vow of Amitābha Buddha (Jp: Amida Butsu) found in the Infinite Life Sutra.