ichinen

Ichinen is a Japanese term written with the characters 一念 and generally understood to mean “one thought” or “one moment.” The word combines ichi (one) and nen (thought, mind, or moment) and is used primarily within Buddhist contexts to describe the immediacy of mental activity.

In East Asian Buddhism, ichinen is most closely associated with the Tendai and Nichiren schools. It serves as a foundation for the doctrine of ichinen sanzen, commonly rendered as “three thousand realms in a single moment.” This concept posits that within a single instant of thought, a wide and interdependent range of phenomena (the ten realms) can be encompassed and mutually interpenetrate. The doctrine is used to illustrate how the mind and the world are interconnected and how enlightenment can be realized within the immediacy of a moment.

Related expressions include ichinen hokki (一念発起), which means to make a vow or resolve in a single thought, and is often cited in practice and sermons as an exhortation to immediate action or commitment. While ichinen is a technical term in doctrinal texts, it also appears in translations and scholarly discussion of East Asian Buddhist philosophy to convey the idea of consciousness and reality unfolding in a single instant.

Outside scholarly or religious discourse, ichinen is uncommon in everyday Japanese, where more ordinary words would typically be used to express notions of time or mental activity.