threefold contemplation in a single mind ［一心三観］ ( isshin-sangan): Also, threefold contemplation. A method of meditation formulated by T’ien-t’ai (538–597) in Great Concentration and Insight, intended to enable one to perceive the unification of the three truths of non-substantiality, temporary existence, and the Middle Way.
While the concept of the unification of the three truths constitutes the doctrinal core of T’ien-t’ai teachings, threefold contemplation in a single mind constitutes the core of T’ien-t’ai practice. T’ien-t’ai doctrine regards each phenomenon as a perfect unity of the three truths and sets forth the threefold contemplation in a single mind as the practice by which one attains insight into this perfect unity. This contemplation involves perceiving the three truths as simultaneously and perfectly integrated and interfused in each phenomenon. By doing so, one is said to rid oneself of the three categories of illusion and acquire at once the three kinds of wisdom—the wisdom of the two vehicles, the wisdom of bodhisattvas, and the Buddha wisdom. T’ien-t’ai also describes a single mind as comprising the three thousand realms. In this sense, threefold contemplation in a single mind is equal to observing a single moment of life and seeing the three thousand realms within it. At the same time, one perceives that all phenomena consist of the three thousand realms.