four forms of meditation ［四種三昧］ ( shishu-sammai or shishu-zammai): Also, four kinds of meditation or four kinds of samādhi. Four methods of meditation described in T’ien-t’ai’s Great Concentration and Insight. T’ien-t’ai (538–597) classified the various types of meditation referred to in the Buddhist sutras into four comprehensive categories: (1) constant sitting meditation, in which one engages in seated meditation for ninety days; (2) constant active meditation, in which one meditates while walking around a statue of the Buddha in a monastery for ninety days; (3) half-active and half-sitting meditation, in which one engages in the two practices of seated meditation and of walking around a meditation platform. (This third practice is further divided into that based upon the Great Correct and Equal Dhāranī Sutra and that based on the Lotus Sutra. The former practice is carried out for seven days, and the latter, for twenty-one days); and (4) meditation in an unspecified posture for an unspecified period, in which one practices meditation of an unspecified length of time or form. All meditations not covered in the first three categories are included in the last.