The Difference Between Meditative Concentration (Samādhi) and Tranquility

Samādhi includes stillness; stillness is the initial stage of samādhi, the initial form of its manifestation. First, the body becomes still and unmoving; next, the mind's thoughts settle into quietude. As it develops further, samādhi deepens—it is no longer merely the stillness of body and mind; some dharmas must disappear, and the mind's thoughts become even more focused and unified, until even the thoughts themselves vanish. From the second dhyāna onward, the five sense consciousnesses disappear; from the fourth dhyāna onward, breathing, pulse, and heartbeat cease and disappear. The deeper the samādhi, the fewer dharmas appear. Whether many or few dharmas appear is determined by the manas; the depth of samādhi depends on whether the manas has been subdued, on the question of how many dharmas the manas engages with and clings to.