Tranquility (mental elements 34 and 35, Tr1-Tr2)
Tranquility is the phenomenon that reduces activity. In a way, it makes the mind inactive just as a tranquilizer would make a wild animal inactive. This does not mean the mind becomes slack or dull. It simply indicates the state of mind free of activities such as discursive thinking, agitation, restlessness, worry, distress, stress, and so on. It makes the mind calm and still by crushing these activities. In this sense, tranquility is the opposite of agitation, disturbances, distress, and even stress. It is an essential wholesome element, always present in some degree in all wholesome states of consciousness.
Experienced meditators are aware of the extraordinary delight that results from tranquility of body and mind. This delight is truly superhuman. When tranquility is perfected, delight can also be transcended while in deep concentration, leading to spiritual bliss.
Tranquility is a power element like mindfulness, because it awakens the mind for perfection, assists in bringing mastery to the mind, and makes the mind prone to enlightenment.