Samadhi and dhyana are to a great extent synonymous and interchangeable, but strictly samadhi is a psychological state realised by the exercise of dhyana. The latter is the process and the former is the goal. The Buddhist scriptures make reference to so many samadhis, and before delivering a sermon the Buddha generally enters into a samadhi,[f41] but never I think into a dhyana. The latter is practised or exercised. But frequently in China dhyana and samadhi are combined to make one word, _ch‘an-ting_;[2.3] meaning a state of quietude attained by the exercise of meditation or dhyana. There are some other terms analogous to these two which are met with in Buddhist literature as well as in other Indian religious systems. They are _Saṁpatti_ (coming together), Samāhita (collecting the thoughts), Śamatha (tranquillisation), _Cittaikāgratā_ (concentration), _Dṛishta-dharma-sukha-vihāra_ (abiding in the bliss of the Law perceived), _Dhāraṇi_ or _Dhāraṇa_ (abstraction), etc. They are all connected with the central idea of dhyana, which is to tranquillise the turbulence of self-assertive passions and to bring about a state of absolute identity in which the truth is realised in its inwardness, that is, a state of Enlightenment. The analytical tendency of philosophers is also evident in this when they distinguish four or eight kinds of dhyana.[f42] The first dhyana is an exercise in which the mind is made to concentrate on one single subject until all the coarse affective elements are vanished from consciousness except the serene feelings of joy and peace. But the intellect is still active, judgment and reflection operate upon the object of contemplation. When these intellectual operations too are quieted and the mind is simply concentrated on one point, it is said that we have attained the second dhyana, but the feelings of joy and peace are still here. In the third stage of dhyana, perfect serenity obtains as the concentration grows deeper, but the subtlest mental activities are not vanished and at the same time a joyous feeling remains. When the fourth and last stage is reached, even this feeling of self-enjoyment disappears, and what prevails in consciousness now is perfect serenity of contemplation. All the intellectual and the emotional factors liable to disturb spiritual tranquillity are successively controlled, and mind in absolute composure remains absorbed in contemplation. In this there takes place a fully-adjusted equilibrium between Samatha and Vipasayana, that is, between tranquillisation or cessation and contemplation. In all Buddhist discipline this harmony is always sought after. For when the mind tips either way, it grows either too heavy (_styānam_) or too light (_auddhatyam_), either too torpid in mental activity or too given up to contemplation. The spiritual exercise ought to steer ahead without being hampered by either tendency, they ought to strike the middle path.