Though as a distinct way of practice (s. samatha-yānika), it aims at the attainment of the meditative absorptions (jhāna, q.v.), a high degree of tranquil concentration (though not necessarily that of the absorptions) is indispensable for insight too.
It is the one-pointedness and non-distraction of the mind due to freedom from desire (renunciation) ... to freedom from ill-will ... to the perception of light (s. aloka-saññā) ... to non-distraction ... to the defilling of phenomena ... to knowledge, gladness, the 8 attainments, the [[10 kasinas)], the 10 recollections, the 9 cemetery contemplations, the 32 kinds of respiration-mindfulness ... the one-pointedness and non-distraction of the mind of one contemplating abandonment (relinquishment) while inhaling and exhaling (s. ānāpānasati).
"The power of tranquillity consists of the freedom from perturbation; in the 1st absorption, from the 5 hindrances (nīvarana, (q.v.); in the 2nd absorption, from thought-conception and discursive thinking; ...
in the sphere of neither-perception-nor-non-perception it consists of the freedom from perturbation by the perception of the sphere of nothingness (s. anupubbanirodha), which is no longer agitated and irritated by defilements associated with restlessness, nor by the groups of existence" (Pts.M. 1. p. 97)
(2) 'Insight' (s. vipassanā) is the penetrative understanding by direct meditative experience of the impermanency, unsatisfactoriness and impersonality of all material and mental phenomena of existence.
What now is the power of insight? It is the contemplation of impermanency (aniccānupassanā), of misery (dukkhanupassanā), impersonality' (anattānupassanā), of aversion (nibbidanupassanā), detachment (virāganupassanā), extinction (nirodha), ahandonment (patinissagga), with regard to corporcality, feeling, perception, mental formations and consciousness....
That in contemplating the impermanency one is no more agitated by the idea of grasping ... no more by ignorance and the defilements associated therewith and no more by the groups of existence: this is called the power of insight" (Pts.M. p. 97).
All ignorance is abandoned" (A. II, 2.7).
There is a method of meditative practice where, in alternating sequence, tranquillity-meditation and insight-meditation are developed.
He who undertakes it, first enters into the 1st absorption.
In this way, he passes from one absorption to the next, until at last, during a moment of insight, the intuitive knowledge of the path (of Stream-entry, etc.) flashes forth - See A. IV, 170; A.IX, 36; Pts: Yuganaddha Kathā.