Visuddhi: 'purification', purity. The '7 stages of purification' satta-visuddhi form the substructure of Upatissa's Vimutti-Magga The path To Freedom, preserved only in Chinese, as well as of Buddhaghosa's monumental work, Visuddhimagga The path of Purification, based on the former work.
The only place in the Canon where these 7 kinds of purification are mentioned is M. 24,,The Simile of the Stage-coach; see: 'path', §64, wherein their purpose and goal are illustrated. There it is said that the real and ultimate goal does not consist in purification of morality, or of mind, or of view, etc., but in total deliverance and ceasing. Now, just as one mounts the first coach and travels to the second coach, then mounts the second coach and travels with it to the third coach, etc., in exactly the same way the goal of I the purification of morality sila-visuddhi is II the purification of mind citta-visuddhi its goal: III the purification of view ditthi-visuddhi its goal: IV the purification by overcoming doubt kankhāvitarana-visuddhi its goal: V the purification by knowledge and vision of what is path and not-path maggāmagga-ñānadassana-visuddhi its goal: VI the purification by knowledge and vision of the path-progress patipadā-ñānadassana-visuddhi; its goal: VII the purification of knowledge and vision ñānadassana-visuddhi but the goal of this purification is deliverance freed from all clinging.
I: Purification of morality sīla-visuddhi consists of the 4-fold purity of morality catu-pārisuddhi-sīla namely: restraint with regard to the Disciplinary Code pātimokkhasamvara-sīla sense-restraint indriysamvara-sīla purity of livelihood ājīvapārisuddhi-sīla morality with regard to the 4 requisites paccaya-sannissita-sīla Vis.M XVIII. On these 4 terms, see: sīla- In the case of a layman, it entails the observance of whatever moral rules 5 or more he has taken upon himself.
II: Purification of mind citta-visuddhi is a name for the 8 attainments = absorptions: jhāna, as well as for neighbourhood-concentration upacāra-samādhi, see: samādhi. ib..
III: By purification of view ditthi-visuddhi is meant the understanding, according to reality, of mind and materiality nāma-rūpa... which is founded on unconfusedness understanding as base, and which in many ways determines mind and materiality after overcoming all belief in a persollality attā self, ego..; ib..
IV:By purification by overcoming doubt kankhā-vitarana-visuddhi is meant the understanding which, by grasping the conditions of this mind and materiality, has escaped from all doubt with regard to the 3 times past, present, future.; ib. XIX
V: By purification by knowledge and vision of what is path and not-path maggāmagga-ñānadassana-visuddhi is meant that understanding which knows the right path from the wrong path: 'This is the right path, that the wrong path.'ib. XX
In order to attain this 5th stage of purification, one at first should develop methodical insight naya-vipassanā i.e. through contemplation of the 5 groups of existence khandha. For whosoever does not yet possess a perfectly developed insight, to him such phenomena as effulgence of light, etc. see below, arising during insight, may become impediments in the 3 kinds of full understanding here considered see: pariññā
'As soon as the many ways and characteristics of the 4 Truths sacca and the dependent origination paticcasamuppāda have become clear to the meditating disciple, he says to himself: Thus do these things never before arisen arise, and having arisen they disappear again. Thus do the constructions of existence ever and again arise as something quite new. But not only are they something new, they are moreover also of limited duration, like a dew-drop at sunrise, like a bubble, like a line drawn with a stick in the water, like a mustard seed placed on the point of an arrow, or like a flash of lightning. Also as something unsubstantial and empty do they appear, as jugglery, as a mirage. Merely something subject to vanishing arises, and having arisen disappears again.
During such insight practice, however, may arise the 10 imperfections or defilements of insight vipassanūpakkilesa effulgence of light obhāsa knowledge ñāna rapture pīti tranquillity passaddhi happiness sukha determination adhimokkha energy paggaha awareness upatthāna delight nikanti - See Vis.M XX, 105f. App..
Excepting the last one, 'delight', they are not imperfections or defilements in themselves, but may become a basis for them through the arising of pride or delight or by a wrong conclusion that one of the Noble paths has been attained. He, however, who is watchful and experienced in insight practice, will know that these states of mind do not indicate attainment of the true path, but are only symptoms or concomitants of insight meditation.
Thus far the meditating disciple has determined 3 of the truths, namely while determining the material and mental phenomena he has, through purification of view ditthi-visuddhi determined the 'truth of suffering'. While grasping the conditions he has, through purification by overcoming doubt kankhā-vitarana-visuddhi determined the 'truth of the origin of suffering'. While determining the right path, he has, through purification by knowledge and vision of what is path and not-path maggāmagga-ñānadassana-visuddhi, determined the 'truth of the path' leading to the ceasing of suffering
VI: Purification by knowledge and vision of the path-progress patipadā-ñānadassana-visuddhi is the insight perfected in 8 kinds of knowledge, together with the 9th knowledge, the 'knowledge adapting itself to truth'.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.