Yoga Sutra 1.05 the mental processes are of five kinds

The mental processes are of five kinds; they are tainted or pure

The mental processes are to be inhibited, though they are many. In the extraverted state, Puruṣa conforms to them as has been explained. Why are they to be inhibited? The sūtra says, They are tainted or pure.

(Opponent) They are too many to be inhibited.

(Answer) To this the sūtra says, They are of five kinds. Though there is an infinity of them, tainted and pure, still they are of only five kinds, of five classes, five groups. Only by recourse to practice and detachment, which oppose them en bloc, does inhibition succeed; their mere number does not make inhibition impossible, though there is no effective means of inhibiting them one by one.

The tainted are caused by the five taints, for mind, impelled by Ignorance and the other four taints, again and again invites the self, and they become the seedbed for the growth of the accumulated karma seed-stock. Karmas are favourable, unfavourable, and mixed, and they are referred to as karma seed-stock inasmuch as they have a latent drive towards producing fruits. The mass of them is held together, each sometimes predominating and sometimes auxiliary to others. With that mass of karma seed-stock as cause, Ignorance and the other taints become the seed-bed for tainted mental processes. When these last appear, the karma seed-stock is near to ripening.

The pure are the field of Knowledge, they are the seats (āspada) of Knowledge. They oppose involvement activity of the saṃskāra-s with the guṇa-s sattva, rajas, and tamas. It is because they are directed towards the field of Knowledge that they are pure, since Knowledge brings about release (apavarga).

When pure thoughts arise in the midst of a mass of tainted ones, do they themselves become tainted – like drops of water thrown into a pot of milk? And do the tainted, caught in a current of pure ones, themselves become pure? What would follow if they did? If pure ones that happened to be in a current of tainted ones were to become tainted, it would mean that memory, which conforms to the saṃskāra of the thought which produced it, and on whose accuracy life in the world depends, would be unreliable, for the thoughts would be inherently uncertain. So he says In gaps between tainted ones, there are pure ones which remain pure, and in gaps between pure ones, the tainted are still tainted. And this being so, it is only by mental processes (vṛtti) that saṃskāra-s corresponding to them are produced. Though the taints and so on do set up saṃskāra-s, it happens only through the medium of mental processes, and this is the force of the word only. And by saṃskāra-s, mental processes corresponding to them are produced; so the wheel of process and saṃskāra continuously incessantly revolves.

Such is the mind, characterized by having processes and saṃskāra-s each causing the other; but when it has given up its involvement (adhikāra) when the activity caused by Ignorance has ceased and it rests in the causal state alone it rests in the likeness of self (ātman) in the likeness of Puruṣa, as pure Knowledge alone, for a time conforming to the remainder of the saṃskāra-s which have already begun to function (prārabdha), or else dissolves when the saṃskāra-s have come to an end.