Yoga Sutra 2.06 purusa is the power of seer buddhi is the power of seeing

Sūtra II.6

The single selfhood, as it were, of the powers of seer and seeing is I-am-ness

Now the illusion called I-am-ness. Puruṣa is seer, his seeing being awareness, and he is a power; seeing, in the sense that by it something is seen, is also a power, whose nature is the determination of things by the mind (antaḥkaraṇa). Of these two powers of seer and seeing, whose natures are awareness and mental determination, the single selfhood as it were: single selfhood is the state where it is both one and this self; the word iva, as it were, shows that there is in fact absolute distinction between them. The taking on of a single nature as it were is called the taint of I-am-ness. That I-notion (aham-pratyaya) in which the distinction between mind (citta) and Puruṣa is not perceived, the notion ‘he is this I’, is the taint called technically I-am-ness. It was said earlier that what is called Ignorance is only illusory seeing, the conviction of self in the not-self of mind (antaḥkaraṇa) which is an accessory to Puruṣa. But here it is specified as I-am-ness, the seeing of mind (buddhi) and Puruṣa as not distinct, which as it were conflates them into a single nature.

On this it is said: When there comes about a failure, as it were, to distinguish between the experiencer (bhoktṛ) and what is experienced (bhogya) which are utterly distinct and nothing to do with each other, that is the condition for experience. The meaning is, that the cause of experience is the taint called I-am-ness. When there is an I-notion, there comes about the relation with pleasure, pain, etc., in the form ‘I am pleased’ or ‘I am pained’, and this is why it is so.

But when the true nature of the two mind (buddhi) and Puruṣa is recognized, in the discriminative awareness of their true nature in the form ‘not I and mine’ that is Transcendental Aloneness (kaivalya) with no mingling at all. Then how could there be experience? The cause is the undiscriminated I-notion taken as self, and the effect is experience; and when that cause is not there, neither is experience.

For unless sentience had been projected (adhyāropya) into the mind, there would be no recurrence of the fact of enjoyer or sufferer. The field of the I-notion is the location of the notions of pleasure and pain, and the location of ‘I am an enjoyer’ and ‘I am a sufferer’ is the same. In this way the egoity (ahaṅkāra) called I-am-ness (asmitā) is the cause of experience.

So it has been said: Puruṣa beyond the mind beyond the presence of the mind, distinct from it as being of different qualities, as being other than it. What those differences of qualities are, he explains:

in form by merely conforming to mental processes,

in habitual character by its witnessing of the mind,

in knowledge, as being of the nature of consciousness.

Or on another interpretation,

in form by the fact of its nature of purity and infinity,

in habitual character in that being immutable, it does not dissolve into any cause,

in knowledge in that it is the power-of-consciousness (citi-śakti) by nature.

In these qualities, it is distinct from mind (buddhi).

Then too, the mind is distinguishable from Puruṣa

in form as being essentially pleasure, pain and delusion,

in habitual character as essentially illumination, activity and fixity,

in knowledge as its essence is to determine all.

Not seeing Puruṣa thus distinct in mutually different form, habitual character and knowledge, he will make there in that mind a mental self a notion of self, out of delusion (moha). The seeing of mind and Puruṣa, which are utterly distinct in knowledge and habitual character and form, as inseparate as it were, to that extent illustrates I-am-ness.

But not seeing Puruṣa beyond, he makes in the mind a mental self; this is the Ignorance formerly described. Or if we take it that I-am-ness is a division of Ignorance, then the illustration stands as a whole. It is said that not seeing, he will make (the mental self), and it means that the cause of Ignorance is the failure-to-see the true nature of Puruṣa, and the cause of I-am-ness is the colouring of the mind as both seer and seen. But there is no seeing of Puruṣa himself because he is pure Seer-hood alone.