Mandukya Karika, verse 1.12

Sanskrit text, IAST transliteration and English translation

नाऽऽत्मानं न परंश्चैव न सत्यं नापि चानृतम् ।
प्राज्ञः किंचन संवेत्ति तुर्यं तत्सर्वदृक्सदा ॥ १२ ॥

nā''tmānaṃ na paraṃścaiva na satyaṃ nāpi cānṛtam |
prājñaḥ kiṃcana saṃvetti turyaṃ tatsarvadṛksadā || 12 ||

12. Prājña does not know anything of the self or the non-self nor truth nor untruth. But Turīya is ever existent and ever all-seeing.

Shankara Bhashya (commentary)

How is it that Prājña is conditioned by cause? And how is it, again, that the two conditions of non-apprehension and mis-apprehension of Reality do not exist in Turīya? It is because Prājña does not, like Viśva and Taijasa, perceive anything of the duality,¹ external to and other² than itself and born³ of the cause known as Avidyā. Therefore it is conditioned by darkness characterised by non-apprehension of Reality which is the cause of mis-apprehension. As Turīya exists always, ever all-seeing⁴, on account of the absence of anything other than Turīya, it is never associated with the causal condition characterised by non-apprehension of Reality. Consequently mis-apprehension of Reality winch is the result of non-apprehension is not found in Turīya. For, it is not possible to find in the sun, whose nature is to be ever-luminous, anything contrary to light, viz., darkness, or any other light different from itself. The Śruti also says: “The Knowledge of the seer is never absent.” Or the phrase may be explained thus: Turīya may be designated as ever all-seeing because it subsists in all, in dream and waking states and all the seers that cognize them (in those states) are Turīya alone. This is also borne out by the following Śruti passage, “There is no seer other than this.”

Anandagiri Tika (glossary)

¹ Duality— This dual world is true from empirical standpoint. Prājña does not perceive it.

² Other than, etc—Prājña does not see the external world or the non-self. Therefore it does not see itself. Ego can be cognized only in relation to the non-ego.

³ Born, etc.—That is untruth. It is because Prājña does not see the unreal external world produced by Avidyā, therefore it is not aware of mis-apprehension.

⁴ Ever all-seeing—It is because it exists in the seers and the things seen in both the states, it is ever all-seeing.