Mandukya Karika, verse 1.15

Sanskrit text, IAST transliteration and English translation

अन्यथा गृह्णतः स्वप्नो निद्रा तत्त्वमजानतः ।
विपर्यासे तयोः क्षीणे तुरीयं पदमश्नुते ॥ १५ ॥

anyathā gṛhṇataḥ svapno nidrā tattvamajānataḥ |
viparyāse tayoḥ kṣīṇe turīyaṃ padamaśnute || 15 ||

15. Svapna or dream is the wrong cognition of Reality. Nidrā or sleep is the state in which one does not know what Reality is. When the erroneous knowledge in these two disappears, Turīya is realized.

Shankara Bhashya (commentary)

When is one established in Turīya? It is thus replied: During the states of dream and waking when one wrongly cognizes Reality like the perception of the snake in the place of the rope, he is said to be experiencing dream.¹ Nidrā or sleep,² characterised by the ignorance of Reality, is the common feature of the three states. Viśva and Taijasa, on account of their having the common features of Svapna (dream) and Nidrā (sleep), form a single class. That Nidrā (sleep) which is characterised by the predominance of wrong apprehension (of Reality) constitutes the state of inversion which is Svapna (dream). But in the third state, Nidrā (sleep), alone, characterised by the nonapprehension of Reality is the only inversion. (This forms the second or the other class implied in the text which speaks only of dream and sleep as covering the three states.) Therefore when these two classes of the nature of effect and cause, characterised by the mis-apprehension and non-apprehension respectively (of Reality), disappear by the destruction of the inversion characterised by effect and cause, by the knowledge of the nature of the Highest Reality, then one realises Turīya which is the goal. Then one does not find in Turīya this condition, the characteristics of which are these two (effect and cause), and one thus becomes firm in the Highest Reality which is Turīya.

Anandagiri Tika (glossary)

¹ Dream—Svapna includes dream and waking states, ordinarily so called, as in both the states there is a wrong apprehension of Reality. The inversion (absence of the Knowledge of Reality) which is the characteristic of sleep is found in dream and waking also. In other words, this is the common characteristic of all the three states.

² Nidrā—Nidrā includes the three states of waking, dream and sleep, ordinarily so-called, as all the three states are characterised by the absence of the Knowledge of Reality. The inversion, characteristic of Nidrā, is the non-apprehension of Reality and this is the only feature of Prājña. But Svapna (dream) including the waking state also is characterised by both non-apprehension and mis-apprehension of Reality.