Brahma Sutras – According to Shankara 2-3-12
Topic 12 - The nature of the individual soul is intelligence
ज्ञोऽत एव ॥ १८ ॥
jño’ta eva || 18 ||
jñaḥ—Intelligence; ata eva—for this very reason.
18. For, this very reason (i.e. that it is not created), (the individual soul is) intelligence (itself).
The Vaiśeṣikas say that the individual soul is not intelligent by nature, for it is not found to be so in the state of deep sleep (Suṣupti) or of swoon. It is only when the soul comes to the conscious plane and unites with the mind that it becomes intelligent.
This Sutra refutes such a possibility, for it is the intelligent Brahman Itself that, being limited by the Upādhis (limiting adjuncts), the body etc., manifests as the individual soul.
Therefore intelligence is its very nature, and is never altogether destroyed, not even in the state of deep sleep or swoon:
“That it does not see in that state is because although seeing then, it does not see; for the vision of the witness can never be lost, because it is immortal. But there is not that second thing separate from it which it can see” (Brih. 4. 3. 23).
Therefore it is not true that its intelligence is lost, for it is impossible. It does not in reality lose its power of seeing; it does not see only because there is no object to see.
Were intelligence actually non-existent then, who would be there to say that it did not exist? How could it be known?
Moreover, he who says that he did not know anything in deep sleep, must have been existent at that time. Otherwise how could he remember the condition of that state?
Hence the intelligence of the Self is never lost under any condition.