The Vedanta Sutras with the Commentary by Ramanuja

For common observation shows that the consciousness of one person may become the object of the cognition of another, viz. of an inference founded on the person’s friendly or unfriendly appearance and the like, and again that a person’s own past states of consciousness become the object of his own cognition–as appears from judgments such as ‘At one time I knew.’ It cannot therefore be said ‘If it is consciousness it is self-proved’.