Seer = Seeing = Seen
An interesting excerpt from "I Am That" by Nisargadatta Maharaj:
Q: You say that the seer, seeing and the seen are one single thing, not three. To me the three are separate, I do not understand.
M: Look closely and you will see that the seer and the seen appear only when there is seeing. They are attributes of seeing. When you say ‘I am seeing this’. ‘I am’ and ‘this’ come with seeing, not before. You cannot have an unseen ‘this’ nor an unseeing ‘I’ am’.
Q: I can say: ‘I do not see’.
M: The ‘I am seeing this’ has become ‘I am seeing my not seeing’, or ‘I am seeing darkness’. The seeing remains. In the triplicity: the known, knowing and the knower, only the knowing is a fact. The ‘I am’ and ‘this’ are doubtful. Who knows? What is known? There is no certainty, except that there is knowing.
Q: Why am I sure of knowing, but not of the knower?
M: You can be aware of the knowing but not of a knower. Knowing is a reflection of your true nature along with being and loving. The knower and the known are added by the mind. It is in the nature of the mind to create a subject-object duality, where there is none.