Ego and Self by C.G. Jung

C.G. Jung writes in his Memories, Dreams and Reflections:

Somewhere deep in the background I always knew that I was two persons. One was the son of my parents, who went to school and was less intelligent, attentive, hard-working, decent, and clean than many other boys. The other was grown-up -- old, in fact -- skeptical, mistrustful, remote from the world of men, but close to nature, the earth, the sun, the moon, the weather, all living creatures, and above all close to the night, to dreams, and to whatever "God" worked directly in him. I put "God" in quotation marks here. For nature seemed, liked myself, to have been set aside by God as non-divine, although created by Him as an expression of Himself. Nothing could persuade me that "in the image of God" applied only to man. In fact, it seemed to me that the high mountains, the rivers, the lakes, trees, flowers, and animals far better exemplified the essence of God than men with their ridiculous clothes, their meanness, vanity, mendacity, and abhorrent egotism -- all qualities with which I was only too familiar from myself, that is, from personality No. 1, the schoolboy of 1890. Besides his world there existed another realm, like a temple in which everyone who entered became transformed and suddenly overpowered by a vision of the whole cosmos, so that he could only marvel and admire, forgetful of himself. Here lived the "Other" who knew God as a hidden, personal, and at the same time suprapersonal secret. Here nothing separated man from God; indeed, it was as though the human mind looked down upon creation simultaneously with God.

What I am here unfolding, sentence by sentence, is something I was then not conscious of in any articulate way, though I sensed it with an overpowering premonition and intensity of feeling. At such time I knew that I was worthy of myself, that I was my true self. As soon as I was alone, I could pass over into this state. I therefore sought the peace and solitude of this "Other", personality No. 2.

The play and counterplay between personalities No. 1 and No. 2, which has run through my whole life, has nothing to do with a "split" or dissociation in the ordinary medical sense. On the contrary, it is played out in every individual. In my life, No. 2 has been of prime importance, and I have always tried to make room for anything that wanted to come to me from within. He is a typical figure, but he is perceived only by the very few. Most people's conscious understanding is not sufficient to realise that he is also what they are.

Jung went on later to define his "personality No. 2" as the Self, the part that apprehended "the One", the oneness of all living creatures and the universe. Whereas the "personality No. 1", the ego, perceived the objective world which arises through the process of duality, "the Two".