The ego, as a specific content of consciousness, is not a simple or elementary factor but a complex one which, as such, cannot be described exhaustively.
Experience shows that it rests on two seemingly different bases: the somatic and the psychic.
The somatic basis is inferred from the totality of endosomatic perceptions, which for their part are already of a psychic nature and are associated with the ego, and are therefore conscious.
They are produced by endosomatic stimuli, only some of which cross the threshold of consciousness. A considerable proportion of these stimuli occur unconsciously, that is, subliminally.
The fact that they are subliminal does not necessarily mean that their status is merely physiological, any more than this would be true of a psychic content.
Sometimes they are capable of crossing the threshold, that is, of becoming perceptions.
But there is no doubt that a large proportion of these endosomatic stimuli are simply incapable of consciousness and are so elementary that there is no reason to assign them a psychic nature unless of course one favors the philosophical view that all life-processes are psychic anyway.
The chief objection to this hardly demonstrable hypothesis is that it enlarges the concept of the psyche beyond all bounds and interprets the life-process in a way not absolutely warranted by the facts.
Concepts that are too broad usually prove to be unsuitable instruments because they are too vague and nebulous.
I have therefore suggested that the term “psychic” be used only where there is evidence of a will capable of modifying reflex or instinctual processes.
Here I must refer the reader to my paper “On the Nature of the Psyche,” where I have discussed this definition of the “psychic” at somewhat greater length.
The somatic basis of the ego consists, then, of conscious and unconscious factors.
The same is true of the psychic basis: on the one hand the ego rests on the total field of consciousness, and on the other, on the sum total of unconscious contents.
These fall into three groups: first, temporarily subliminal contents that can be reproduced voluntarily (memory); second, unconscious contents that cannot be reproduced voluntarily; third, contents that are not capable of becoming conscious at all.
Group two can be inferred from the spontaneous irruption of subliminal contents into consciousness. Group three is hypothetical; it is a logical inference from the facts underlying group two. This contains contents which have not yet irrupted into consciousness, or which never will.
When I said that the ego *’rests” on the total field of consciousness I do not mean that it consists of this. Were that so, it would be indistinguishable from the field of consciousness as a whole. The ego is only the latter’s point of reference, grounded on and limited by the somatic factor described above.
Although its bases are in themselves relatively unknown and unconscious, the ego is a conscious factor par excellence. It is even acquired, empirically speaking, during the individual’s lifetime.
It seems to arise in the first place from the collision between the somatic factor and the environment, and, once established as a subject, it goes on developing from further collisions with the outer world and the inner. ~Carl Jung; Aion; Page 5.