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 favours 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. ~Carl Jung, CW 9ii, Para 3