In this paper we claim that psychosis is not just a category of psychopathology, but rather a way of mental functioning which belongs to the very early days of our lives. We tried to put light on the path which begins with only the bodily sensations which is the trade mark of otistic-contigious position, towards the establishment of the psyche and the beginning of symbolization. We emphasized the fundamental role of essential depression for the foundation of the psychic “I”, in other words the “ego”. We also tried to explain the fundamental movement of the psyche which is the movement of oscillation, and show how it functions between otistic-contigious and paranoid schizoid positions just like Bion who has suggested an oscillatory movement between PS↔D. In our view, psychopathology appears if the oscillatory movement is disturbed and the development comes to a halt.