This paper focuses on Freud’s concept of “historical truth”. Exploring Freud’s Moses, it objects to Karsenti’s (2012) recent analysis by putting forth the central role of psychosis in the clinical understanding of the monotheistic phenomenon. Bearing in mind Freud’s equation of monotheism with a delusional construction is the only way to understand the kernel of truth which lies within monotheism. Thus Moses’ novelty is not to be found in the concept of historical truth, already at work in The future of an Illusion, but in the development made possible by its connection with the psychoanalytic approach to psychosis – Freud’s own understanding of the mono- in monotheism. Only the “literalism of psychosis”, by accounting for the acted repetition of the original murder of the primal father, can shed light on Freud’s realism.