The paper reconstructs the internal doctrinal logics which forced Descartes to create the own theory of ego cogitans as a cogitative substance. Since the res cogitans had been created ad imaginem & similitudinem Dei, from the very beginning it appears as a complex of paradoxical ruptures caused by the contradistinction between the limited and the eternal: 1) between the freedom of res cogitans and Divine predestination; 2) between the limitedness of the individual intelligence and the real apodictic character of truths which it perceives; 3) between the essential imperfection of ego and its intrinsic understanding of the Divine perfection. The discrepancy between cogito as an individual act of thinking and apodictic character of its patency is just one of many paradoxes. The axiomatics of the Descartes’s metaphysics envisages the real presence of eternal God in the structure of created individual ego and, correspondingly, «normality» of statements, which look paradoxical from the point of abstract rationality: God guarantees things that separate ego is incapable for. The author also criticizes reading back into Descartes the modernized notions of “substance”, “subject” and “consciousness”.