How to talk about origins? How can we say what was the birth of the universe, that of man, that of society? From Timaeus to Critias, the answer does not vary: it is to a discourse which constitutes its object that the explanatory task falls. On the one hand, the cosmology of Timaeus which seeks the conditions for knowledge of the sensible world. On the other, the story of the war which opposed ancient Athens to Atlantis, recounted twice (Timaeus, Critias); or how a myth is born that is always present in our imagination as modern men. Here Plato tells stories and establishes the scientific method. Poet or philosopher? He doesn't choose. “Having been endowed with the living mortals and immortals and having thus reached its fullness, our world was born, a visible living including the visible living, a sensitive god, the image of an intelligible god, very great, very good, very beautiful, and very perfect, a unique sky which is the only one of its race. »