AbstractMarsilio Ficino (1433–99) was greatly intrigued by the questions on free will raised by the myth of Er in Plato’s Republic. By focusing on his Argumentum in Platonis Respublicam, this article discusses Ficino’s interpretation of the myth in light of his view on the faculties of the soul—intellect, reason, the imagination, and the vegetative power—and of how they become subject to providence or fate. Moreover, it will situate Ficino’s discussion of the myth within his understanding of the universe as an interconnected organism in which different levels of life are perfectly attuned with one another.