In his Second Paralogism of the Critique of Pure Reason, Kant described what he called the "Achilles of all dialectical inferences in the pure doctrine of the soul". This argument, which he took to be powerful yet fatally flawed, purports to establish the simplicity of the human mind, or soul, on the basis of the unity of consciousness. It is the aim of this volume to treat the major figures who have advanced the Achilles argument, or who have held views bearing on it.