By revisiting the Phädon's proof of the indestructibility of the soul, this paper casts light on the sources that lie in the background of Mendelssohn's dialogue. After discussing Wolff's use of the Law of Continuity against the possibility of natural annihilation as a precedent for Mendelssohn's argument, I show that the latter is also heavily indebted to Boscovich's argument against the possibility of contiguity in the continuum. I contend that Mendelssohn's appropriation of Boscovich's argument is influenced by Wolff's treatment of the hypothesis of the soul's transformation. I conclude with some remarks on Kant's refutation of the Phädon's proof in light of his possible acquaintance with Boscovich's natural philosophy.