In various parts of Ethics, Spinoza explains both the existence and the necessity of the existence of things, like God, through their perfection(Proofs and Scholium to theorem 11 of part 1 and Scholium 2 for Theorem 33 of part 1). In this paper I attempt to elaborate on the suggestion made by Don Garrett, in Spinoza's Necessitariansim (2018), that Spinoza might have thought that no other world is possible but the one that expresses the greatest possible perfection. I will show that Spinoza's understanding of perfection is intimately connected with "Spinoza's PSR" and his understanding of casuality, to make Garrett's suggestion more probable. The paper is motivated by Koistinen's concerns, in Spinoza's Proof of Necessitarianism (2003), that Garrett's suggestion is too weak to entail necessitarianism. I'll show that Koistinens presented concerns can be rebutted and that the explication for the perfection of the world or "system of finite modes" that he ascribes to Garrett is flawed because it doesn't reflect how Spinoza uses the notion of perfection in Ethics. / <p>Höstterminen 2023</p>