This episode argues that the forgotten foundation of Stoic practice is its rigorous system of logic, which was considered the essential tool for achieving a virtuous life. Stoic education was a unified system comprised of three interconnected parts: logic, physics, and ethics, often compared to a fertile field where logic is the protective wall. For the Stoics, virtue is the perfection of reason, and therefore, training in logic was not an abstract academic exercise but the primary method for improving one's moral character. The ultimate goal was eumonia, a flourishing state of being, which they believed was solely dependent on virtue. The Stoic theory of knowledge hinges on the concept of the kataleptic phantasia, or cognitive impression, which is a clear and accurate perception of reality that compels assent. This became their criterion of truth, developed in direct response to the intense skepticism of rival philosophical schools. A crucial aspect of their logic was distinguishing between what is within our control—our judgments and volitions—and what is not, ensuring our reason is applied correctly. Chrysippus, a key figure, developed a sophisticated system of propositional logic, analyzing the structure of arguments to ensure consistency and coherence in one's beliefs. Ultimately, the Stoics saw pathological emotions like intense anger or fear as resulting from logical errors—specifically, assenting to false propositions about what is good or evil. By sharpening the "sword of reason" through logical training, a practitioner could dissect their impressions, reject false judgments, and prevent these destructive emotions from taking hold. This makes logic not just a part of their philosophy, but the very engine that powers the journey towards virtue, tranquility, and a flourishing life.