The stoics divided philosophy into three branches: logic, physics, and ethics. Logic covered not only the rules of correct argumentation, but also grammar, linguistics, rhetorical theory, epistemology, and all the tools that might be needed to discover the truth of any matter. Physics was concerned with the nature of the world and the laws that govern it, and so included ontology and theology as well as what we would recognize as physics, astronomy, and cosmology. Ethics was concerned with how to achieve happiness, or how to live a fulfilled and flourishing life as a human being. A stoic sage was supposed to be fully expert in all three aspects.
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