Chrysippus Quote on Logic: The First Science

Quote

"Logic is the science of argument and the foundation of the philosophical life: the person who cannot reason cannot live well, for every act of the wise person is an act of reasoning." — Chrysippus, as reported in Diogenes Laertius, Lives of the Eminent Philosophers, Book VII

Author

Chrysippus (c. 280–207 BCE) was the third head of the Stoic school and its greatest systematizer — the philosopher of whom it was said, "if Chrysippus had not existed, the Stoa would not have existed." His logic of propositions was the most advanced logic of antiquity.

Source

The quotation is a report of Chrysippus's doctrine preserved in Diogenes Laertius's Lives of the Eminent Philosophers, Book VII, in the doxographical account of the Stoic logic. It is a summary of the school's doctrine rather than a verbatim quotation.

Context

The Stoics divided philosophy into three parts — logic, physics, ethics — and they compared the system to an animal: logic the bones, physics the flesh, ethics the soul. Chrysippus made the logic the most technically developed part of the system: his logic of propositions analyzed the conditional, the disjunction, and the conjunction, and his five "indemonstrables" — the basic valid argument forms from which all others were derived — were the most advanced logical theory of antiquity. The claim that logic is the foundation of the philosophical life reflects the Stoic conviction that reason is the essence of the human being: the person who cannot reason correctly cannot judge correctly, and the person who cannot judge correctly cannot live well.

Meaning

The quotation states the Stoic account of logic with complete clarity. "Logic is the science of argument" — the definition: the discipline that analyzes the forms of correct reasoning. "The foundation of the philosophical life" — the role: the logic is not a technical specialty but the foundation of the whole, because every judgment, every choice, every act of the philosophical life is an act of reasoning. "The person who cannot reason cannot live well" — the consequence: the errors of reasoning are the errors of life — the false judgments that produce the passions, the false evaluations that produce the disturbances. "Every act of the wise person is an act of reasoning" — the ideal: the sage is the person whose reason is completely reliable, and the logic is the discipline of that reliability. The quotation is the foundation of the Stoic epistemology, and it connects the Stoic tradition to the wider history of logic — the discipline that Chrysippus raised to a level not reached again until the nineteenth century.

Related Wisdom

The quotation belongs to the Stoic account of reason and the foundation of the Stoic wisdom tradition. Its account of logic as the foundation of the philosophical life connects to the Stoic epistemology of the cognitive impression and to the wider history of logic — the propositional logic of Chrysippus anticipates the logic of the modern era, and its insights are the inheritance of the analytic tradition.