Aristotle · Philosophy
Aristotle’s invention of formal logic - the syllogism and the systematic study of valid reasoning - which governed Western thought for over two thousand years.
Aristotle did something no one had done before: he founded the systematic study of logic - the science of valid reasoning, of how conclusions can be validly drawn from premises. Before Aristotle, people reasoned and argued, but no one had systematically studied the forms of valid reasoning - what makes an inference valid, how conclusions follow from premises, what distinguishes good reasoning from bad. Aristotle invented this study, analysing the structure of arguments and identifying the forms of valid inference. His logical works (collected as the Organon, the ‘instrument’ of reasoning) founded formal logic as a systematic discipline - one of the most original and influential intellectual achievements in history, and the foundation of rigorous reasoning in philosophy, science, and mathematics for over two thousand years.
Aristotle’s deepest logical insight was that the validity of an argument depends on its form or structure, not its content. The argument ‘All A are B; all B are C; therefore all A are C’ is valid by virtue of its form - whatever A, B, and C stand for. Whether we substitute ‘men, mortals, mammals’ or ‘triangles, three-sided figures, polygons,’ the argument is valid because of its structure, regardless of its specific content. Aristotle thus discovered that validity is a matter of logical form - that arguments can be valid or invalid by virtue of their structure, independent of their particular content - and he studied the forms of valid inference abstractly, using letters (variables) to represent the terms and analysing the patterns of valid reasoning. This insight - that validity is a matter of form, that reasoning can be studied formally and abstractly - was a profound and revolutionary discovery, founding the formal study of logic and revealing the abstract structure of valid reasoning.
Aristotle’s logic was so complete and powerful that it reigned, almost unchallenged, as the logic - the definitive account of valid reasoning - for over two thousand years, one of the longest reigns of any theory in intellectual history. From antiquity through the Middle Ages and into the modern era, Aristotle’s logic (the syllogism, the laws of thought, the analysis of valid inference) was studied, taught, and used as the foundation of rigorous reasoning in philosophy, science, theology, and education. The great philosopher Kant could still write, two thousand years later, that logic had not had to advance a single step since Aristotle, and seemed to be complete. For over two millennia, Aristotle’s logic was the unchallenged foundation of the study of valid reasoning - a testament to the completeness and power of his original achievement. Only in the nineteenth and twentieth centuries would a new, more powerful mathematical logic (Frege, Russell, and others) finally surpass and absorb Aristotle’s logic - extending and deepening, but building on, the formal study of reasoning that Aristotle had founded.
This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.
You learned that Aristotle founded formal logic with the syllogism and the systematic study of valid inference. Explain what logic is and what Aristotle achieved, in your own words.
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