De InterpretationeAristotle

De Interpretatione is Aristotle's treatise on the proposition, the unit of language that can be true or false. Where the Categories classifies terms and the Prior Analytics studies the syllogism, this work occupies the middle ground: how words combine into statements, and what determines their truth-value.

Aristotle distinguishes names and verbs, then shows how they compose into affirmations and denials. Every declarative sentence asserts or denies something of a subject, and every such sentence is either true or false. He maps the logical relations among propositions (contradiction, contrariety, subcontrariety) and introduces the square of opposition that would organize logic for two millennia.

The most famous chapter is the ninth, on future contingents. If it is true now that there will be a sea-battle tomorrow, does that make the sea-battle necessary? Aristotle resists this conclusion. He argues that propositions about singular future events do not yet have determinate truth-values, preserving the reality of contingency against logical fatalism. The chapter has generated commentary from the Stoics through Boethius to modern modal logic, and its central question, whether the future is fixed by present truths, remains one of the deepest problems in the philosophy of language and time.