Aristotle's On Interpretation (Latin: De Interpretatione, Greek: Περὶ Ἑρμηνείας, Peri Hermeneias) is the second text of the Organon, the collection of short logical works that formed the basis of a traditional philosophical education in much of antiquity and the middle ages.
It begins with an analysis of the basic elements of language, before noting that is only when the parts of speech are brought together to form sentences, that we have propositions that can be said to be true or false. The bulk of the treatise considers the nature of propositions in more detail.
The works most famous passage features the famous sea-battle argument, an early statement of the problem of future contingents.
Free online texts
Biblioteca Online de Ciências da Comunicação: On Interpretation, translated by E.M. Edgehill, PDF file.
Internet Archive: L 325 - The Categories and On Interpretation, translated by Harold P. Cook. Prior Analytics, translated by Hugh Tredennick. Greek and English Loeb edition. Multiple formats.
Internet Classics Archive: On Interpretation, translated by E.M. Edgehill. HTML and TXT files.
University of Adelaide (Internet Archive): On Interpretation, translated by E.M. Edgehill. HTML text.
Wikisource: On Interpretation, translated by O.F. Owen. HTML text.
Historyoflogic.com: Semantics and Philosophy of Language in Aristotle's De Interpretatione.
History of Philosophy without any gaps: Aristotle's Logical Works - podcast by philosopher Peter Adamson.
Internet Archive: The Sea-Battle Hub - defunct website on Aristotle's sea-battle argument.
Internet Encyclopedia of Philosophy: Aristotle: Logic.
Librivox: On Interpretation - public domain audiobook.
Philosophiques: Le Chapitre IX du De Interpretatione D'Aristotle, by Jules Vuillemin.
Stanford Encyclopedia of Philosophy: Aristotle's Logic, by Robin Smith.
Wikipedia: De Interpretatione.
The Great Conversation: Further reading at Tom's Learning Notes
Porphyry: Isagoge - formed part of the medieval Ars Vetus or old logic, along with the Categories and On Interpretation.
Ancient Greek resources: Learn to read Greek classics in the original.