Greek κανών (kanōn), a measuring rod or rule
Epicurus' name for his theory of knowledge: the "measuring stick" against which every claim about the world is tested. He wrote a book called the Canon, now lost, and his followers called this part of the philosophy "canonics" in place of the logic and dialectic of the other schools.
The canon names three criteria (standards) of truth: the sensations, the anticipations (prolēpseis), and the feelings of pleasure and pain. See The Criteria of Truth.
1. Key Texts
Quote from Diogenes Laertius 10.31Thus Epicurus, in the Canon ('Yardstick'), says that sensations, preconceptions and feelings are the criteria of truth. The Epicureans add the 'focusings of thought into an impression.' (tr. Long & Sedley)