Epicurus applies his method of inference (the use of observations as signs, Asmis' summary, p. 333: "the method of using the phenomena as signs (σημεῖα) of what is unobserved") immediately to the atomic theory of Democritus. In Aristotle's "Prior Analytics", Aristotle himself employs the use of signs. But Epicurus presented his 'canonic' as rival to Aristotle's logic. See: Lucretius (c. 99 BCE – c. 55 BCE) "De rerum natura" ("On the nature of things") a didactic poem explaining Epicurus' philosophy and physics.