Translation of "Ipse dixit" into English

Commonly said in Medieval debates referring to Aristotle. Used in general to emphasize that some assertion comes from some authority, i.e., as an argument from authority, and the term ipse-dixitism has come to mean any unsupported rhetorical assertion that lacks a logical argument. Originally coined by Cicero in his De Natura Deorum|I, 10| to describe the behavior of the students of Pythagoras.