The purpose of this paper is to inquire into the relationship between persuasive definition and common knowledge (propositions generally accepted and not subject to dispute in a English Saddle discussion).We interpret the gap between common knowledge and persuasive definition (PD) in terms of potential disagreements: PDs are conceived as implicit arguments to win a potential conflict.Persuasive definitions are analyzed as arguments instantiating two argumentation Gift Shaped Acrylic Plaque schemes, argument from classification and argument from values, and presupposing a potential disagreement.The argumentative structure of PDs reveals different levels of disagreement, and different pos-sibilities of resolving the conflict or causing dialogical deadlock.