This paper uses argumentation tools to show by means of analyzing nine cases from law and politics how argument strategies using persuasive definitions and quasi-definitions are powerful rhetorical tools of persuasion. By bringing to lightthe argumentation structure found in these examples, it is shown that definitions and redefinitions can have serious legal and political implications. Persuasive definitions and quasi-definitions are modeled as two distinct strategies for altering the relationship between classification and evaluation of a state of affairs. Persuasive definitions are aimed at modifying the relationship between the definiendum and its referent. In quasi-definitions some characteristics of an entity or event leading to a specific value judgment are selected and made accessible, while other conflicting ones are excluded. Reframing an issue is shown to be related to both strategies.