Acceptance of a paradigm in the scientific community depends upon persuasion, upon the supplying of "good reasons" for supporting one paradigm over another. When one paradigm gains long-term acceptance and becomes the standard for scientific thought, scientists defer to such an authority in their thinking, and such established paradigms serve to guide the practice of science. Consequently, when in the course of a scientific revolution a new paradigm is offered as a challenge to old standards of thinking, the burden of proof is on the challenger, who must now prove good reasons for the shift based on principles of argumentation. Before scientific revolutions occur, an established paradigm has presumption over all challenging theoretical frameworks until sufficient proof is adduced against it. Scientists help to entrench such frameworks by specialized vocabulary and skills which narrow their vision and increase their resistance to change. Paradigms that challenge existing thought, unless they can be accommodated by the old framework, will meet resistance from researchers whose work is grounded in the established paradigm and students who traditionally defer to authority. Once a paradigm has successfully challenged an older framework, it will continue to be regarded as a counter-presumption until it, too, becomes the norm and no longer must defend itself. (References are included.) (JC)