Recent rhetorical critiques of philosophy and science assume a contrast between rational argument and rhetoric that is inherited from an antirhetorical tradition in philosophy. This article rejects that assumption. Rhetoric is compatible with reasoned discourse in a strong sense originally outlined by Aristotle. Rhetorical analysis reveals the inadequacy of purely demonstrative accounts of rational argument and cognitive accounts of the conditions for rational assent to propositions. Social studies of the rhetoric of science, and in particular of credibility claims, need not fall into the forms of relativism and global antirealism with which they have become associated.