Some proponents of epistemological approaches to argumentation (Biro, Siegel, Lumer, Goldman) assume that it should be possible to develop non-relative criteria of argument evaluation. By contrast, this paper argues that any evaluation of an argument depends (a) on the cognitive situation of the evaluator, (b) on background knowledge that is available for this evaluator in a certain situation, and (c)—in some cases—on the belief-value-system this person shares.