The paper calls for argumentation theory to learn from moral and political philosophy. Several thinkers in these fields help understand the occurrence of what we may call legitimate dissensus: enduring disagreement even between reasonable people arguing reasonably. It inevitably occurs over practical issues, e.g., issues of action rather than truth, because there will normally be legitimate arguments on both sides, and these will be incommensurable, i.e., they cannot be objectively weighed against each other. Accordingly, ‘inference,’ ‘validity,’ and ‘sufficiency’ are inapplicable (...) notions. Further distinctive features of pro and con arguments in practical argumentation are explored, and some corollaries are drawn regarding evaluative norms of legitimate dissensus. Examples from immigrationrelated public debates in Denmark are given. (shrink)