Treatments of Aristotle's moral-political science have largely disregarded the methodological statements that he delivers as he embarks on his "philosophy of human affairs" in book I of the Nicomachean Ethics. A consideration of these statements, however, lends critical support to the view that Aristotle sought to give the sharpest possible expression to ordinary moralpolitical opinion. Moreover, apart from revealing the by-no-means ordinary reasons that induced Aristotle to do so (and to do so in contrast to Plato), such a consideration sheds light on the source of the vagueness or ambiguity that defines moral-political opinion as such. Indeed, the methodological statements are perhaps the first entries in the old quarrel of "relevance versus rigor." And, through them, Aristotle suggests how political scientists today might walk a fine line between "politics," on one hand, and "science," on the other, without losing sight of the ultimate tension between them.