A dialectical theorem of pure reason must accordingly have the fol lowing feature, distinguishing it from all sophisticale propositions: it does not concern an arbitrary question that one might raise only at one's option, but one that every human reason must necessarily come up against in the course of its progress; and second, this proposition and its opposite must carry with them not merely an artificial illusion that disappears as soon as someone has insight into it, but rather a natural and unavoidable illusion, which even if one is no longer fooled by it, a thesis with antithesis.