An Etymological Dictionary of the German Language/Annotated/dürfen

by Friedrich Kluge

dürfen, anom. verb, ‘to be allowed, venture, need,’ from Middle High German dürfen, durfen, a preterite present, ‘to have reason, cause, be permitted, need, require’; Old High German durfan, preterite present, ‘to lack, be destitute of, require, be in need of’; compare Gothic þaúrban, Dutch durven, Anglo-Saxon þurfan, ‘to be in need of.’ In addition to the Teutonic root þurf, þurb, Swiss points to an old parallel form þurp. In the Modern High German derivative darben, Bedürfnis, Notdurft, bieder, &c., the primary sense of the root þrf, from tṛp, ‘to be destitute of, lack,’ still appears.