In 1994 he received the PhD in Art history at the University of Cologne. His dissertation was published in 1998 as The works of mercy in art from the 12th to the 18th centuries. Iconographic changes caused by the early modern reception of rhetorics. The study explores art theory and rhetorics as driving forces for the persuasive mode in early modern art.Cf. the abstract of the German publishing house Georg Olms.
