ians ▁Ger tr ude ▁Ber th old , ▁Lor enz ▁D itt mann , ▁, ▁, ▁ ▁and ▁Max ▁Im d ahl ▁and ▁he ▁is ▁frequently ▁quoted ▁by ▁English ▁and ▁American ▁art ▁histor ians . ▁For ▁instance , ▁Geoff rey ▁Gr ig son ▁said , ▁" P ain ting ▁is ▁a ▁difficult ▁subject ▁to ▁write ▁about , ▁and ▁searching ▁books ▁on ▁particular ▁pain ters ▁are ▁as ▁rare ▁as ▁un ic orn s ... ▁One ▁of ▁them , ▁and ▁how ▁welcome , ▁is ▁Dr ▁Kurt ▁B adt ' s ▁The ▁Art ▁of ▁C é z anne . ▁According ▁to ▁Robert ▁Hob bs , ▁" B adt ' s ▁study ▁is ▁particularly ▁helpful ▁in ▁art icul ating ▁certain ▁aspects ▁of ▁[ Mal col m ] ▁Mor ley ' s ▁overall ▁program ▁that ▁has ▁definite ▁aff in ities ▁with ▁C é z anne ' s ." ▁Mary ▁Jacob us ▁calls ▁B adt ▁a ▁" p ione ering ▁writer ▁on ▁Const able ' s ▁clouds ". ▁The ▁Times ▁Liter ary ▁Supp lement ▁called ▁Const able ' s ▁Cloud s ▁the ▁best ▁book ▁on ▁Const able ▁since ▁Les lie ' s ▁Life . ▁Rudolf ▁Arn heim ▁often ▁c ites ▁B adt ▁in ▁his ▁widely ▁read ▁Art ▁and ▁Visual ▁Per ception . ▁He ▁writes : ▁" It ▁may ▁seem ▁par ado x ical ▁for ▁Kurt ▁B adt ▁to ▁say ▁that ▁Rub ens ▁is ▁one ▁of ▁the ▁simplest ▁of ▁all ▁artists . ▁He ▁explains , ▁' It ▁is ▁true ▁that ▁in ▁order ▁to ▁grasp ▁his ▁simplicity , ▁one ▁must ▁be