In this regard, Pliny's influence over the medieval period has been argued to be quite extensive. For example, one twentieth century historian has argued that Pliny's reliance on book-based knowledge, and not direct observation, shaped intellectual life to the degree that it "stymie the progress of western science". This sentiment can be observed in the early modern period when Niccolò Leoniceno's 1509 "De Erroribus Plinii" ("On Pliny's Errors") attacked Pliny for lacking a proper scientific method, unlike Theophrastus or Dioscorides, and for lacking knowledge of philosophy or medicine.