  A rich source of semiotic material is also to be found in the theologico-philosophical tradition. The loci classici of semiotic discussions in the Commentaries on the Book of Sentences (Liber Sententiarum) of Peter Lombard, the basic scholastic textbook in theology, are particularly the comments on book 1, distinction 1: the sign as subject and means of all instruction; bk. 1, dist. 3: the differences between images and traces and their respective epistemic value; bk. 1, dist. 27: mental concepts, spoken words and their signification; bk. 2, dist. 10: the communication of  angels;[2]  and, last but not least, bk. 4, dist. 1: the sacramental sign and the sign in  general.[3]  Outside the philosophical and theological discourse, the notion of sign traditionally played an important role in the theory and practice of medical diagnostics (Maierù 1981: 64ff).