  The unknown author, now commonly named Ps.-Robert Kilwardby, opens his commentary on Priscianus maior (written somewhere between 1250 and 1280)[18]  by modifying Augustine's prominent dictum that “all instruction is either about things or about signs” into the stronger and more ‘semiotic-minded’ thesis that “every science is about signs or things signified” (scientia omnis aut est de signis aut de rebus significatis) (Ps.-Robert Kilwardby: Comment. on “Prisc. Maior”, 1975, 1). This statement he takes as starting point of a detailed discussion of the questions of whether there can be a (special) science of  signs[19]  and, if so, what its relationship towards the sciences dealing with things would be  like.[20]  Ps.-Kilwardby points out that there are several ‘sciences of signs’ (diversae sunt scientiae de signis) according to the various kinds of signs (Ps.-Robert Kilwardby: Comment. on “Prisc. Maior”, 1975, 3). Since, however, any discipline, in order to meet the Aristotelian standard of science as it began to be accepted at that time, must have a general subject matter, the scientia de signis necessarily contemplates the sign “in terms of a universal notion abstracted from the particular signs” (sub ratione universalis abstracti a particularibus signis) (Ps.-Robert Kilwardby: Comment. on “Prisc. Maior”, 1975, 4). In case of natural signs (signa naturalia) as well as “moral signs” (signa moralia), as e.g., actions in relation to the good or bad will, the theory of signs cannot be separated from the theory of things signified; therefore, these signs fall under natural and moral science, respectively (Ps.-Robert Kilwardby: Comment. on “Prisc. Maior”, 1975, 6). The linguistic signs, however, produced by the human understanding for the purpose of communicating its ideas, are the subject-matter of a rational science (scientia rationalis), the science of signs.