 Gundisalvi adopts central principles for the division of the sciences from Avicenna: that the principal criterion of division between the sciences is their subject matter; that a science cannot demonstrate the existence of its own subject matter; and that there are two kinds of subordination of a science: either as a part (pars) of another science, when it studies a part of its subject matter, or as a species (species) of another science, when it studies the subject matter in a specific respect (Hugonnard-Roche 1984; Fidora &amp; Werner 2007, 24–35).