 (i) The notion of a per se attribute is ultimately linked with the idea that in a scientific theory the admissible terms must be salient properties of the objects under investigation. Avicenna argues that it is only through this regimented conceptual vocabulary that the two defining conditions of scientific knowledge (necessity and explanatory character) can be met by a theory. In doing so, he provides a systematic account of per se which elaborates on Aristotle’s cursory remarks in Posterior Analytics A4 and A22. The Aristotelian analysis of per se is based on the relation of “being part of the definition, i.e. of the essence, of something”: a term A is per se 1 with respect to another term B if and only if A is part of the definition of B while a term A is per se 2 with respect to another term B if and only if B is part of the definition of A.