Posterior Analytics (Bouchier)/Book I/Chapter XXVIII

Chapter XXVIII: What constitutes one or many Sciences

 * A science is one when it applies to a single genus, and when all the principles used belong to that science. Otherwise demonstration would be impossible (cf. Bk. I, c. 7).

Those sciences are one and the same which belong to the same genus, namely those which have the same primary principles and common parts or essential qualities. One science differs from another when their elementary principles are not drawn from the same source, and when the principles of one science are not derived from those of the other. A proof of this may be seen when one reaches the indemonstrable propositions of a science. These, if the sciences be one, must belong to the same genus as the things which are demonstrated. Another proof of this is that the things demonstrated are homogeneous to those indemonstrable propositions by which they are proved.