inherent in C D, then it is evident that B is also inherent in C, and in D, according to something else common, and that also according to something else, so that between two terms, infinite terms may be inserted, but this is impossible. It is not then necessary that the same thing should always be inherent in many, according to something common, since indeed there will be immediate propositions; it is moreover requisite that the terms should be in the same genus, and from the same individuals, since that which is common will be of those which are essentially inherent, for it is impossible to transfer things which are demonstrated from one genus to another.
But it is also manifest that when A is with B, if there is a certain middle, we may show that B is with A, and the elements of this are these and whatever are media, for immediate propositions, either all of them, or those which are universal, are elements. Yet if there is not (a medium) there is no longer demonstration, but this is the way to principles. In like manner, if A is not with B, if there is either a middle, or something prior to which it is not present, there is a demonstration, but if not, there is no demonstration, but a principle, and there are as many elements as terms, for the propositions of these are the principles of demonstration. As also there are certain indemonstrable principles, that this is that, and that this is present with that, so there are also that this is not that, and that this is not
