Definitions II
Definition 1.
 Given a rational straight line and a binomial, divided into its terms, such that the square on the greater term is greater than the square on the lesser by the square on a straight line commensurable in length with the greater, then, if the greater term is commensurable in length with the rational straight line set out, let the whole be called a first binomial straight line;

 But if the lesser term is commensurable in length with the rational straight line set out, let the whole be called a second binomial;

 And if neither of the terms is commensurable in length with the rational straight line set out, let the whole be called a third binomial.

 Again, if the square on the greater term is greater than the square on the lesser by the square on a straight line incommensurable in length with the greater, then, if the greater term is commensurable in length with the rational straight line set out, let the whole be called a fourth binomial;

 If the lesser, a fifth binomial;

 And, if neither, a sixth binomial.