If we investigate what is distinctive about differential calculus by the simple inventory of what there is in this part of mathematics, we find the following as the subject matter: (a) Equations in which any number of magnitudes (here we need simply confine ourselves to two) are combined into one determinate whole in such a way that, first, the equations themselves derive their determinateness from empirical magnitudes which are their fixed limits, and also from the kind of link which they have with these limits and with each other as is generally the case in an equation; but since there is only one equation for Cf.