The Rule of Three, or Golden Rule of Arithmeticall whole Numbers. Be the three termes given 2 3 4. ...To finde their fourth proporcionall Terme: that… - Simon Stevin

We call the wise age that in which men had a wonderful knowledge of science which we recognize without fail by certain signs, although without knowing who they were, or in what place, or when. ...It has become a matter of common usage to call the barbarous age that time which extends from about 900 or a thousand years up to about 150 years past, since men were for 700 or 800 years in the condition of imbeciles without the practice of letters or sciences—which condition had its origin in the burning of books through troubles, wars, and destructions; afterwards affairs could, with a great deal of labor, be restored, or almost restored, to their former state; but although the afore-mentioned preceding times could call themselves a wise age in respect to the barbarous age just mentioned, nevertheless we have not consented to this definition of such a wise age, since both taken together are nothing but a true barbarous age in comparison to that unknown time at which we state that it [i.e., the wise age] was, without any doubt, in existence.

The seventh Definition. The Golden Rule, or Rule of three, is that by which to three tearmes given, the fourth proportionall tearme is found.

The second Definition. Number is that which expresseth the quantitie of each thing.