Whereas in Arithmetic Questions are only resolved by proceeding from given Quantities to the Quantities sought, Algebra proceeds in a retrograde Order, from the Quantities sought as if they were given, to the Quantities given as if they were sought, to the End that we may some Way or other come to a Conclusion or equation, from which one may bring out the Quantity sought. And after this Way the most difficult problems are resolved, the Resolutions whereof would be sought in vain from only common Arithmetic. Yet Arithmetic in all its Operations is so subservient to Algebra, as that they seem both but to make one perfect Science of Computing; and therefore I will explain them both together.

Arithmetica Universalis (1707)