In 1879 Gottlob Frege published “Begriffsschrift,” roughly “Concept Script, a formula language of pure thought modeled on that of arithmetic,” a short book that broke with the term logic descended from Aristotle. Its central innovation was the system of quantifiers, the notation for “for all” and “there exists” together with bound variables, which let logic express general statements about relations in a way older logic could not. This is the predicate logic that every later logician, and every computer scientist, would go on to use.