 Of the two main parts of Bolzano’s formal logic, the extensional logic of ideas (the logic of classes) and the extensional logic of propositions, the first part comes from a long tradition beginning with Boethius (and derived from Aristotelian syllogistic) and ending — in Bolzano’s times — with Gergonne. Bolzano did not take his logic of classes from Gergonne or Euler, the most influential authors in their time, but rather from a small booklet entitled Outline of Logic (Grundriß der Logik) by a now completely forgotten logician, J.G.E. Maaß, published in 1793.