At Jena the professor of mathematics was Erhard Weigel but Weigel was also a philosopher and through him Leibniz began to understand the importance of the method of mathematical proof for subjects such as logic and philosophy.
At Jena ang propesor ng matematika ay Erhard Weigel ngunit Weigel ay din ng isang pilosopo at sa pamamagitan ng kanya Leibniz nagsimula na maunawaan ang kahalagahan ng mga paraan ng matematika patunay para sa mga paksa tulad ng lohika at pilosopiya.