 Christian August Crusius was born 10 June 1715 in Leuna, near Halle, the son of a pastor (and his mother was a pastor’s daughter). He matriculated at the University of Leipzig in 1734, where he studied a number of subjects but was particularly interested in theology and philosophy. At Leipzig, Crusius came under the influence of the philosopher (and physician) Adolf Friedrich Hoffmann (1707–1741), a disciple of Andreas Rüdiger (1673–1731) who had been a close associate of Thomasius. Crusius attained the Magister in philosophy in 1737 and habilitated in philosophy in 1740. He followed his philosophical studies with a baccalaureat in theology in 1742, though he would proceed to seek a position in the philosophy faculty. To this end, he defended two dissertations in philosophy, one of which, the Dissertatio philosophica de usu et limitibus principii rationis determinantis, vulgo sufficientis (Philosophical Dissertation on the Use and Limits of the Principle of Determining Reason, commonly called Sufficient) of 1743 was a critical discussion of the principle of sufficient reason. He became a professor of philosophy (extraordinarius) at Leipzig in 1744.