Husserl himself taught philosophy as a Privatdozent at Halle from 1887 , then as professor , first at Göttingen from 1901 , then at Freiburg from 1916 until he retired in 1928 .
Then Husserl taught philosophy , as a Privatdozent at Halle from 1887 , and as a professor : He initially studied mathematics but then started attending lectures on psychology and philosophy .