As a professor of philosophy and liberal arts, Engel taught both Alexander and Wilhelm von Humboldt. He served with the Berlin Academy of Sciences and was a co-director of the National Theatre at Berlin. Engel's foremost contribution to musical literature was as an aesthetician. He compared the objectivity of tone-poems with the subjectivity found in general expression. According to Engel music lends itself better to the latter concerning the conveyance of ideas outside of music. Tone-poems were only justified in the case of music with words. "Musical objectivity" could only partially be achieved for music can never depict the objects that one has feelings about. ~ Keith Johnson, All Music Guide