After writing and defending his dissertation "On the Concept of Irony with Continual Reference to Socrates" (1841), Kierkegaard left Copenhagen in October 1841 to spend the winter in Berlin. The main purpose of this visit was to attend the lectures by the German philosopher Friedrich Wilhelm Joseph Schelling, who was an eminent figure at the time. The lectures turned out to be a disappointment for many in Schelling's audience, including Mikhail Bakunin and Friedrich Engels, and Kierkegaard described it as "unbearable nonsense". During his stay, Kierkegaard worked on the manuscript for "Either/Or", took daily lessons to perfect his German and attended operas and plays, particularly by Wolfgang Amadeus Mozart and Johann Wolfgang von Goethe. He returned to Copenhagen in March 1842 with a draft of the manuscript, which was completed near the end of 1842 and published in February 1843.