Comparing composers is a traditional game of music historiography: from Palestrina and Lasso to Schonberg and Stravinskij. The case of Haydn and Mozart however is special. They are the only pair of composers who worked at the same time and in the same cultural context. They knew each other well and shared a mutual personal and professional respect. Together they are considered to be the creators of what is commonly seen as the definitive formulation of Viennese classical music. At the same time, their individual representations of the classical style are so different that these can be seen as complementary, extreme positions. So this unique historical constellation provides us with a chance to reach a deeper understanding of this style by means of comparison. The article deals with the two composers' extremely different musical socialization leading to very different results, their social character their careers, and finally their personal style, seeing Mozart's as a transformation of the logical system underlying Haydn's instrumental language into a theatrically informed musical idiom, which is visible in the prototypes of his own mature style demonstrated in the string quartet K 387, and again, in a different way, in the C Minor Mass K 427.
