Theories of tonal music take for granted that all keys of the same mode (i.e., all major and all minor keys) are employed by composers in essentially the same way; however, newer analytical and cognitive research challenges this view by pointing to aspects of transpositional nonequivalence among the keys. The present study offers possibly the first systematic, data-driven investigation of correlations between the choice of absolute key and structure across a composer's body of works. By performing an extensive corpus-based analysis of music by Wolfgang Amadé Mozart (1756–91), we derive 55 prototypes, subsuming phenomena from three independent domains: dynamic-rhetoric gestures that launch orchestral works, digressions to the parallel minor in sonata-allegro movements, and the occurrences of a particular six-note motive across Mozart's complete oeuvre. Ten prototypes display a significant association with a specific key after correction for multiple comparisons, amounting to a statistically significant total. Investigation of key-related musical structure offers fresh insight into Mozart's compositional decisions and the relation between schemata and their instantiations in his works, at the same time suggesting a revised perspective on traditional key characteristics. Mozart's perfect pitch offers one possible explanation for the role of key-related structure in his works; however, we also contemplate other possible explanations
