use of folk song. Other works, such as Tchaikovsky's last three symphonies, employ a personal musical idiom that facilitated intense emotional expression. Compositional style Melody American music critic and journalist Harold C. Schonberg wrote of Tchaikovsky's "sweet, inexhaustible, supersensuous fund of melody", a feature that has ensured his music's continued success with audiences. Tchaikovsky's complete range of melodic styles was as wide as that of his compositions. Sometimes he used Western-style melodies, sometimes original melodies written in the style of Russian folk song; sometimes he used actual folk songs. According to The New Grove, Tchaikovsky's melodic gift could also become his worst enemy in two ways. The first challenge arose from his ethnic heritage. Unlike Western themes, the melodies that Russian composers wrote tended to be self-contained: they functioned with a mindset of stasis and repetition rather than one of progress and ongoing development. On a technical level, it made modulating to a new key to introduce a contrasting second theme exceedingly difficult, as this was literally a foreign concept that did not exist in Russian music. The second way melody worked against Tchaikovsky was a challenge that he shared with the majority of Romantic-age composers. They did not write in the regular, symmetrical melodic shapes that worked well with sonata form, such as those favored by Classical composers such as Haydn, Mozart or Beethoven; rather, the themes favored by Romantics were complete and independent in themselves. This completeness hindered their use as structural elements in combination with one another. This challenge was why the Romantics "were never natural symphonists". All a composer like Tchaikovsky could do with them was to essentially repeat them, even when he modified them to generate tension, maintain interest and satisfy listeners. Harmony Harmony could be a potential trap for Tchaikovsky, according to Brown, since Russian creativity tended to focus on inertia and self-enclosed tableaux, while Western harmony worked against this to propel the music onward and, on a larger scale, shape it. Modulation, the shifting from one key to another, was a driving principle in both harmony and sonata form, the primary Western large-scale musical structure since the middle of the 18th century. Modulation maintained harmonic interest over an extended time-scale, provided a clear contrast between musical themes and showed how those themes were related to each other. One point in Tchaikovsky's favor was "a flair for harmony" that "astonished" Rudolph Kündinger, Tchaikovsky's music