The Enlightenment ideal of “pleasing variety” was a secondary issue when it came to Classical melody. Rather the demand was for plainness, for relief from the complex, richly ornamented lines of the Baroque period. When people at the time demanded “natural” melodies, what they meant were tunes: uncomplicated, singable melodies with clear phrases (and not too many of them), melodies with easily grasped parallelisms and balances.

In their move toward melodic simplicity, composers of the Classical period moved much closer to popular music, even folk music, than their Baroque predecessors had done. There is a definite popular lilt in Haydn’s music that people have traced to the Croatian folk melodies he heard as a child. Short tunes — or, more often, attractive little phrases that sound as though they might easily grow into tunes — are heard again and again in Classical symphonies and quartets. Tunes are not the only melodic material to be heard in these works, as we will see in a moment. Nevertheless, by comparison with a Baroque concerto, a Classical symphony leaves listeners with a good deal more to hum or whistle as they leave the concert.

Indeed, entire tunes were often worked into larger compositions. For example, variation form (theme and variations) grew popular both for separate pieces improvised by virtuosos and for movements in multimovement genres. Haydn wrote variations on a tune of his devising that would later become the German national anthem, and Mozart wrote variations on “Twinkle, Twinkle, Little Star,” in its original French version, “Ah vous dirai-je, maman” (Oh mama, I must tell you). Occasionally, popular songs were even introduced into symphonies. There is a contemporary opera tune in Mozart’s “Jupiter” Symphony, the last he composed, and one of his greatest.