Janáček's original models for operatic writing were the operas of his older compatriot, Bedrich Smetana. These were essentially 'number' operas, dramas strung together by discrete arias, ensembles and choruses. But with the writing of Jenůfa he began to question the dramatic viability of these models, and he turned to a more concise, economical style of writing. As John Tyrrell points out in his article on the composer for The New Grove Dictionary of Music and Musicians, despite training in Leipzig and Vienna in the rudiments of Western classical style Janáček's intimate connection to the folk idioms of Moravia made it virtually impossible for him to conform to the phrase lengths and harmonic structures of his German, French and Italian contemporaries. Janáček's phrases are short, bordering on blunt. The motives or 'cells' upon which he builds a musical piece are in constant flux, we rarely hear them in the same form as they are initially introduced to us. He will occasionally utilize thematic reminiscence, rather like Verdi's purposeful repetition of suggestive themes in La traviata or the theme from the 'Friendship' Duet in Don Carlo which is heard a number of times in the opera to produce an emotional effect. But typically, a motive or small group of motives will be used to unite one scene of the opera, and these motives will be varied constantly in order to both unite the elements of the scene and to keep the drama moving ahead.
A few of the more important motives used in the opera are introduced in the overture, which was written after most of the opera was completed. The first important motive is heard from the timpani, beginning in the fifth bar of the score. These eight notes simply outline the interval of a fourth, from F natural to B flat, and they are responsible for helping to create the ominous atmosphere of the first section of the overture. But notice that the very same pitches (F natural and B flat) are used to build the 'sleigh bell' motive that appears in the oboe about two minutes into the overture when the tempo picks up. Suddenly the emotional atmosphere has changed, shifted, even though the composer is using the very same melodic material for both moments.
Similar variation techniques are used in every scene of the opera, with the orchestra taking the lead in carrying the development, and the voices simply singing in a kind of parlando style above the instruments. Pay close attention to what occurs in the orchestra underneath the first words uttered by Kudryash in his first scene dialogue with Glasha, a gently rocking motive that is repeated again and again during their conversation. But notice how the nature of the rocking motive changes abruptly when Dikoj, the old merchant, is first seen by Kudryash in the distance and then enters, berating his nephew Boris. The 'rocking' motive of the previous conversation takes on a 'rollicking' nature as Dikoj tears into Boris for his seeming lack of ambition. These are not two different motives, but the same motive developed or varied. When Dikoj leaves and Boris and Kudryash begin their conversation another variant of the motive appears, until it seems to disappear with the entrance of the Kabanov family. This technique is used throughout the opera, with new motives being used for the appearances of new characters (Katya, Kabanicha) or for important dramatic moments (the love scene, the storm).
If it sounds complex, it is; at least for a musician. The great thing about it is that it is also used so intuitively by Janáček that you don't need to know that all of this variation technique is occurring in order to appreciate the work in the theatre. The composer's genius is such that the music fits so well with the drama, the communication of emotion is immediate and accessible.