Sibelius found a source of inspiration in the modality embedded in folk music. His encounter with the singing of Pedri Shemeikka caused a veritable burst of compositions based either on folk melodies, or more often on melodies of his own making composed in the spirit of the music of Karealian singers and kantele players; the melodic style of Finnish-Karelian folk music can be found everywhere in his music. In addition to influencing melodic organization, modality pervades Sibelius's way of harmonizing his melodies. Sibelius invented some peculiar harmonization procedures, sometimes mode-specific. The paper illustrates several of these procedures in the Five Sketches for piano, op. 114, which belong to the pieces where the composer developed a musical language in which the traditional major-minor tonality is intermingled with the modes and new strategies of modal organization.