The central thematic structure of Vocalise is a vocal part without text. The singer’s task is demanding, as the melodic material must almost always be performed using the glissando technique, keeping the pitch in constant motion while simultaneously maintaining control over intonational anchor points. The accompanying instruments also avoid clearly defined pitch material—partly through glissandi (as a link with the vocal part), and partly through an impressionistic haze created by tremolos.
The acoustic character of the piece suits concert venues with longer reverberation times (such as churches or chapels), as its tempo is not fast and allows for emphasis and development of overtone resonances. From the perspective of glissando-based melodic writing, it evokes a reminiscence of chant. Thus, although the piece is saturated with motion, it may still appear static—and vice versa.