The twentieth century brought great development in the field of rhythm, in the following two ways:

• 1. The structure and development of rhythm in general became richer and more diversified;

• 2. Interest in percussion increased, while other instrumental groups were also assigned important rhythmic functions.

In Stravinsky's The Soldier's Tale melodic and percussive instruments are on an equal footing. Works featuring extensive percussion parts include Stravinsky's The Wedding, Bartók's Sonata for two pianos and percussion, Edgard Varèse's Ionisation, fragments from Milhaud's Les Choéphores, and Carl Orff 's Antigone. External influences may also be noted: not only the rhythms of Eastern music, but also those of indigenous folk music (Bartók) and jazz (Milhaud's La Création du Monde, Stravinsky's Ebony Concerto and Ragtime, Krenek's Johnny spielt auf, and Ravel's Sonata for violin and piano) made their mark on contemporary composition. A preference for irregular rhythmic structures emerged, whether spontaneously invented or rationally developed. In the latter case in particular, it is generally true to say that rhythm gained independence. Important structural principles, applied in the past particularly to melody and harmony, were now transplanted to rhythm (rhythmic canons, for example). On the other hand, melodic-harmonic structures were sometimes determined by rhythmic factors. An old and familiar example of this is The Rite of Spring, in which ‘percussive chords’ serve to highlight rhythmic figures, to which end they are complexly constructed:

This brings us to a matter of importance. Not without reason, indeed, did Stravinsky choose strong and complex chords. If we try to render the same rhythm with major triads, the effect proves much weaker; by placing the triads in a higher register, the result already improves. It appears, therefore, that rhythm is determined by other musical elements than duration and dynamics alone. Another example: if we play a melody in a tempo dictated exactly by the metronome, but first very high with short and strong staccato notes, and then low, soft and legato, the first version will seem slower than the second. Again, the duration of the notes is influenced by several elements: not only the notated, metronomic length, but the musical length too, that which is organically incorporated into the whole and to which we react. In a piece of music, innumerable subtle forces react to one another.