The Short

378 TEMPO MODIFICATION
(b) There can be a gradual slowing down or speeding up of the pulse over several beats or bars.
(c) It can involve the adoption of a slower or faster basic tempo for a whole phrase or section, either abruptly
or preceded by a ritardando or an accelerando. In such cases the change of speed can either be slight, and
scarcely perceptible to the casual listener, or can result in the establishment of an unmistakably different
tempo.
2. The classic tempo rubato occurs when the accompaniment (or in the case of a keyboard instrument usually the
left hand) remains steady, while the melodic line is modified for a more or less extended passage.
(a) A single note or occasionally a rest may be lengthened where it has a particular expressive or structural
function, and the time that is lost will be regained by hurrying the immediately following beats.
(b) Sometimes the relationship of the melodic line to the bass will be modified throughout a phrase, an
extended passage, or even a whole movement. This technique was widely used, particularly in the eighteenth
century, to create a special effect or to vary a passage on repetition. It required particular skill and
understanding of the rules of composition on the part of the performer not to produce intolerable
harmonic clashes with the bass, though it is clear that the retardation and anticipation of essential harmony
notes, even when the technique was employed by experts, will sometimes have caused effects that would not
normally have been written down.
(c) In addition to or instead of redistribution of the note values, embellishments in the form of fiorituras might
be added to the melodic line in such a way that it appears to be rhythmically independent of the
accompaniment. The employment of this technique can be traced from C. P. E. Bach and Franz Benda to
Dussek, Chopin, and beyond, though with the passage of time, as with many of the above-mentioned tempo
rubato devices, the technique became a resource for the composer rather than for the performer.
Modication of the Basic Pulse
Many eighteenth-century musicians besides C. P. E. Bach discussed the types of tempo modification that involved a
real disturbance of the basic pulse, and a few more pedagogically minded or meticulous ones attempted to indicate it
graphically. Georg Friedrich Wolf used signs for various kinds of ritardando in his keyboard method of 1783, 729 and
Türk introduced several symbols for tempo modification into his Sechs leichte Klaviersonaten published the same year.
729 Unterricht, 85 ff.