Many other examples might be given, for Bach is endlessly ingenious in his use of inversion, and all the composers who followed him have used it. Its effect, as will be seen from the examples, is most stimulating; the mind easily perceives the likeness to the original subject, since the rhythm is retained intact; yet the turning upside down of all the pitch relations produces most unexpected and interesting features.
So much for modifications dependent on altered tonal relationships. Those produced by metrical alterations are if anything even more serviceable to the composer. The simplest metrical change possible is produced by increasing or decreasing the actual duration of all the tones in the motif, while retaining jealously their proportionate duration. Thus the identity of the motif is not tampered with, but it is made to bear a new relation to its musical context. This device is named augmentation or diminution, according as the time-values of the motif are augmented or diminished.
In Fugue VIII, Book I, W.-T.C.,
becomes by augmentation,
In Fugue II, Book II, W.-T.C.,