Mere repetition, of course, is not, strictly speaking, development, however efficient it may be as a means of building up musical structures. With the repetition of the motif at a different place in the scale, however, such as is used in the “answer,” we have a true development, though an elementary one. Here all the metrical and harmonic relations of the motif are kept intact, at the same time that the bodily shifting of it in the scale throws upon it, so to speak, a new light. This will be felt at once by any musical person who will play over attentively the two subjects and answers of Figure VIII. A much more radical change is effected when the motif is changed from major to minor, or vice versa, or presented in some key other than the dominant and more remote, or presented with new harmonization. Still, even in such cases, the metrical and fundamental harmonic form of the subject remains unaltered.
In the device called “inversion,” much used by Bach, we have an essential change. The metrical form of the subject, remaining unchanged, ensures recognizability, but the harmonic relations, while remaining identical in respect of size, are exactly reversed in respect of direction; in other words, the subject is turned upside down. A few examples will explain this better than many words.
[Music: score] [Illustration: FIGURE IX. EXAMPLES OF INVERSION.]
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.